Essential Principles of Cell Biology and Biochemistry
Biological Molecules: Lipids and Their Functions
Lipids are organic molecules that are insoluble in water, with an oily, waxy, or fatty consistency. Their functions are to store energy, to participate in muscle contraction, to act as insulators, and to make up part of the cell membranes. There are three kinds of lipids:
- Fatty acids and waxes: These are only made up of carbon, hydrogen, and oxygen.
- Phospholipids: These also contain phosphorus and nitrogen. They are made up of a polar head with a phosphate group and two nonpolar fatty acid tails.
- Steroids: These are characterized by being made up of fused carbon rings. They are also lipids that make up part of cells; cholesterol is the most abundant steroid in animal cells and is used in the production of bile salts, vitamin D, and steroid hormones such as testosterone and estrogen.
Fats, which are made up of two or three fatty acids and glycerol, are a rich source of energy; they are found in butter and vegetable oil.
Proteins and Their Diverse Roles
Proteins are organic compounds made up of chains of amino acids. They are the most diverse molecules in living things and form the structural part of the body, like keratin, which makes up nails, scales, hooves, hair, and feathers.
- Enzymes: These are proteins in charge of different chemical reactions.
- Hemoglobin: Its function is transportation, since it is in charge of carrying oxygen to all body cells.
Nucleic Acids and Other Macromolecules
Nucleic acids are organic molecules that carry the genetic message of the cells. They are made up of subunits called nucleotides, in which the sugar of one nucleotide is bonded to the phosphate group of another.
Mucopolysaccharides are a type of long-chain macromolecule that contains sugars and are found located in body articulations. The cuticle is a protection film that is located in the most external layer of plants and is the one that interacts with the environment.
Foundations of Cell Biology
The cell is the anatomical and functional unit of living things, since it is capable of surviving independently—either as a unicellular or a multicellular organism. It meets all of the characteristics of life: reproduction, growth, metabolism, respiration, irritability, etc. All living things, from microscopic bacteria to whales, are made up of cells.
Key Figures in Cell Discovery
- Robert Hooke: The first person who used the term “cell.”
- Anton Van Leeuwenhoek: Designed lenses of up to 200x magnification; he discovered “animalcules.”
- Robert Brown: Discovered the nucleus in plant cells.
- Matthias Schleiden: Published that all plants were made up of cells.
- Theodor Schwann: Published his cell theory for the animal kingdom.
- Rudolf Virchow: Contributed to the improvement of the cell theory with his contributions on the origin of cells.
The Cell Theory and Classification
The Cell Theory states that all living things are made up of one or more cells, where all metabolic processes take place. New cells arise from the division of preexisting cells; it also recognizes that the cell is the unit of transmission of genetic information.
Prokaryotic vs. Eukaryotic Cells
There are two types of cells, prokaryotes and eukaryotes:
- Prokaryotes: Unicellular organisms that lack organelles or other internal membrane-bound structures; they do not have a nucleus.
- Eukaryotes: Cells that contain a nucleus and organelles and are enclosed by a plasma membrane.
Comparing Animal and Plant Cells
Both types of cells have organelles such as mitochondria, endomembranous systems, a nucleus, cytoskeleton, lysosomes, peroxisomes, and plasma membranes; however, we can distinguish some specific structures in each type of cell.
- Plant cells: Stand out for having chloroplasts that allow them to carry out photosynthesis, as well as a cell wall made up of cellulose that provides protection and support. They have huge vacuoles to store water and other nutrients. They also have plastids that serve as storage for carbohydrates such as starch.
- Animal cells: The vacuoles of animal cells, when they do have them, are not very big. They have centrioles that participate in cell division, and they can have cilia, flagella, or pseudopods.
Cell Membrane Structure and Transport
All cells have a structure called the cell membrane, which is crucial for the life of the cell, since it establishes the limits between the internal medium, called cytoplasm, and the extracellular medium.
Proteins in the Cell Membrane
- Integral proteins: Found either totally or partially encompassed by the lipid bilayer; they can completely cross the membrane and transmit signals from the exterior to the interior of the cell, such as transmembrane proteins.
- Peripheral proteins: Found attached to the bilayer or to the integral proteins.
Endocytosis and Exocytosis
The cells must carry out the processes of endocytosis and exocytosis when they need to introduce substances that cannot cross the membrane with the help of protein transporters. In endocytosis, the cell absorbs substances, and in this process, the cell membrane is crucial. In the same way, if the cell needs to get rid of very large substances, it carries out exocytosis.
Organelles and Their Vital Functions
Membrane-Bound Organelles
- Nucleus: Protection and access control of DNA.
- Endoplasmic Reticulum (ER): Control and modification of new polypeptide chains; lipid synthesis and other jobs.
- Golgi Apparatus: Modification of new polypeptide chains, classification, and shipment of proteins and lipids.
- Vesicles: Transport, storage, or digestion of substances in the cell.
- Mitochondria: ATP synthesis from the decomposition of sugars.
- Chloroplast: Sugar synthesis in plants and some protists.
- Lysosome: Intracellular digestion.
- Peroxisome: Inactivates toxins.
- Vacuole: Storage.
Organelles Without a Membrane
- Ribosomes: Assemble polypeptide chains.
- Centrioles: Anchor the cytoskeleton.
Genetic Material and Mutations
DNA is considered the molecular basis of life, since it is found in all living things. In DNA, we find the codes for all the characteristics necessary to generate a new individual; also, it controls all cellular activities and self-replication.
RNA molecules are diverse, as there are different types: messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA). These are in charge of transcription and translation of the information stored in DNA to convert it into a protein. Genes determined the differences that were inherited by individuals of the same species. Genes provide the genetic information necessary to make proteins in two steps: transcription and translation.
In transcription, a karyotype is used. During mitosis, in one phase of cell division, it is possible to observe the chromosomes in the microscope and see how they are arranged.
Types of Chromosomal Mutations
Point mutations can be classified in the following way:
- Chromosomal mutations: Affect a fragment of the chromosome and sometimes the whole chromosome.
- Deletion mutations: Loss of a chromosome fragment; an example of this type of mutation is Cri du Chat syndrome.
- Duplication mutations: A segment of a chromosome is duplicated and can either stay on the same chromosome or be inserted into another one.
- Inversion mutations: When a chromosome segment changes its orientation within the chromosome.
- Translocation mutations: A change in position of a segment of the chromosome.