DNA Structure and Replication

DNA structure

deoxyribonucleic acid DNA

store of genetic information

building blocks of DNA are nucleotides

each nucleotide made up of 3 components - phosphate-sugar-base

4 types of nucleotide bases in DNA

Adenine

Thymine

Guanine

Cytosine

A T G C

DNA strand

sugar and phosphate molecules form the backbone of DNA Molecule

bases act as side chains/groups

DNA is double stranded

chromosomal DNA consists of two paired strands of DNA twisted in helical structure

type of chemical bonding in DNA

strands are paired by formation of hydrogen bonds between bases of nucleotides

Adenine bonds with Thymine

Guanine bonds with Cytosine

function of DNA

DNA is code from which all of the proteins in the body are made

gene

the sequence of nucleotides that codes for a protein

each set of three nucleotides in a gene codes for one amino acid which is the building block of a protein

transcription

a copy of the gene is made into messenger RNA

Translation

mRNA is translated into an amino acid sequence

chromosomes

DNA is stored as chromosomes

DNA molecules are tightly packed around proteins called histones to make structures called chromosomes

how many chromosomes are in human beings?

23 pairs of chromosomes in every cell

which makes 46 chromosomes in total

sex chromosomes / autosomes

determine whether you are male XY or female XX

karyotype

a photograph of a person’s chromosomes arranged according to size

largest chromosome

chromosome 1 which contains 8000 genes

smallest chromosome

chromosome 21

it should be number 22 but scientists made a mistake when numbering)

human genome project

determined the order of bases on all 23 pairs of human chromosomes

the project took 13 years and was completed in 2003

over 20k genes were identified in DNA but the function of all of them not yet known

only 3% of our DNA is made up of genes

remaining 97% is still unclear but some are involved in regulating genes

DNA replication

DNA is copied prior to cell division

the double helix unwinds and a new strand is synthesised opposite each of the original strands

the process involves many enzymes and proteins

DNA polymerase is the enzyme that assembles a new parent strand in the proper base sequence determined by the original strand

DNA Polymerase

the enzyme that assembles a new parent strand in the proper base sequence determined by the original strand

polymerase chain reaction

a method of replicated DNA outside of the cell

small amounts of DNA can be copied with the aid of a DNA polymerase enzyme

each cycle of the technique results in the doubling of the DNA and within a few hours, 30 cycles can multiply DNA a billion fold

performed in a programmable heating block called a DNA thermal cycler

where does PCR take place?

performed in programmable heating block called a DNA thermal cycler

small reaction tubes containing DNA, nucleotides and enzymes are placed into holders