Download From Gene to Protein The Central Dogma

From Gene to Protein
The Central Dogma
GENES determine traits by building individual proteins for that trait
An
error in the gene = an error in the protein
The Central
Dogma
DNA
RNA
Amino Acid Chain
(Protein)
Figure 14.3
DNA holds the instructions,
while RNA carries out the
instructions. RNA is a lot
like DNA, except:
1. Ribose
2. Uracil
3. Single Strand
4. RNA can leave the
nucleus, thus carries the
"message"
Figure 14.5
The instructions on
mRNA (messenger
RNA) are read by the
ribosome as a series
of 3 bases called a
CODON
Each CODON
specifies one AMINO
ACID.
Some amino acids are
repeated (third base
wobble) to minimize
mutations
Figure 14.6
TRANSCRIPTION:
The process where mRNA is
made from DNA
Follows base-pair rule
has uracil instead of thymine
RNA polymerase is used to
build the strand of mRNA
Where have you heard the
term “polymerase” before?
Transcription Animations
Transcription: Stolaf.edu
Transcription: University of Nebraska
Transcription: Concord.org
Translation: process by which protein
is built from the mRNA
Occurs at the
ribosome (rRNA)
tRNA brings amino
acids to the
developing protein
chain
Each 3 bases on
mRNA (called a
codon) codes for a
single amino acid
by matching the
anti-codon on tRNA
3 bases on mRNA
= a codon
Matching 3 bases on
tRNA
= anticodon
Before translation
begins, a tRNA must
be “charged.” This
ACTIVE process
occurs when an
enzyme attaches the
appropriate amino
acid.
Translation occurs on the ribosome in a series of steps.
1- initiation: the small subunit of the ribosome bonds to the
start codon (AUG) of the mRNA. The charged tRNA (anticodon UAC) links to the start codon. The large subunit of the
ribosome attaches and the process begins. (If AUG is always
the start codon, what is always the starting amino acid?)
Translation occurs on the ribosome in a series of steps.
2- elongation: the ribosome complex moves along the mRNA
reading each codon. New, appropriately charged tRNA
molecules enter at the A site, release their amino acid to the
growing polypeptide chain at the P site, and leave (uncharged) at the E site. Note: The un-charged tRNA can be
recharged and used in later translations.
Translation occurs on the ribosome in a series of steps.
3- termination: When the ribosome reaches one of three stop
codons, the complex releases and the created polypeptide
chain begins protein folding. Note: Several ribosomes can
translate the same piece of mRNA simultaneously to boost
protein production.
amino acids
A U G
TRANSLATION (protein synthesis)
* All genes start with AUG, also called the START CODON
It attaches to anticodon UAC and the amino acid methionine.
This is the big
picture. Can
you explain it
in your own
words?
Animations of Translation
Translation: Stolaf.edu
Translation: University of Nebraska
Translation: Concord.org
Regulation of Gene
Expression
Consider that....
Every cell of the body contains ALL the DNA for the organism.
Not all genes are necessary all the time
Cells must have the ability to turn a gene on and off
ENTER: THE OPERON MODEL
OF GENE EXPRESSION
See other slides
55-57 & 61-69
Operons and Gene Control
Experiments with E. Coli showed that it is capable of
regulating the expression of its genes. Discovered prokaryote
operons
A prokaryote operon consists of the following elements
1. Promoter - gene sequence where RNA polymerase
attaches, signalling the start of the gene
2. Operator - where a repressor
binds, stopping the transcription of
that gene
3. Structural Genes - genes
coding for the enzyme, they are
transcribed as a unit
The trp Operon
It controls the production of tryptophan.
If tryptophan is already present, it binds to and activates the
repressor to prevent more tryptophan from being made
The lac Operon
In this case, the prokaryote only needs lactase when lactose is
present. This gene works in reverse of trp. The presence of
lactose deactivates the repressor and turns on the gene.
REMEMBER!
Operons are only found in prokaryotes, but gene control in
eukaryotes is similar. A little more complicated, but similar.
Repressors versus Inducers
The trp operon is a repressible operon, it is normally on but
can be turned off when tryptophan is present. A repressor
turns off a gene.
The lac operon is an inducible operon because it is normally
off but can be turned on when lactose is present. An inducer
turns on a gene.
Grammar Time
A woman is pregnant and the baby is
later. The doctor says they will "INDUCE"
labor tomorrow. What does he mean?
In eukaryotes, a
variety of
mechanisms regulate
gene expression
1. chromatin structure
2. transcriptional control
3. post transcriptional control
4. translational control
5. post translational control
Chromatin Structure
Eukaryote DNA is wound
around protein molecules
called histones. More
tightly wound regions
cannot be reached for
transcription. Less tightly
wound are more easily
accessed.
The others are pretty
self-explanatory once
you practice your
vocabulary!
BARR BODIES
In females, chromatin of one of the X chromosomes winds so
tightly that it inactivates, this inactive chromosome is called a
BARR BODY. This method of control can also be used in codominant pairs.
Barr Body in Cats
Genotype:
XB XO
The black patches are XB and the
orange patches are XO, the cat is
multicolored because not all X's are
activated
Gene Mutations
Point Mutations - single base changes, causing a
change in the amino acid structure (protein)
Frameshift mutation
1-2 bases are added or deleted, shifting all codons downstream
GAT
CAT
AAA
GAT
A CA TAA A
What happens when you have a
nonfunctional protein?
Hemophilia
PKU
Cystic Fibrosis
Etc.
Cancer and Genetics
Growth of cancer often begins with the loss of the TUMOR
SUPPRESSOR GENE (p53)
ONCOGENES activate, cell division occurs uncontrollably
Breast Cancer Gene
BRCA1 (brak-uh)