CHAPTER 11: GENE
EXPRESSION
Cells use
information in
genes to build
several
thousands of
dif ferent
proteins, each
with a unique
function. But
not all proteins
are required by
the cell at any
one time. By
regulating
gene
expression,
cells are able
to control when
each protein is
made.
Role of Gene Expression
-activation, or “turning on” of a gene that
results in transcription and production of
mRNA
What Occurs During Transcription?
Somewhat similar to DNA replication
Strands must separate
Enzymes and energy are required
Also quite different from DNA replication
Only one gene on one strand is transcribed
Different enzyme is used
RNA Polymerase (RNAP)
What Occurs During Transcription? cont.
Initiation – Proteins called transcription factors
attach to the beginning of the gene
Called the promoter region
Signal where RNAP should bind
1. What Happens During RNA Processing?
2. Eukaryotic DNA can be divided into two main
parts
3. Introns – sequences of DNA that do not
become proteins
4. Introns interrupt genes
4. Can be between genes or within one gene
3. Exons – sequences of DNA that become
proteins
4. Exons are expressed
FUN FACTS!
2 % of your DNA actually codes for
Only ____
protein!
We used to think the other98____% was “junk
DNA”
We now think that most of that DNA plays a
role in
7 regulating gene expression
Only ____% is now thought to be non-coding
DNA
1. What Happens During RNA Processing?
2. Both introns and exons are transcribed
3. Only exons are used to make proteins
4. Introns must be spliced (cut) out
5. Different proteins can be made
depending on the order in which
exons
are put back together
(alternative splicing)
1. What Happens … RNA Processing? cont.
2. Extra nucleotides are added to both ends of the
RNA
3. Forms a cap and tail
4. Keeps RNA stable as it “swims” out of
nucleus and into cytoplasm
5. Single-strand RNA is less stable than
double-strand DNA
There is no RNA processing in prokaryotes. RNA is
translated immediately after it is transcribed.
RNA processing only
happens in eukaryotes
Click Here!
PUT THE FOLLOWING IN ORDER FROM
LARGEST TO SMALLEST…
1. Piece of mRNA immediately after
transcription
2. Parent DNA strand that the mRNA came from
3. Gene that produced the mRNA
4. Piece of mRNA immediately prior to
translation
5. Daughter strand of DNA produced during
replication
6. One exon in the gene
A – polypeptide
chain
B – amino acid
C – tRNA
D – mRNA
A
E – small ribosomal
subunit
F – large ribosomal
subunit
B
G – anticodon
H - codon
C
G
F
D
H
E
1. What Happens During Translation?
2. RNA message is used to construct protein
2. Occurs in three main steps
3. Initiation – beginning of the process
4. Small ribosomal subunit attaches
4. Initiator tRNA binds to start codon
5. Anticodon of tRNA matches codon of
mRNA
4. Large ribosomal subunit attaches
1. What Happens During Translation? cont.
3. Elongation – constructing a polypeptide
4. Incoming tRNA binds to A site of ribosome
4. Polypeptide leaves tRNA of P site and attaches
to new amino acid on tRNA of A site
4. Old tRNA leaves
5. mRNA and new tRNA shift left which makes
room for next tRNA to bind
1. What Happens During Translation? cont.
3. Termination – the end of protein synthesis
4. Stop codon enters A site of ribosome
5. Signals end of translationSee? I tahld yoo
4. Polypeptide is released
I’d bee bahck!
4. Ribosomal subunits break apart
TRANSLATION & YOU!
TRANSLATION & YOU!
TRANSLATION & YOU!
3-D Computer Animation
Molecular Data Animation
Check Those Concepts
1. What is the difference between introns and exons?
2. What is RNA processing? What happens during this
process?
3. What are two reasons why RNA must be processed in
eukaryotes?
4. What happens during translation?
5. What role do the following play in translation: mRNA,
tRNA, amino acids, small ribosomal subunit, large
ribosomal subunit, A site, P site?
1. What Causes Mutations?
2. Mutations can involve changes to a single
gene or to an entire chromosome
2. Can be beneficial or harmful
3. Beneficial mutations lead to genetic diversity
4. Genetically diverse populations have a
greater chance of survival
4. May lead to evolution
1. What Causes Mutations? cont.
2. Gene mutations (three types)
3. Substitution – one nitrogenous base is
changed to another
4. May have no effect due to redundancy
in code
1. What Causes Mutations? cont.
3. Insertion – new nucleotide is added to existing sequence
3. Deletion – nucleotide is removed
3. Both insertion and deletion mutations result in
frameshifts
4. RNA “downstream” of the mutation is read differently
5. Creates a “domino effect”
5. Almost always create
non-functioning protein
Frameshift
FRAMESHIFTS & YOU…OR YOUR CAT
Example: | THE | FAT | CAT | ATE | THE | RAT |
If the letter “e” in THE is deleted, the letters shift
and the entire sentence now has a different
meaning
| THF | ATC | ATA | TET | HER | AT |
I’m not overweight,
I’m under-tall!
IT’S TIME FOR MATH WITH MR. J.!
3 DNA nucleotides + 3 RNA nucleotides (codon) = 1 amino acid
GGA
CCU
Proline
Are Those Concepts? Let’s Check!
1. What are the two main types of mutations?
2. What are the three different types of gene
mutations? What is the difference between them?
3. Which type of gene mutation is more serious?
Why?
4. Mutagens cause mutations. What are some
mutagens?
1. What Causes Mutations? cont.
3. Chromosomal mutations (four types)
4. Deletion – portion of chromosome is lost
4. Duplication – chromosome receives a new piece
1. What Causes Mutations? cont.
4. Inversion – portion of chromosome breaks
away and is attached in reverse order
4. Translocation – portion of chromosome breaks
away and reattaches to a different chromosome