GHSGT REVIEW DNA RNA Protein Synthesis Mutations

DNA

Structure of DNA DNA is made up of small repeating units called nucleotides. Nucleotides are made of 3 parts: 1.Deoxyribose Sugar 2.Phosphate Group 3.Nitrogen Base –Adenine (A) –Guanine (G) –Cytosine (C) –Thymine (T)

Watson & Crick discovered that DNA is in the shape of a double helix where 2 strands are wrapped around each other like a spiral staircase. If we think of DNA as a twisted ladder then the sugar & phosphate make up the sides and the bases make up the rungs. Bases are held together by hydrogen bonds.

DNA Base Pairing Chargaff’s Rules- he discovered that in any sample of DNA, the amount of A=T and the amount of C=G. This means that adenine always pairs with thymine and cytosine pairs with guanine. Ways to remember – Auburn Tigers – Columbus Georgia

A pairs with T C pairs with G

Example 1: C G C T A A G T G C G A T T C A Example 2: A T C C T G A C G

DNA Replication DNA Replication- process by which DNA copies itself. – Occurs in the nucleus – Occurs during S phase of interphase

An enzyme called helicase unzips the DNA by breaking the hydrogen bonds that hold the bases together.

The site where separation and replication occur are called replication forks. DNA polymerase is an enzyme that brings in the complimentary nucleotides

Example of Replication Original DNAC G T A G A C T New DNA Original DNAG C A T C T G A

RNA & Protein synthesis

Structure of RNA Is single stranded Is found in the nucleus & cytoplasm Is made of nucleotides – Ribose Sugar – Phosphate Group – Nitrogen Base Adenine (A) Cytosine (C) Guanine(G) Uracil (U)

Three Types of RNA

RNA Transcription Messenger RNA (mRNA)- is made in the nucleus during the process of transcription. Only ½ of the DNA is used When RNA forms – C pairs with G – A pairs with U

Example of Transcription DNAC G C T A A G T G C G A T T C A mRNA_ _ _ _ _ _ _ _ Once the mRNA is made- it leaves the nucleus and goes to the ribosomes.

Translation Occurs at the ribosomes. It translates the mRNA message into a protein. You look up CODONS on the genetic code chart – Codons are groups of 3 bases on mRNA The chart tells you which amino acid would be added.

THE GENETIC CODE CHART

Translation Transfer RNA (tRNA) is like an interpreter. It brings in the correct amino acid. The bases on tRNA are complimentary to the bases on mRNA EX: mRNAAUG UCG ACC tRNA_ _ _ _ _ _ _ _ _ amino acids____ _____ _____

Protein Synthesis

Mutations

What are mutations? Sometimes cells can make mistakes when copying their DNA. These mistakes are called mutations. Mutations- are changes in the DNA sequence that affects the genetic information Mutations that occur in sex cells can be inherited.

Gene Mutations Mutations that affect one single gene or protein. There are two types of gene mutations: point and frameshift

Point Mutations Point Mutations occur at one nucleoltide and only affect one amino acid. – Ex: Substitution- one nucleotide is substituted for another one – this may or may not change the resulting amino acid

Frameshift Mutations Frameshift mutations occur when a nucleotide is added or deleted. This affects every amino acid that comes after the mutation. – This will alter the protein so that it does not carry out its normal function

Frameshift Mutations Ribosomes read in 3 letter codons THE FAT CAT ATE THE RAT Look how the ribosome would read this sentence if the “H” in the first “the” was deleted. TEF ATC ATA TET HER AT

Chromosomal Mutations Chromosomal Mutations- Changes in the number or structure of chromosomes These are much worse than single gene mutations (because it affects lots of genes)

Deletion – Occurs when part of a chromosome is missing or lost Duplication – Occurs when part of the chromosome is repeated or doubled

Inversion – Occurs when the parts of the chromosome are reversed Translocation – Occurs when two chromosomes exchange parts (one chromosome breaks off and attaches to another)

Mutagens Mutagens are chemical or physical agents in the environment that may cause mutations. – Examples: pesticides, tobacco smoke, environmental pollutants, x-rays, uv light.

Effects of Mutations Some or most have no effect- they are considered neutral some have a negative effect – Can result in genetic disorders (like sickle cell) – Can result in cancer

Effects of mutations Some have a positive effect – Altered proteins may help organism in changing environments Insects- may help them gain resistance to insecticides Humans- may increase bone density Plants- Polyploidy (extra sets of chromosomes makes the plants larger and stronger)

Mutations are important to evolution Mutations are the source of genetic variability Mutations that occur in the gametes (sex cells) are really important – Are passed on to the next generation – Affect the gene that the mutation occurred in