Introduction to Cell Biology
CELL THEORY
- All living organisms are made of one or more cells.
- Cellular life is simpler. In other words, the cell is the basic unit (structural and functional) of living beings.
- All cells arise from a pre-existing cell. There is no spontaneous generation.
- Each independent cell is capable of feeding itself, interacting, and reproducing, although in multicellular beings it must be coordinated with other cells.
Basic Cellular Functions
Nutrition
Food provides nutrients: building material and energy to work, and waste.
Reproduction
Creation of identical copies or creation of modified copies (stem cells).
Relationship
Response to external stimuli: motion, substance production, or internal changes.
Minimum Membership of a Cell
Membrane, cytoplasm, genetic material (RNA, DNA):
– In the nucleus: eukaryotic cells
– In the cytoplasm: prokaryotes
Chloroplast
Organelle unique to plants used for photosynthesis (and some protists).
Symbiosis
A relationship between two living organisms in which they help each other without being able to live apart.
Reproduction of Cells
There are two possibilities:
A. The reproduction of a normal cell
B. The reproduction of a germ cell (the one that has to form gametes)
Reproduction of a Normal Cell
a) The division of the nucleus (mitosis).
Phases:
– Interface: when the cell does not divide
– Prophase: chromatin is grouped into chromosomes, the nucleus disappears in prophase, the centrioles become visible at opposite sides, between the two centrioles are formed protein rods (chromatic spindle)
– Metaphase: the chromatic spindle is already formed, the chromosomes are joined by their centromeres to the chromatic spindle rods
– Anaphase: the centrioles collect the chromatic spindle rods and each rod carries a chromatid
– Telophase: the chromosomes return to the state of chromatin and it turns around to form the nucleus while the chromatic spindle disappears.
b) The division of the rest of the cell (cytokinesis).
It occurs in:
– Animal cells: bipartition, budding, sporulation
– Plant cells: bipartition
Meiosis
This is cell division of germ cells (which have two copies of each chromosome, i.e., they are diploid) to produce gametes (which have only one copy of each chromosome, i.e., they are haploid). Meiosis occurs so that the gametes have half the normal number of chromosomes, i.e., one copy of each chromosome (haploid). The other reason is to produce genetic recombination, resulting in that not all gametes of an individual are equal. Meiosis consists of: 1st mitosis (abnormal) and 2nd mitosis (normal).
Genetics
The science of biology that studies how hereditary characteristics are transmitted from one individual to another.
Gene
A piece of DNA in chromatin or in chromosomes, where the information for the synthesis of a particular protein that is going to control a particular trait is found.
Alleles
Any specific information that a gene could give. Alleles may be different (heterozygous) or the same (homozygous).
Genome
The set of genes typical of a species.
Genotype
A set of genes and alleles specific to an individual.
Phenotype
An individual’s own physical characteristics and depends on the environment and genotype.
Mode of Inheritance
Dominant-recessive, codominant. The hereditary characteristics of a living being depend on their proteins, proteins depend on the amino acids they are made of. Those 20 kinds of amino acids are encoded by DNA codons. Each codon or triplet is formed by a combination of 3 nucleotides. Each nucleotide can be of 4 types according to the nitrogenous base it has.
Endoplasmic Reticulum
It consists of a set of tubules and vesicles. It is responsible for manufacturing and transporting various substances. The part of the endoplasmic reticulum that has ribosomes is called the rough endoplasmic reticulum, and the part without ribosomes is called the smooth endoplasmic reticulum.
Golgi Apparatus
A membranous organelle formed by a group of flattened vesicles and sacs. It takes substances from the endoplasmic reticulum and introduces them into vesicles for secretion.
Vacuole
Membranous structures that accumulate various substances. They are larger and more abundant in plant cells than in animal cells.
Lysosomes
Tiny vesicles containing substances capable of digesting large molecules captured by the cells.
Mitochondria
Cylindrical or elongated organelles composed of a double membrane. They are considered the power plants of eukaryotic cells because their function is to obtain energy through cellular respiration. They are found in all eukaryotic cells.
Cilia or Flagella
Mobile organelles formed from cytoskeletal protein fibers, which are appendages at the ends of some cells.
Chromosome
A condensed form of genetic material that is most useful for transportation and delivery.
Nucleolus
Spherical structure involved in the realization of the genetic message.