Introduction to Molecular Genetics
Session 4: Molecular Genetics
1. Explain the Chemical Structure of RNA
Ribonucleic acid (RNA) is composed of three different molecules:
A pentose D-ribose.
One of the following nitrogenous bases:
Purine: adenine (A) and guanine (G).
Pyrimidine: cytosine (C) and uracil (U).
A molecule of phosphoric acid.
The binding of ribose by a carbon-nitrogen base 1 of the pentose is called a nucleoside, and a nucleoside binding to a molecule of phosphoric acid through the 5′ carbon of deoxyribose is called a nucleotide.
The union of several ribonucleotides for binding 5′-3′ phosphodiester gives rise to ribonucleic acid (RNA), which is therefore also called a polynucleotide. The sequence of nucleotides to form a nucleic acid is always made by phosphoric acid, which binds the 3′ carbon of the pentose of the next nucleotide. This molecule has two ends: one 3′ end and one 5′ end.
2. Cite the Chemical and Structural Differences Between RNA and DNA
According to chemical composition, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) differ in:
DNA: It contains the pentose deoxyribose, and the nitrogenous bases are A, G, C, and T.
RNA: The pentose is ribose, and the nitrogenous bases are A, C, G, and U.
Regarding the structure of nucleic acids, DNA and RNA have the following differences:
DNA: Presents different levels of organization, known as primary structure, secondary, tertiary, and quaternary.
The primary structure consists of the sequence of nucleotides in the chain.
The secondary structure was proposed by Watson and Crick in 1953. Their studies revealed that the DNA molecule is a right-handed double helix.
The tertiary structure refers to the packaging of the DNA molecule with histone proteins to form the chromatin of eukaryotic cells.
The quaternary structure occurs in eukaryotic cell division; DNA is packaged further to form the chromosomes.
RNA: There are three types that are found as single polynucleotide chains with the same composition, but each type has many different molecular structures:
The messenger RNA (mRNA) has only a primary structure.
It copies the genetic information contained in DNA (transcription) and transports it to the cytoplasm, where protein synthesis takes place in ribosomes.
It is synthesized in the nucleus and transmits the information to the cytoplasm.
The transfer RNA (tRNA) has a specific primary and secondary structure called cloverleaf.
It transports amino acids to the ribosomes, placing them on the mRNA to form a polypeptide chain according to the genetic message encoded in RNA.
The different types of tRNA are synthesized in the nucleus and perform their function in the cytoplasm.
Ribosomal RNA (rRNA) has a tertiary structure that is produced by binding different molecules of rRNA to ribosomal proteins, leading to the subunits that make up the ribosome.
It constitutes, together with ribosomal proteins, ribosomes and is therefore involved in protein synthesis.
Different types of rRNA are synthesized in the nucleus and perform their function in the cytoplasm.
3. Discuss the Structure of Transfer RNA and Explain its Function
Transfer RNA (tRNA) has a primary and secondary structure. The primary structure consists of the sequence of ribonucleotides in the chain. The secondary structure is shaped like a cloverleaf because of the existence in the molecule of double-stranded regions formed by pairing by hydrogen bonds between complementary bases. The different types of tRNA are synthesized in the nucleus and perform their function in the cytoplasm.
The tRNA is responsible for transporting amino acids to the ribosomes, placing them on the mRNA to form a polypeptide chain according to the genetic message of the latter. This process is based on each of the different types of tRNA, which has in one of its links a region called the anticodon, composed of three specific nucleotides that are complementary to some triplet of mRNA called the codon.
Session 4: Molecular Genetics
1. Comment, Aided by These Schemes, on the Levels of Chromatin Organization and Highlight the Differences Between Interphase Chromatin and Metaphase Chromosomes
The images represent different structural levels that deoxyribonucleic acid (DNA) adopts in eukaryotic cells. From left to right, we see:
Image A represents the double helix of DNA.
Image B corresponds to the decondensed chromatin fiber. It refers to the provision that DNA adopts to be associated with histone proteins. In 1974, Kornberg said that structurally, chromatin is formed by sequential units consisting of a central or core histone globule around which DNA coils. Each “bead” of the necklace, with a spherical, discoid, or slightly cylindrical shape (Dudet et al.), was given the name nucleosome and has a diameter of 10 nm.
Image C represents the interphase chromatin fiber. This is the fundamental substance of the nucleus of eukaryotic cells at the interface. Observation of chromatin in the electron microscope reveals a 30-nm fibril formation. Histone H1 is not part of the nucleosome but binds to DNA segments that relate to form this structure. It is now accepted that the chromatin fiber has a folded structure in the form of a solenoid with varying degrees of coiling. The first degree of coiling matches the 30-nm fiber.
Image D corresponds to the second degree of coiling of chromatin with a diameter of 300 nm.
Images E and F represent the “superespiralización” that plagues the chromatin at the time of initiating mitosis, where it condenses to form chromosomes with a diameter of 1,400 nm.
The nucleus in mitotic division is characterized by the individualization of the hereditary material, and the chromatin condenses into chromosomes.
Chromosomes are cylindrical structures that are identical in number and morphology in all cells of individuals of a species. They reach maximum condensation in metaphase and anaphase, when they are best displayed.
At the molecular level, the two chromatids that make up the chromosome represent two identical DNA molecules since they come from DNA replication in the interphase period.
Block 3: The Heart: The Structure of Information
2. Define the Following Terms: Chromatid, Chromosome, and Centromere
A chromatid is each element into which the centromere divides the chromosome longitudinally. Each chromatid has only one DNA molecule, which is the morphological manifestation that the genetic material is duplicated. At the molecular level, the two chromatids that make up the chromosome represent two identical DNA molecules since they come from the duplication of DNA in the interphase period.
Chromosomes are cylindrical structures that are identical in number and morphology in all cells of individuals of a species. They reach maximum condensation in metaphase and anaphase, when they are better displayed.
The centromere is a constriction that divides the chromosome into two arms of the same or different size. It contains constitutive heterochromatin, i.e., compacted and genetically inactive chromatin in all cells. The centromere contains the so-called kinetochore of a protein nature, which is the portion of the chromosome that hooks into the spindle microtubules involved in the separation of sister chromatids during anaphase of meiosis and mitosis. The centromere’s function is to hold the two sister chromatids together.
Chromatin is the fundamental substance of the nucleus of eukaryotic cells at the interface. The nucleus in mitotic division is characterized by the individualization of the hereditary material, and the chromatin condenses into chromosomes.
Block 1: Chemical Ingredients of the Cell
1. The General Structure of an Amino Acid. Concept of Peptide
Amino acids are the constituents or monomers that form proteins. Amino acids are organic compounds composed of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N), which are characterized by having in their molecule a carboxyl group (-COOH), an amino group (-NH2), and a side chain or R group, all covalently bonded to a carbon atom called the α carbon.
A peptide is formed by the linking of amino acids by a peptide bond, which is a covalent bond that occurs between the carboxyl group of one amino acid and the amino group of another, with the formation of a water molecule. The union of two amino acids forms a dipeptide; therefore, in a similar way, three amino acids can be joined by two peptide bonds to form a tripeptide, four to form a tetrapeptide, etc. When we have joined several amino acids, we have oligopeptides, and when many are joined, a polypeptide.
2. Cite the Types of Bonds that Stabilize the Tertiary Structure of a Protein
The tertiary structure of a protein refers to the arrangement of the secondary structure in space and therefore the type of three-dimensional conformation that it possesses. The biological functions of proteins depend on the tertiary structure that they possess.
The tertiary structure of a protein is stabilized through bonds that occur between the R-groups of its constituent amino acids. These bonds are:
Hydrogen bonds.
Electrostatic attraction between oppositely charged groups.
Hydrophobic attractions and van der Waals forces between aliphatic or aromatic side chains.
Disulfide bonds between cysteine residues.
3. Explain the Biological Functions of Proteins
From a functional standpoint, proteins are the most versatile organic biomolecules that exist, i.e., they can perform varied functions. The main biological functions they play in the organization are:
Reserve function of certain compounds.
Transport function of various substances.
Defense function.
Contractile function.
Enzyme function.
Homeostatic function.
Hormonal function.
Structural function.
2. What is ATP? Explain the Structure and Indicate Some Processes in Which This Molecule Is Essential
Adenosine triphosphate (ATP) is a nucleotide, and the structural units that form it are:
A purine nitrogenous base: adenine.
A pentose: ribose.
Three molecules of phosphoric acid.
Metabolic reactions are coupled with energy through ATP. In cellular metabolism, reactions occur that release energy and others that consume it (energy is released in catabolism and consumed in anabolism). These energetic processes need not occur simultaneously or in the same place in the cell. Therefore, a mechanism must exist to store and transport that energy from places where it is released to where it is consumed. This mechanism is based on the formation and subsequent breaking of chemical bonds that store and release large amounts of energy, which are called high-energy bonds. ATP is a molecule of great biological importance, not only as a coenzyme but also because of the biochemical energy that it can store in two ester-phosphoric bonds.
Block I: Chemical Ingredients of the Cell
1. Explain the Structural Levels of Proteins
The composition and shape of a protein are defined by four structures. They have a hierarchical nature, i.e., they involve levels or degrees of increasing complexity leading to the four types of structures:
Primary structure: The linear sequence of amino acids it contains, i.e., the number and the order in which they occur. Peptide bonds between amino acids keep this structure stable.
Secondary structure: Refers to the regular periodic arrangement in space of the polypeptide chain along one direction. One can also say that it is the arrangement of the primary structure in space and that it is a direct result of the self-turning ability of the α carbon. There are two models or types of secondary structures:
α-helix.
β-sheet.
Tertiary structure: Refers to the arrangement of the secondary structure in space and therefore the type of three-dimensional conformation that it possesses. The most frequent conformations that proteins adopt are globular and filamentous. The biological functions of proteins depend on the tertiary structure that they possess.
Quaternary structure: Refers to proteins that are composed of more than one polypeptide chain and refers to the way in which the chains or subunits associate to form the active protein (e.g., hemoglobin). The different subunits are joined by hydrogen bonds and disulfide bonds.
2. What Is the Denaturation of Proteins? Types and Causes of Distortion Causes
The way to determine the importance of the specific structure of a protein for its biological function is to alter this and determine the effect of the alteration on the function. An extreme disturbance is the total cancellation of the three-dimensional structure. This process is called denaturation. Denaturation of proteins can be carried out by heat, extremes of pH, and the action of organic solvents and detergents.
Denaturation of proteins is always associated with the loss of biological activity. However, some proteins can recover their structure and therefore their biological activity in a process called renaturation if they are returned to conditions in which their native conformation is stable.
2. Explain the Composition and Functions of Lysosomes
Lysosomes are membrane-bound organelles containing hydrolytic enzymes inside capable of degrading all kinds of biological polymers.
3. Discuss the Functional Differences Between Smooth Endoplasmic Reticulum and Rough Endoplasmic Reticulum
The general function of the endoplasmic reticulum is related to the synthesis and transport of molecular components, including biological membranes, proteins, and lipids. However, at the functional level, we also distinguish between rough and smooth endoplasmic reticulum:
Rough: Protein synthesis occurs in ribosomes that are attached to the membrane. These synthesized proteins are discharged within the endoplasmic reticulum and are stored or transported to other organelles or cell sites. Some proteins are part of the membrane of the reticulum and may well become part of other cell membranes (the plasma membrane or other organelles). Protein glycosylation begins inside the reticulum, to be completed in the Golgi apparatus.
Smooth: It is related to lipid synthesis, storage, and transport, particularly phospholipids and cholesterol. It detoxifies substances harmful to the cell from outside or inside the cell.
6. James Watson and Francis Crick Received the Nobel Prize in Physiology or Medicine in 1962 for Discovering the Structure of DNA
a. Without Going into the Chemical Formulas of its Components, Describe the Basic Structural Characteristics of the DNA Molecule
a. The Watson and Crick model proposed the following basic structural features of the DNA molecule:
DNA consists of two right-handed polynucleotide chains, coiled in a helix around a single axis, thus forming a double helix. Both chains or strands are antiparallel, i.e., the 3′-5′ internucleotide phosphodiester bridges go in opposite directions, one going in one direction and the other in the opposite direction.
The purine and pyrimidine bases of each of the chains or strands are stacked inside the double helix, with their planes parallel and perpendicular to the axis of the double helix. The bases of one chain are paired by hydrogen bonds with the bases of the other strand. Allowable pairs are A-T and G-C.
The two antiparallel strands of the double helix are not identical in sequence or composition. Instead, they are complementary to each other (if one strand has an A, the other has a T, and vice versa).
The bases are stacked at a distance of 0.34 nm from center to center, which is the distance between each pair of bases. In each complete turn of the double helix, there are exactly 10 nucleotides, corresponding to the repeat distance of 3.4 nm in height. The double helix is about 2.0 nm in diameter.
The bases are located in the relatively hydrophobic interior of the helix, and the sugar residues and the polar, negatively charged phosphate groups are exposed to water on the periphery, forming the external skeleton of the double helix.
The double helix is stabilized not only by hydrogen bonds between complementary base pairs but also by electronic interactions between the stacked bases, as well as by reciprocal hydrophobic actions.
b. Semiconservative DNA replication was proposed by Watson and Crick and demonstrated experimentally by Meselson and Stahl in 1957. DNA replication takes place during the synthesis or S phase of the cell cycle of the interface and is semiconservative because the DNA molecule splits into its two strands, each of which directs the synthesis of its complement, forming two identical molecules with an old strand and a new strand each.
1. Describe the Chemical Composition of a Nucleotide [0.5] and Represent Their Structure [0.5]. Explain Two of its Functions [1]
A nucleotide consists of a nitrogenous base linked to a pentose, which in turn is attached to a molecule of phosphoric acid.
The pyrimidine bases result from the pyrimidine ring of cytosine (C), thymine (T), and uracil (U). The purine bases are derived from the purine ring. Thymine is only found in DNA, and uracil is only found in RNA.
The pentoses can be β-D-ribofuranose (ribose), which is found in RNA nucleotides or oligonucleotides, and β-D-2-deoxyribofuranose (deoxyribose), which is present in DNA nucleotides or deoxyribonucleotides.
The union of the nitrogenous base and the pentose results in a nucleoside. This union takes place through an N-glycosidic bond between the nitrogenous base and C1′ of the pentose.
Nucleotides are phosphate esters of nucleosides. The ester bond occurs between the hydroxyl group on carbon 5′ of the pentose and phosphoric acid.
The structure of a nucleotide (with adenine as the nitrogenous base) is:
(Insert image of nucleotide structure here)
Nucleotides are the monomers that make up nucleic acids, DNA, and the different types of RNA (mRNA, rRNA, tRNA, snRNA). Other non-nucleic acid nucleotides are ATP (adenosine triphosphate) and ADP (adenosine diphosphate), which are energy carriers. ATP acts as the “energy currency of the cell.” cAMP (cyclic adenosine monophosphate) transmits and amplifies within cells signals arriving via the blood and hormones, which are the “first messengers.” When cAMP is referred to, it is called the “second messenger.” Coenzyme nucleotides act as carriers of electrons; FMN and FAD are coenzymes of dehydrogenases, like NAD and NADH, that are involved in different processes such as cellular respiration.
Coenzyme A, CoA-SH for short, is the carrier of acyl groups (R-CO-). A derivative, acetyl-CoA, is important in cell metabolism.
1. Describe the Tertiary and Quaternary Structures of Proteins, Indicating the Links and Stabilizing Forces That Characterize Them [2]
The composition and shape of a protein are defined by four structures. These have a hierarchical nature, i.e., they involve levels or degrees of increasing complexity leading to the four types of structures: primary, secondary, tertiary, and quaternary.
The tertiary structure of a protein refers to the arrangement of the secondary structure in space and therefore the type of three-dimensional conformation that it possesses. The most common conformation adopted by proteins is globular. The biological functions of proteins depend on the tertiary structure that they possess.
The tertiary structure occurs when the secondary structures (α-helix and β-sheet) undergo superfolding or supercoiling, resulting in very complicated geometric figures in space, specific to each protein. Many globular proteins have a tertiary structure, resulting from a ball-shaped fold. The tertiary structure is maintained by several types of weak bonds (hydrogen bonds, van der Waals forces, hydrophobic and ionic interactions, and electrostatic interactions), but one of the most important is the covalent disulfide bond (-S-S-) established between the sulfur atoms of amino acids such as cysteine when they are facing each other.
The quaternary structure of a protein refers to proteins that are composed of more than one polypeptide chain and refers to the way in which the chains or subunits associate to form the active protein (e.g., hemoglobin). The different subunits are joined by hydrogen bonds and disulfide bonds.
1. Define the Primary Structure of a Protein [0.5], Indicating the Bond That Characterizes It [0.25] and the Chemical Groups Involved in This Bond [0.25]. What Is Meant by Denaturation of a Protein? [0.5] What Organelles Are Involved in the Synthesis and Packaging of Proteins? [0.5]
The composition and shape of a protein are defined by four structures. These have a hierarchical nature, i.e., they involve levels or degrees of increasing complexity leading to the four types of structures: primary, secondary, tertiary, and quaternary.
The primary structure of a protein is the linear sequence of amino acids it contains, i.e., the number and the order in which they occur.
Amino acids are linked together covalently by peptide bonds that develop between the carboxyl group of one amino acid and the amino group of the next, with the formation of a water molecule. Therefore, polypeptide chains have a free amino group and a free carboxyl group at the ends of the molecule, called the N-terminus and the C-terminus, respectively.
The denaturation of a protein is an extreme disturbance in its three-dimensional structure and is always linked to the loss of biological activity. In the process of denaturation and renaturation of proteins, relevant conclusions can be drawn about them. First, the sequence of the protein determines its three-dimensional structure, and second, the three-dimensional structure determines the biological function of proteins. Denaturation of proteins can be carried out by heat, extremes of pH, and the action of organic solvents and detergents.
Ribosomes are cellular organelles present in all cells, in the cytoplasm, and inside chloroplasts and mitochondria. They consist of rRNA and protein. The function of the ribosome is the same in all cells and is involved in protein synthesis.
The main function of the rough endoplasmic reticulum is protein synthesis and storage. Protein synthesis is performed on ribosomes that are attached to the membrane. These synthesized proteins are discharged within the endoplasmic reticulum and are stored or transported to other organelles or cell sites. Some proteins are part of the membrane of the endoplasmic reticulum and may well become part of other cell membranes (the plasma membrane or other organelles).
A. About Biomolecules:
1. Which of the Molecules in the Drawing Are Part of a Nucleic Acid? What About a Protein?
2. What Types of Nitrogenous Bases Are Known? Cite Two Bases That Appear in DNA
3. What Role Does DNA Play in the Body? What Is its Structure?
4. What Is the Role of Messenger RNA in the Body? What About Transfer RNA?
5. Could the Molecule in the Drawing Be Part of DNA? Explain Your Answer
1. The molecules in the drawing that are part of a nucleic acid are the nitrogenous base adenine (B) and the adenine nucleotide (D).
The molecule in the drawing that is the monomer of proteins is the amino acid (C).
2. The two types of nitrogenous bases that form nucleic acids are purine bases and pyrimidine bases.
DNA contains the following four types of nitrogenous bases:
Purine: adenine (A) and guanine (G)
Pyrimidine: cytosine (C) and thymine (T)
3. The role of DNA in organisms is related to the storage and transmission of hereditary information, constituting the molecular basis of heredity. It also directs and regulates cell function.
DNA has different levels of organization, known as primary structure, secondary structure, tertiary structure, and quaternary structure.
The primary structure consists of the sequence of nucleotides in the chain.
The secondary structure of DNA was proposed by Watson and Crick in 1953. Their studies revealed that the DNA molecule is a right-handed double helix.
The tertiary structure refers to the packaging of the DNA molecule with histone proteins to form the chromatin of eukaryotic cells.
The quaternary structure occurs in eukaryotic cell division; DNA is packaged further to form the chromosomes.
The structure of DNA proposed by Watson and Crick showed that DNA is a double helix consisting of two polynucleotide chains coiled around an imaginary axis. The nitrogenous bases are complementary within the two chains and are held together by hydrogen bonds. The planes of their rings are parallel and perpendicular to the double helix. Thus, it resembles a spiral staircase where the steps are the nitrogenous bases and the railings are the chains formed by the pentose and phosphate.
4. The role of mRNA is to copy the genetic information contained in DNA (transcription) and transport it to the cytoplasm, where protein synthesis takes place in ribosomes.
tRNA is responsible for transporting amino acids to the ribosomes, placing them on the mRNA to form a polypeptide chain according to the genetic message encoded in the mRNA.
5. DNA is a polymer because it consists of monomers called nucleotides, which contain the pentose deoxyribose in their composition. The molecule in the drawing is a disaccharide formed by the union of two hexoses and therefore can never be part of DNA.
3. Explain the Composition and Structure of the Cytoskeleton
Filamentous proteinaceous structures that form the cytoskeleton are found in the cytosol of a eukaryotic cell. It is a dynamic structure whose function is constantly reorganized.
The filamentous structures or components that constitute the cytoskeleton are interconnected, and their functions are coordinated. They are of three types:
Microtubules: These are the main components of the cytoskeleton of eukaryotic cells. They are 250 Å in diameter and consist of globular proteins called tubulins, which are arranged spirally so that there are 13 units per turn, leaving a central recess. They appear free in the cytoplasm, although most are arranged radially to the centrosome, which is a region near the cell nucleus, considered the microtubule-organizing center.
Microfilaments: These are protein filaments thinner than microtubules and are related to cell architecture and movement. The most characteristic protein is actin, whose units are joined together to form helical polymers in the form of strands. Actin molecules are also associated with other protein components, depending on the cell type involved. For example, in skeletal muscle, it is associated with myosin, troponin, and tropomyosin to build thick and thin filaments.
Intermediate filaments: These are so called because their size is intermediate between that of microtubules and microfilaments. They are filamentous protein structures of different chemical natures. They are not the same in all cells, and they may not even appear in some of them. They can be:
Tonofilaments: Formed by keratin.
Myofilaments: Formed by actin and myosin molecules.
Neurofilaments: Found in nerve cells.
The cytoskeleton is involved in maintaining or changing cell shape, in cell internal organization, and in the movement of endocellular organelles.
4. Identify the Structural Similarities Between Mitochondria and Chloroplasts
The endosymbiotic theory developed by L. Margulis associates bacteria with mitochondria and chloroplasts. According to this theory, the origin of the eukaryotic cell came from a primitive urkaryotic cell (host cell), which at one point engulfed prokaryotic organisms, establishing an endosymbiotic relationship. These engulfed prokaryotic cells would be the origin of mitochondria (which come from aerobic bacteria) and chloroplasts (photosynthetic bacteria).
Mitochondria and chloroplasts are organelles that have structural similarities: They have a size very similar to that of bacteria, they have their own double-stranded circular deoxyribonucleic acid (DNA), and they have ribosomes. Their DNA genome is similar to that of bacteria, and their ribosomes have the same sedimentation coefficient (70S) as bacterial ribosomes. Also, both are organelles limited by a double membrane.
2. With Respect to Ribosomes:
a) Explain Their Structure. b) Explain Their Chemical Composition. c) Explain Their Function. d) Indicate Their Location in Prokaryotes and Eukaryotes
b) Ribosomes are composed of rRNA and protein. For example, in eukaryotes, the small subunit is composed of one rRNA molecule and 21 different proteins, and the large subunit consists of two rRNA molecules and 34 different proteins.
c) The function of the ribosome is the same in all cells and is protein synthesis. For the formation of proteins to take place, ribosomes must be formed by both subunits, although the start of translation only requires the small subunit to bind to the mRNA.
d) In eukaryotic cells, ribosomes are free in the cytoplasm, attached to the rough endoplasmic reticulum membrane, and within mitochondria and chloroplasts. In prokaryotes, they are free in the cytoplasm and are never attached to membranes.
2. Solution
In the following outline of a plant cell, the major organelles and structures that characterize it are represented:
(Insert image of plant cell here)
The most important functions that the various structures perform are:
1. Endoplasmic reticulum: It is mainly responsible for the synthesis of proteins and lipids.
2. Golgi apparatus: It is responsible for the storage and transport of substances in the cytoplasm.
3. Chloroplast: its function is to carry out photosynthesis.
4. Mitochondrion: perform aerobic cellular respiration, which produces energy in the form of ATP.
5. Vacuole: maintains cell volume and turgor pressure by accumulating substances.
6. Chromatin: the macromolecule carrier of hereditary or genetic information.
7. Nucleolus: Performs rRNA synthesis, which the protein is assembled with ribosomal subunits.
8. Pared celular: mechanical supports and protects the cell as an exoskeleton, but without thereby prevent their growth. It also helps maintain hydrostatic equilibrium between the cell and the environment that surrounds it, which is hypotonic, preventing cell burst water limiting entry to this.
In many important respects there is agreement between animal cells and plant cells. Both possess plasma membrane and extracellular matrix may occur, although different in nature. Both have a cytoplasm which hosts a microtubule cytoskeleton, and both possess a membrane system. Both types of cells have a nucleus in forming the genetic material and undergo mitotic and meiotic divisions. However, plant cell organelles have the following exclusive rights:
– Cell wall, composed mainly by cellulose fibers arranged in concentric layers around the cell.
Plastids: photosynthesis is a unique anabolic process of plant cells takes place in chloroplasts.
– Vacuoles: are vesicles whose primary function is to maintain cell volume and turgor pressure by accumulating substances inside.
only possible to differentiate between two types of cells: prokaryotic and eukaryotic, the main difference between the first types, cells without nuclear envelope. Despite the differences between the two types of cellular organization, have important similarities and therefore both types are believed to descend from the same primitive cell.
Prokaryotic cells are usually small and relatively simple from the viewpoint of cytology, considering that they are representative of the first cell types encountered in biological evolution.
Eukaryotic cells are much more complex than prokaryotic, both structurally and functionally. Are characterized by the genetic material is isolated from the rest of the cell by a nuclear membrane, forming the nucleus. Furthermore, eukaryotic cells, the presence of cytoplasmic organelles causes cellular compartmentalization of the territory by organizing the space in different metabolic functions carried out by the cell.
In it the following schedule, are represented the structural differences of the two types of cellular organization:
n is the following schedule, are represented the structural differences of the two types of cellular organization:
INVOLVED
CYTOPLASM
CORE
Prokaryote
– Capsule
– Cell wall
– Plasma membrane invagination that forms by the mesosomes.
– Ribosomes
– Cytoplasmic inclusions
– Flagella
– Fimbriae or pili
They have no real core, presenting a nucleoid that a circular double-stranded DNA molecule free in the cytoplasm
EUKARYOTIC CELL
– Glycocalyx in animals
– Cell wall in plants and fungi
– Plasma membrane
– Ribosomes
– Endoplasmic reticulum
– Golgi apparatus
– Vacuoles
– Lysosomes
– Peroxisomes
– Mitochondria
– Plaster
– Cytoskeleton
– Centrosome
– Cilia and flagella.
– Chromatin
– Nucleolus
In the following drawings, are represented a prokaryotic cell and eukaryotic cell plant.
BLOCK 3: THE HEART: THE STRUCTURE OF INFORMATION
1.
The cell cycle includes the period of time from the onset until a cell divides and consists of two distinctly different phases or states:
The state of mitosis and cell division or separation of the daughter cells.
The state of division or interface or not cell growth period. In this state the cell performs its normal functions and, if it is to cell division, duplication or replication of deoxyribonucleic acid (DNA).
The interface in turn comprises three stages: G 1, S and G 2 and lasts for approximately 90% of the cell cycle.
3.
Meiosis occurs in the biological cycles of sexual reproduction to avoid duplicating the chromosome that would result in fertilization and to enhance the variability by combining genetic information that occurs between two individuals to form a new individual who, in turn , will feature a mix of characteristics of parents. The so-called genetic recombination is the result of interbreeding between homologous chromosomes and is responsible, along with the mutation, variability of living organisms, a phenomenon essential for evolution.