All living organisms use DNA to store genetic information.
DNA contains the instructions to construct other components of the cell, such as proteins and RNA molecules.
what is DNA composed of
DNA is composed of nucleotides that form the repeating unit of each strand. Nucleotides consist of a sugar molecule, deoxyribose, a phosphate group and a nitrogenous base.
nitrogenous bases in DNA
there are 4 nitrogenous bases - adenine, thymine, guanine, cytosine
complementary hydrogen bonding
adenine always bonds with thymine on the adjacent DNA strand (A-T) via hydrogen bonds.
guanine always bonds with cytosine (G-C) via hydrogen bonds.
why are the hydrogen bonds weak
hydrogen bonds are weak so they can separate and reform easily when DNA is replicated.
what do the bonds between the strands enable
The result of the two strands connected together is that DNA forms a double helix.
ratio of A+T/G+C
each DNA molecule always contains the same amount of A as T and the same amount of G as C, but because the sequence of bases varies for each species, the ratio of A+T : G+C is always different
3' and 5' ends
5' end = phosphate
3' end = hydroxyl (OH)
what is a chromosome
chromosomes are found in the nucleus of every cell of our body and are made up of DNA, tightly coiled around proteins
DNA in Eukaryotic cells
1. DNA molecules are wound tightly around globular proteins called histones to form nucleosomes.2. Nucleosomes pack together to form chromatin.3. Chromatin is organised into linear structures called chromosomes.4. A segment of the DNA molecule that codes for a protein molecule, a polypeptide or an RNA molecule is called a gene.
what do genes determine
Genes determine what proteins are made within a cell which in turn determines the structure and function of the cell.
somatic cell chromosomes
eachorganism has the same number of chromosomes in each somaticcell (non sex cells).the number and type of chromosomesin the somatic cells of an organism is unique for each species.
how many chromosomes in humans?
46 choromsomes
homologous pair
a pair of chromosomes, one from each parent, that have relatively similar structures and gene values
when are chromosomes visible
after the DNA has been copied and the 2 copies (sister chromatids) are still attached at the centromere. DNA highly condensed in X shape.
what is a chromosome karyogram
when the chromosomes are condensed and visible a photographcan be taken. The chromosomes in the photo can be cut out, arranged in order of size, numbered and pasted to produce a composite photo called a karyogram.
what does a karyogram show
a karyogram shows a karyotype.
male and female chromosomes
male and female karyotype vary only by 1 pair of chromosome.
XX - female.
XY - male
gene locus/loci
specific location of a gene on a chromosome.
how can a chromosome be identified
a chromosome can be identified by its genes or a particular gene locus. They vary in:
1. Genes present
2. Size and shape
3. Banding pattern
DNA is the genetic material that contains instructions for building an organism.