WJEC BIOLOGY UNIT 2 TOPIC 2: DNA AND CELL DIVISION
Human chromosomes are made up of DNA and proteins. The DNA stands for deoxyribonucleic acid, but you don't really need to know that. DNA is a double helix (two interlocking spiral) formation made up of alternating sugar and phosphate. DNA contains the coded information determining the amino acid sequences which affect your inherited characteristics and your cell functioning.
A gene is a section of DNA made from a sequence of amino acids. Each amino acid is made up of 3 bases. The 4 DNA bases are:
These bases are always paired up, adenine and cytosine, guanine and thymine. These are held together by weak bonds so that it can be "unzipped" to copy the genes.
James Watson and Francis Crick are credited with the discovery of DNA.
Mitosis is a type of nuclear division used in growth or the replacement of cells. The chromosome number is constant and is genetically identical to the parent cell.
In mitosis, a cell replicates itself and then divides into 2 daughter cells.
Meiosis is a type of nuclear division used in the formation of sex cells (gametes). The chromosome number halves from 46 in the parents cell to 23 in the daughter cell. The chromosomes vary from cell to cell but they all come from that parent cell (genetic variation, remember?).
In meiosis, a cell replicates itself, splits itself in 2 and then those cells split themselves in 2, resulting in 4 daughter cells.
Other stuff you need to know:
Nerve cells suck at replacing themselves.
Blood cells are produced via mitosis in bone marrow.
Meristems = mitosis for trees
Stem cells have been used to treat certain diseases.
The size to which plants grow depends on:
The ability to support themselves in a position to absorb enough sunlight.
The maximum height to which water can be transported up the trunk or stem.
The size to which animals grow depends on:
The ability to support themselves so they can move.
The ability to get oxygen to their cells to release energy for respiration.
