Cell Structure and Function: A Comprehensive Study
The Cell
The cell is classified as the driving, morphological, physiological, and reproductive element of living beings. It is classified as eukaryotic. In prokaryotes, it exists in all living organisms with a defined nucleus, mitochondria, and Golgi apparatus.
Plasma Membrane
The plasma membrane is made up of lipids, phospholipids, and membrane proteins distributed in layers. Certain proteins are enzymes; others are receptors for hormones or other substances.
Fundamental Parts of the Cell
The fundamental parts of the cell are the membrane, cytoplasm, and nucleus.
What is the Cell Wall?
The cell wall is a thick layer of cellulose located in all plant cells.
Functions of the Cell
- Limits and protects the cell
- Allows communication with neighboring cells
- Regulates the exchange of substances
Diffusion, Dialysis, and Osmosis
Diffusion is the movement of molecules from a region of high concentration to another of low concentration. In dialysis, dissolved substances pass through water or a solvent in osmosis.
Membrane Permeability
Permeability refers to the ability of a membrane to allow molecules or substances to pass through. It is termed permeable or impermeable depending on whether it allows passage or not. Differential or selective permeability refers to the passage of some substances and not others.
Cytoplasm Formation
The cytoplasm consists of an array and figurative elements or morphoplasma.
Mitochondria and Their Function
Mitochondria are corpuscles or organelles present in all cells. They tend to be cylindrical, elongated, or rounded, with a size of 1.5 microns. Their function is the release of energy, acting as the electric center of the cell.
Endoplasmic Reticulum and its Function
The endoplasmic reticulum is a vesicular system with structures similar to the nucleus. Its functions include acting as a secretory system, transporting substrates and products of the cytoplasm, and synthesizing cholesterol and other non-protein substances.
Golgi Apparatus and its Function
The Golgi apparatus is a set of mobile lipoprotein elements located in the cytoplasm near the nucleus. It is present in all eukaryotic cells, with the exception of red blood cells. Its functions include the temporary storage of proteins and compounds synthesized in the endoplasmic reticulum. In plant cells, it forms cellulose for the cell wall.
Ribosomes and Their Function
Ribosomes are small, oval-shaped corpuscles constant in the matrix. They are formed by rRNA, synthesized in the nucleolus, and go to the cytoplasm. Their function is to synthesize proteins by decoding the genetic information delivered by mRNA.
Lysosomes
Lysosomes are small organelles responsible for autolysis. They are in the form of granules or membranous vesicles and become active when they break their membranes in the endoplasmic space.
Vacuoles
Vacuoles are intracellular spaces limited by a membrane. They are bubble-like cavities containing isotonic liquids, gases, or solids and cytoplasm.
Plastids
Plastids are characteristic cell organelles of plant cells. Their size varies, and they multiply independently of the nucleus. There are three groups: floroplasts (pigmentary), chromoplasts, and reserve or leucoplasts.
Presence of the Nucleus
The nucleus is present in eukaryotic cells.
Location of the Nucleus
In animal cells, the nucleus is located in the center. In plant cells, it is displaced towards the periphery by vacuoles.
Structure of the Nucleus
The nucleus is formed by a double lipid membrane with two layers. It interacts with the rest of the cell through nuclear pores. The outer layer of the double membrane is continuous with the membrane of the endoplasmic reticulum and the Golgi apparatus.
Function of the Nucleus
The nucleus controls protein synthesis in the cytoplasm by sending molecular messengers.
Organization of DNA Molecules within the Nucleus
DNA molecules are organized into chromosomes, which often appear in identical pairs.
Transcription of Genetic Information
Transcription occurs when the nucleus synthesizes long chains of heterogeneous nuclear RNA from the instructions contained in DNA.
Translation of Genetic Information
Translation is where genetic information (DNA) is in the cytoplasm. RNA binds to ribosomes and encodes the primary structure of a specific protein.
Chromosome Sets
- Diploid: Two sets of chromosomes (pairs) – 2n
- Haploid: Only one member of each pair, and no chromosome is n (egg and sperm)
Nucleoli
Nucleoli are special regions where RNA is synthesized. They are needed to form immature ribosomal subunits that migrate to the cytoplasm through nuclear pores, where they join together to form functional ribosomes.
What is a Gene?
A gene is a unit of inheritance. Molecularly, a gene is defined as a DNA segment encoding information for protein synthesis.
Formation of Nucleic Acids
Nucleic acids are composed of carbon, oxygen, phosphorus, hydrogen, and oxygen (CHOMP). Their bases are paired so that adenine only binds with thymine and guanine with cytosine.
Structure of the DNA Molecule
The DNA molecule is formed by two long chains or filaments of nucleotides wound around each other, forming a double helix, resembling a long spiral staircase.
Characteristics of Homologous Chromosomes
Homologous chromosomes have the same shape, size, and genetic constitution.
Origin of Each Homologous Chromosome
The origin of each homologous chromosome is from the parents in sexually reproducing organisms.
Difference Between Phenotype and Genotype
- Phenotype: Determines the final character (external appearance) produced by genes, identified by the genotype and the environment in which an individual develops.
- Genotype: Genetic constitution according to the genes a person possesses. The phenotype is caused by the specific expression of the genotype.
Number of Chromosomes in Somatic Cells
The number of chromosomes in somatic cells is 46.
Number of Chromosomes in Human Sex Cells
Human sex cells have 22 autosomes + 1 sex chromosome, totaling 23 chromosomes.
Number of Chromosomes in a Person with Down Syndrome
A person with Down syndrome has 47 chromosomes.
Mutation and its Characteristics
A mutation is a change in RNA replication when one base is replaced by another. Most mutations are harmful to organisms, are recessive, and are heritable.
What is a Carcinogen?
A carcinogen is an environmental or artificial substance that can cause cancer.
Elements that can Cause Genetic Damage or Cancer
- Physical: X-rays, ionizing radiation
- Chemical: Lead, arsenic