Download DNA, Transcription Translation

Today:
The Structure of a DNA Molecule:
•DNA Structure &
Function (InClass 5)
Reminder: Turn in InClass 4! (You can check
for missing work on
Angel!)
Semiconservative
DNA
Replication:
This model allows each strand to serve as a
TEMPLATE for synthesis of a new strand and is a
SEMICONSERVATIVE MODEL (each daughter
molecule will have one “parent” strand and one
newly synthesized strand).
Catching &
Repairing Mistakes
DNA Polymerases err at
a rate of 1/10,000 base
pairs.
“Proofreading”
reduces the error rate
to 1/1 billion base pairs.
Cells can repair many
errors; Humans have
130 known DNA repair
enzymes!
new
old
old
The ability to repair
damaged DNA is critical to
long-term survival.
Individuals with xeroderma
pigmentosum produce
defective repair enzymes.
Without these repair
enzymes, mutated DNA in
skin cells (UV) is not
repaired, leading to skin
cancers.
1
Getting From a Gene to a Polypeptide
Next…
1. TRANSCRIPTION:
transcribing DNA into RNA
What do cells
DO with their
DNA.??
2. TRANSLATION:
translating RNA into an
amino acid sequence
DNA
RNA vs DNA
RNA
PROTEIN
In order to
translate DNA
(RNA) you
must first crack
the genetic
“code”!
The Genetic Code
A group of three
bases (a
codon) codes
for a particular
amino acid.
2
TRANSCRIPTION
occurs in 3 Steps:
1. Initiation
(promoter)
Arabidopsis thaliana C24
wild type (left) and
transformed (GFP; right)
2. Elongation (RNA
Polymerase)
Tobacco plant expressing a
firefly gene (luciferase)
and
Herman, at right, is the first transgenic
dairy animal engineered to make the
human milk protein, lactoferrin,
which is an antibacterial protein that
can be used to treat
immunosuppressed patients and
could be incorporated into infant
formula.
3. Termination
Let’s Watch:
http://www.dnai.org/lesso
n/go/19436/15510
Translation:
The Players
Pre-mRNA
must be
EDITED…
RIBOSOMES are
Enzymes that
“Read” the mRNA
1. Ends are
capped and
tailed.
tRNA’s (transfer
RNA’s) deliver the
correct amino
acid specified by
the mRNA
2. INTRONS cut
out.
TRANSLATION also occurs in 3 steps:
1.
2.
3.
Initiation- the RIBOSOME assembles
on the mRNA molecule at the START
CODON
Elongation- the polypeptide chain is
assembled sequentially as amino
acids are covalently bound to one
another
Termination- the Ribosome reaches a
STOP CODON and releases the
mRNA and Polypeptide
Translation
3
Understanding Gene Mutations
The Whole
Story!
You Try: Part 1
Understanding Gene Mutations
1. Base-pair SUBSTITUTIONSWhat happens if UCA UCC ?
You Try: Part 2
Sickle Cell Disease: a Substitution
1. Base-pair SUBSTITUTIONSWhat happens if UAC UAG ?
The Effects:
Understanding Gene Mutations
2. INSERTIONS and DELETIONS
One+ base pairs are inserted or deleted
from a DNA sequence.
Insertions and Deletions frequently result in
FRAMESHIFT MUTATIONS.
Example: CCR5 and HIV/Plague
Resistance!
4
Lab This
Week: Two
Big Ideas
The Focus of Our PCR…
The
Polymerase
Chain
Reaction
(PCR)
Lab This
Week: Two
Big Ideas
Small
Volumes
Require
Accuracy!
5