Chapter 17: From Gene to Protein
Key Concepts
17.1 – Genes specify proteins via transcription and translation
17.2 – Transcription is the DNA-directed synthesis of RNA: a closer look
17.3 – Eukaryotic cells modify RNA after transcription
17.4 – Translation is the RNA-directed synthesis of a polypeptide: a closer look
17.5 – RNA plays multiple roles in the cell: a closer look
17.6 – Comparing gene expression in prokaryotes and eukaryotes reveals key differences
17.7 – Point mutations can affect protein structure and function
Interactive Questions
Interactive Question 17.1
Fill in the sequence in the synthesis proteins. Put the name of the process above each
arrow.
DNA → RNA → protein (polypeptide)
Interactive Question 17.2
Practice using the dictionary of the genetic code in your textbook. Determine the amino
acid sequence for a polypeptide coded for by the following mRNA transcript. (written
5’→3’):
AUGCCUGACUUUAAGUAG
Met-Pru-Asp-Phe-Lys-STOP
Interactive Question 17.3
Review the key steps of transcription in eukaryotes:
a. Initiation – Trans-factors bind to promoter and help RNA polymerase II bind
DNA helix is unwound, hydrogen bonds sequenced.
b. Elongation – RNA polymerase moves along the DNA, mRNA increases in length
nucleotides are added on 3’ end.
c. Termination – RNA polymerase transcribes past the termination signal and poly
A tail.
Interactive Question 17.4
How does the mRNA that leaves the nucleus differ from the primary transcript premRNA?
A modified 5’ cap has a GTP added.
- Poly A tail is added (250 nucleotides).
- Introns are cut out by splicesome.
- Exons are attached together.
Interactive Question 17.5
Using some of the codons and the amino acids you identified in Interactive Question
17.2, fill in the following table.
RNA Triplet 3’→5’
TAC
GGA
TTC
ATC
mRNA Codon
5’→3’
AUG
CCU
AAG
UAG
Anticodon 3’→5’
Amino Acid
UAC
GGA
UUC
AUC
Methionine
Protive
Lysine
STOP
Interactive Question 17.6
1.
2.
3.
4.
Codon Recognition
Peptide Bond Formation
Translation
Termination
a. growing polypeptide chain
b. tRNA with amino acid
c. large subunit of ribosomes
d. A site
e. small subunit
f. 5’ end mRNA
g. peptide bond formation
h. E site
i. release factor
j. termination codon
k. P site
l. free polypeptide
Interactive Question 17.8
Fill in the functions for the following types of RNA molecules
a.
b.
c.
d.
e.
mRNA – Carries the code from DNA that specifies the amino acid
tRNA – Carries a specific amino acid to its position in a polypeptide
rRNA – Plays catalytic (ribozyme) roles and structural roles in ribosomes
snRNA – Small nuclear RNA, part of the spliceosomes, splices mRNA
SRP RNA – Signal recognition particle that binds to signal peptides bound to
endoplasmic reticulum
f. snoRNA (small nucleolar RNA) – Aids in processing pre-RNA transcript in
nucleolus
g. siRNA (small interfering RNA) and miRNA (microRNA) – small interfering
RNA
Interactive Question 17.9
Define the following, and explain what type of point mutation could cause each of these
mutations.
a. silent mutation – A base pair substitution that produces a codon that still codes for
the same amino acid
b. missense mutation – Base pair substitution or frameshift mutation that results in a
codon for a different amino acid
c. nonsense mutation – Base pair substitutions or frameshift mutation that creates a
stop codon and prematurely terminates translation
d. frameshift mutation – An insertion or deletion of one, two, or more, than three
mucleotides that disrupts the reading frame and creates extensive missense or
nonsense mutations
Structure Yo’ Knowledge
1.
Template
Location
Molecules involved
Enzymes involved
Control – start and stop
Product
Product processing
Energy source
Transcription
DNA
Nucleus (eukaryotes)
RNA nucleotides, DNA
template strands, RNA
polymerase, transcription
factors
RNA polymerase,
ribozymes
Transcription factors,
TATA box, poly A
Primary transcript (premRNA)
RNA processing: 5’ cap,
poly A tail, splicing
RIbonucleoside,
triphosphate
Translation
RNA
Cytoplasm
Amino acids, tRNA,
mRNA, ribosomes, ATP,
GTP, enzymes, initiation
elongation
Aminoacyl-tRNA
synthetase
Initiation factors, AUG,
stop codons, release factors
Protein (polypeptide)
Spontaneous folding,
disulfide bridges, cleaving,
structure
ATP, GTP
2. The genetic code is the RNA triplets that code for amino acids. The order of these
codons is specified by the sequence of nucleotides on DNA, which is transcribed into the
codons found on mRNA and translated into their corresponding amino acids. There are
64 possible mRNA codons created from the our nucleotides used in the triplet code (43)
Redundancy of the code refers to the fact that several triplets may code for the same
amino acid. Often these triplets differ only in the third nucleotide. The wobble
phenomenon explains the fact that there are only about 45 different tRNA molecules that
pair with the 61 possible codons (three codons are always stop codons). The third
nucleotide of many tRNAs can pair with more than one base. Because of the redundancy
of the genetic code, these wobble tRNAs still place the correct amino acid in position.
3.
POINT MUTATIONS
base-pair
substitutions
may have
may be
may be
due to
insertions
or deletions
spontaneous
small effect
on protein
usually have
during
due to
large effect
on protein
DNA repair,
replication,
recombination
redundancy
of code
depends on
properties of
replacement
amino acid
called
silent
mutation
called
may be
chemical,
physical
if
location of
replacement
amino cid
whether in
active site
missense
mutation
mutagens
create stop
codon
called
nonsense
mutation
such as
base analogs,
X-ray, UV
Test Yo’ Knowledge
1. d – ornithine or citrulline (p. 310)
2. a – DNA to RNA (p. 311)
3. b – CAU (p. 314)
4. e – begins transcription at a promoter sequence and moves along the template
strand of DNA, elongating an RNA molecule in a 5’ 3’ direction. (p. 316)
5. c – It depends on the orientation of the RNA polymerase, whose position is
determined by particular sequences of nucleotides within the promoter.
6. b – RNA polymerase (p. 328)
7. c – Assemblies of protein and snRNPs, called spliceosomes, may catalyze
splicing. (p. 328)
8. c – snRNA (p. 319)
9. b – 200 (p. 339)
10. a – exons (p. 320)
11. d – Introns provide more area where crossing over may occur and thus increase
the probability of exon shuffling between alleles. (p. 316)
12. d – an RNA molecule that functions as an enzyme. (p. 323)
13. d – snRNA (p. 317)
14. c – gene for transcription factor (p. 314)
15. b – binds to its specific amino acid in the active site of an aminoacyl-tRNA
synthetase (p. 328)
16. e – 5-4-2-1-3 (p. 324)
17. e – all of the above (p. 329)
18. b – rRNA (p. 320)
19. b – It lines up in the 5’3’ direction along the 5’3’ mRNA strand. (p. 317)
20. a – the addiction of sugars or lipids in certain amino acids. (p.310)
21. a – the action of several ribosomes in a string, called a polyribosome. (p.313)
22. d – would be the first 20 or so amino acids of a protein destined for a membrane
location of secretion from the cell. (p.315)
23. e – all of the above (p. 323)
24. b – The substitution must involve three nucleotide pairs, otherwise the reading
frame is altered. (p. 318)
created by doo lim