experiments on dna we did this yesterday. (or at least tried) what to do with the post-it. on the...
TRANSCRIPT
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”