GHSGT REVIEWDNARNA

Protein SynthesisMutations

DNA

Structure of DNA• DNA is made up of small repeating units

called nucleotides.• Nucleotides are made of 3 parts:

1. Deoxyribose Sugar2. Phosphate Group3. 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 TG 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 DNA C G T A G A C T• New DNA

• New DNA• Original DNA G 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

• DNA C G C T A A G TG 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: mRNA AUG 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