Download Biology 12 DNA Functions Functions of DNA: 1. To replicate or make

Biology 12
DNA Functions
Functions of DNA:
1. To replicate or make copies of itself. This occurs so that genetic information may be passed on from cell to
cell and generation to generation.
2. Control the activities of the cell. Through protein synthesis, proteins (eg. enzymes, hormones, building materials)
are made that produce phenotypic characteristics of an individual.
3. Mutate. Mutations to DNA alter proteins synthesized. May create genetic disease, some mutations create
advantageous variations in individual (selected by natural selection)
DNA Replication: Steps
1) DNA unzips - hydrogen bonds between base pairs are broken by special enzymes.
2) New complementary DNA nucleotides (present in nucleus) attach to each 1/2 of DNA strand.
Base pairs join by hydrogen bonding
3) Adjacent nucleotides join - phosphate to sugar - forming sides of DNA ladder 2 identical DNA molecules
are produced
Final Result:
Two identical DNA molecules are produced, this allows exact DNA copies to be incorporated
into new daughter cells
DNA replication occurs during cell division
Protein Synthesis:
DNA controls the production of proteins in the cell. The DNA is found in the nucleus and carries the codes for
the construction of the proteins. A section of DNA that contains the code to produce 1 polypeptide is called a gene.
The construction of a polypeptide will take place in the cytoplasm. There are two stages in the process of
protein synthesis:
A. Transcription
Summary: occurs in the nucleus where a messenger RNA (mRNA) molecule is made on a template of an exposed
side of a DNA molecule (gene). The mRNA molecule actually transcribes the codes for the construction of protein.
B. Translation
Summary: Amino acid sequence is determined by mRNA template made from DNA.
Steps:
3. mRNA travels to a ribosome site in the cytoplasm where the code is used to make a polypeptide chain.
(3 bases on mRNA called a codon)
4. tRNA brings amino acids to the ribosome. (3 bases on tRNA called an anticodon). Anticodons match with
codons. Amino Acids link through peptide bonds.
5. ribosome travels down mRNA, tRNA’s continue to bring amino acids to the growing polypeptide chain.
Production of polypeptides occurs in the cell as mRNA is translated. More than 1 ribosome can be used in this process.
Polypeptides can be produced quickly.
Mutation:
A change in the base pairs of DNA eg. by deletion or insertion of base pairs.
May be:
1. Gene mutation - small scale, affects that gene only.
2. Chromosomal mutation - larger scale, affects many genes on chromosome.
Effects of Mutation:
Mutations may cause changes in mRNA made during transcription and so may change amino acid sequence of
polypeptide produced during translation.
Example- sickle cell anemia - change in one base pair of gene causes one amino acid substitution in hemoglobin
quaternary polypeptide . Therefore, hemoglobin is abnormal and causes red blood cells to take on sickle shape
during periods of low oxygen concentration.
Environmental Mutagens: causes mutations in humans
1. Chemicals like benzopyrine in tobacco smoke (including second hand smoke)
2. Radiation - UV light and X rays
Biotechnology:
Recombinant DNA - combining DNA from 2 or more organisms.
Uses: Know 3
1. Clone genes
2. Produce human proteins (growth hormone, insulin)
3. Produce antigenic proteins (surface features) to produce safe vaccines.
4. Produce frost resistant crops.
5. Produce animal hormones example - bovine growth hormone (bGH)
6. Enhance naturally occurring bacteria for use in environmental cleanup
Using Viral Vectors to Produce Recombinant DNA (add genes to bacteria)