CHAPTERS 8 & 9DNA AND PROTEIN SYNTHESIS

THE CENTRAL DOGMA

Experiments on DNA

We did this yesterday. (Or at least tried) What to do with the post-it.

On the door place the post-it based on how well you understand the results of the experiments and the basics of how they worked. Top= I’m good: Bottom=What experiments?

If you have a specific question, Write it on the post-it.

Watson and Crick DNA Model Double Helix

Twisted ladder formed of nucleotides.Rungs of the ladder are nucleotide bases.

Base pairing rule:Adenine -> Thymine : Cytosine -> Guanine

Watson and Crick continued… Sides of the ladder are alternating

deoxyribose sugars and phosphate groups

One page paper, the most important in biology since Darwin’s The Origin of Species.

DNA Replication: Semi-conservative replication (3 main steps)

1. DNA uncoils and unzips with help from Helicase (enz.) and exposes unpaired bases on 2 separate strands @ the replication fork.

2. New DNA nucleotides bond to the existing old strands with help from DNA Polymerase according to base pair rules.

3. Result: 2 New double helices formed. Each old strand paired up with a new strand.

Other DNA Replication Info After step 2, DNA “proofreads” the

strand to assure no mistakes are made. DNA Rep. takes place during S-phase of

Interphase, before cell division. DNA Rep. can only extend existing

DNA.

How DNA controls all

A trait (phenotype) is the physical expression of a gene.Ex: visible characteristics, hair, height, etc.

A gene is a length of DNA which is the code to make a protein.

A chromosome is a whole series of genes (DNA segments) linked.

The nucleus contains all the chromosomes of the cell.

The nucleus controls the cell by containing DNA. How?

The DNA determines which proteins (enz.) will be made.

The enzymes determine which activities the cell will perform.

Analogy: Boss (DNA) tells (codes) the workers (Proteins) to do their job (Function)

Linkage Group

Genes on the same chromosome inherited together.

Ex: Everywhere A goes B goes too.

Crossing Over

An exchange of genes between homologous chromosomes during meiosis when two adjacent chromosomes have parts break free and reattach themselves to the other chromosome.

Results in new genetic combinations and adds to diversity of life.

A= ShortB= Blonde HairC= Blue Eyes

a= Tallb= Brown Hairc= Brown Eyes

1

2

1= Short, Blonde Hair, Brown Eyes2= Tall, Brown Hair, Blue Eyes

Multiple Gene

More than two genes are responsible for a trait.AKA: Polygenic

Ex: Human skin color or eye color8 Genes are involved

3 Forms of RNA

rRNA- makes up part of the ribosome. tRNA- picks up specific aa in the

cytoplasm and transfers them to the working ribosome to become part of a growing protein.

mRNA- brings the DNA message into the cytoplasm where a ribosome binds to it to begin the process of translation.

DNA vs. RNADNA RNA

Deoxyribose Sugar

Thymine nucleotide base

Double Stranded

Ribose Sugar

Uracil nucleotide base

Single Stranded

Transcription

DNA uncoils and one side of the two strands is read by RNA Polymerase, which has helicase powers, to form a strand of mRNA.

The mRNA travels into the cytoplasm where ribosomes attach to it to start translation.

RNA Processing

Cap- Protective cap added to one end.

Poly A tail- add about 200-300 Adenines to the opposite end of the cap.

Splicing- cuts introns, leave exons (choose which exons to determine protein)

Translation

mRNA is read chemically by the ribosome.

In the process, tRNA is used to bring the correct aa from the cytoplasm to attach to the ribosome-mRNA complex and begin forming the protein.

The protein grows as aa brought in by the tRNA are added together in a long strand.

The tRNA bonds to a specific aa at one end and to a specific 3 base sequence on the mRNA called the codon on the other end.

This is the codon - anticodon pairing that ensures a maintenance of message from DNA to protein.

Codon- 3 consecutive mRNA bases that encode a specific aa. Cannot be 1-1 because we have 20 aa.

Understanding how DNA makes RNA Start with a strand of DNA segment and

turn it into an mRNA segment.

ATCGATGAGTGCGTAGCT = DNA Strand

UAGCUACUCACGCAUCGA =RNA Strand created

from the DNA StrandInstead of bringing in a T to pair with the

A, a U would be brought in instead. All the other base pairing combinations stay the same.

How RNA makes Protein

We need to start by knowing the different parts.

UAGCUACUCACGCAUCGA = mRNAThis needs to be broken down into 3

consecutive bases that we call a codon. UAG-CUA-CUC-ACG-CAU-CGA

This are the codon we would look up on the mRNA chart.

How the tRNA works

The tRNA contains an anti-codon stretch at one end of it’s structure. This binds to the codon on the mRNA. The tRNA anti-codon is the compliment of the mRNA.

You never look up the anti-codons on a chart.

UAG-CUA-CUC-ACG-CAU-CGA = mRNA

AUC-GAU-GAG-UGC-GUA-GCU= tRNA

Gene Expression

Prokaryotes- operon systemIts only on when its needed.Read 190-191.

Eukaryotes The same general principle as Prokaryotes.Read 192-193

Lac Operon

The operon makes the enz. LactaseLactase digests the sugar lactose

When lactose is present the operon turns on. When not, it is turned off.

Homeotic and Oncogenes Homeotic- master genes that control

embryonic development. Which parts of body from what parts

Oncogenes- genes that cause cancerWe may all have some we inherited.

“The Guardian Angel gene” p53

Anti-cancer gene and works in the following way…

1. Activates DNA repair proteins when DNA is damaged.

2. Has the ability to hold cell cycle @ G1/S phases to repair.

3. Will kill the cell if DNA is beyond repair.

RNAi- RNA Silencing

It then has the power to bind to an mRNA and can shut down any gene that was going to be translated.

Environment and Gene Expression Genes are like blueprints however on

occasion the environment alters it.

The environment can have a good or bad effect on the gene expression.

Ex: Fox’s coat turns white in winter and brown in summer.

Chromosome Mutations

Translocation- piece breaks off and joins a different chromosome

Inversion- breaks than pulls a 180.

Addition- sequence reoccurs, duplication

Deletion- lose a piece of a chromosome

Other Chromosome Mutations

Nondisjunction- a whole chromosome is in the wrong place. Homologs do not separate right during

Anaphase.

Polyploidy- a whole set of chromosome is wrong.Typically happens in plants b/c asexual.

Gene Mutations

Substitution- replace base with another

Deletion- gets rid of a baseShifts reading frame down

Addition- adds a baseShifts reading frame up

Effects of a mutation

Good/Beneficial- Arisen a new trait that aids in survival.

Bad/Harmful- Very lethal, death, short life span.

No effect or neutral- No real change visible in current environment.

Good Example

In Uganda, 15% of elephants are born without tusks. This is inherited as a mutation that prevents tusk formation.

Normally, less tan 4% are affected with his defect.

Why would this happen? Natural Selection.

Elephants with tusks get poached, so it is more favorable now to not have tusks so they don’t get shot.

Bad and Neutral

Bad: Sickle-cell anemia is an example of a bad mutation. Even though it provides some protection against malaria, the condition is not recommended. Sickle cell assaults the way the blood flows.

Neutral: Shows no effect. Most mutations are categorized as having no effect on an organism at that time.

Causes of Mutations

MutagensRadiation: UV light, X raysChemicals: mustard gas, chloroform

Transposons- Jumping GenesDiscovered by Barbara McClintockNobel Prize in 1983“Cut and paste” or “Copy and Paste”