Definition: the Cell Is the Basic Unit of Life

Cells, DNA and cell division

•Definition: the cell is the basic unit of life. •Cells allow us to eat, breathe, grow, reproduce and eliminate waste.

•Cell components visible under the microscope: •Cell membrane •Cytoplasm •Nucleus

Cell Component (Organelle) Function

Mitochondria Produces an energy molecule (ATP) through cellular respiration

Golgi Apparatus (Body) Stores and transports material within and outside of the cell

Endoplasmic Reticulum Modifies proteins and lipids and transports material

Ribosome Builds proteins (chains of amino acids)

Lysosome Breaks down and recycles molecules

Nucleus Contains and protects DNA (genetic material)

Cytoplasm Gelatinous material that establishes an environment that is hospitable for cellular activity

Cytosol Intracellular fluid made of dissolved substances in water Cellular Membrane Protects the cell and allows movement across its barrier Nuclear Membrane Barrier around the nucleus, allows exchanges with the rest of the cell Genetic material, DNA, (deoxyribonucleic acid) is found inside the nucleus. DNA contains all the information needed to manufacture proteins that have specific tasks to carry out. DNA’s shape is a double helix.

DNA is divided into segments called genes, which can be found on chromosomes. The genes present will determine which proteins a cell will manufacture. A single DNA molecule will contain thousands of genes.

Genes: A gene is a segment of DNA that contains the genetic information required to carry out a particular job. Different combinations of genes make each one of us unique (Exception: identical twins).

The number of different combinations is called the genetic diversity of a particular specie.

The nucleus of a human cell contains about 25 000 genes. This complete set of genes is called the GENOME.

What are chromosomes? Chromosomes are long strands of genetic information located in the nuclei of cells. Each chromosome is a very long molecule of tightly coiled DNA. Chromosomes are most visible during cell division when they replicate.

Structure of DNA: Each step in the helix consists of a pair of building blocks called nucleotides. A nucleotide is made up of a deoxyribose sugar, a phosphate and a nitrogen- containing base. There are 4 bases. The four bases are: Adenine, Guanine, Cytosine and Thymine (A,G,C,T).

These bases always pair together in the same way. Base pairs hold the two strands of the DNA helix together. The rules for base pairing are: A always pairs with T, C always pairs with G.

DNA and cell division: A DNA molecule is able to make a copy of itself. This is how chromosomes are copied before cell division. DNA’s ability to copy itself means that all the genetic information is passed on to new cells. DNA can make copies of itself because it is double stranded.

How? The DNA molecule “unzips” as the steps of the ladder separate and the molecule splits into two single strands. New bases from the cell move in and following the pairing rules match themselves to the bases on the single strands. Each single strand builds up into a new double strand. The new DNA molecules are identical to each other and the original DNA molecule. In humans: Every cell (except for sex cells) contains 23 pairs of chromosomes. One chromosome from each pair comes from mom and the other from dad. 22 of those pairs are numbered 1-22 and the other pair is x and y (male) or x and x (female).

Cell Division

Mitosis and Meiosis Cell division: process by which new cells are produced for the purpose of growth, tissue repair and sexual reproduction.

•1.Mitosis: -division of somatic (body) cells For growth and tissue repair Diploid cells (contain 2 copies of each chromosome)

•2.Meiosis -division of gametes (sex cells) For sexual reproduction Haploid cells (contain 1 copy of each chromosome)

•MITosis takes the cell and Makes It Two (diploid)

•Meiosis has to do with sex

•From the cell’s point of view: •mITosis results in Identical Twins •mEioSis results in Egg and Sperm (haploid)

Chromosome structure

Composed of DNA and protein (histones) all tightly wrapped up in one package Duplicated chromosomes are connected by a centromere

Phases of Mitosis

•Interphase* •Prophase •Metaphase •Anaphase •Telophase

*note: Interphase occurs just before Mitosis begins. During this stage, the cell increases in size and DNA has replicated in the nucleus of the cell.

After Mitosis: Cytokinesis: The actual splitting of the identical cells into two separate cells is called cytokinesis.

Mitosis results in two diploid daughter cells, each identical to the parent cell.

Meiosis

Meiosis is only seen in the gametes (i.e. the sperm and eggs) of sexually reproducing organisms.

The stages of meiosis can be broken down into two main stages, Meiosis I and Meiosis II

Meiosis I can be broken down into four substages: Prophase I, Metaphase I, Anaphase I and Telophase I.

Meiosis II can be broken down into four substages: Prophase II, Metaphase II, Anaphase II and Telophase II

It is important to note that during meiosis, the cell splits twice. At the end of Telophase II, cytokinesis reaches completion, creating four haploid daughter cells.