1. Gene Expression
How proteins are made.

2. what monomers make up proteins? G E H
what monomers make up proteins?
what monomers make up nucleic acids (DNA and RNA)?

3. Nucleic Acids Proteins Primarily DNA, RNA
Thousands of different proteins
Made up of four different bases
Made up of more than than 20 amino acids
So, how does relatively simple-sounding DNA contain the information for building thousands of different proteins?

4. codes for these amino acids:
Codons
A “codon” is a sequence of three bases in DNA and RNA. Each codon codes for a different amino acid.
This mRNA strand:
codes for these amino acids:
met
cys
glu
leu
trp

5. The Genetic Code
All 20 amino acids are coded for. Redundancy of codes is one protection against mutations.

6. The Gene Concept
A “gene” is a segment of DNA that codes for a specific protein.
Only one side of the DNA double-helix (the “sense” or “coding” strand) contains the actual gene.
Genes are defined by promotor and terminator sequences in the DNA.

7. Eukaryotic gene structure
exons
DNA
promoter
introns
A typical eukaryotic gene consists of sequences of DNA called
exons, which code for the amino acids of a protein (medium blue),
and intervening sequences called introns (dark blue), which do
not. The promoter (light blue) determines where RNA polymerase
will begin transcription.

8. A small protein is 30 amino acids long
A small protein is 30 amino acids long. How many nucleotides are needed to code for it? 30 60 90
Depends on which amino acids.

9. The same protein that is 30 amino acids long needs how many codons to code for it?60 90
Depends on the amino acids it is made of.

10. Transcription DNA stays in the nucleus.
To get information out of one gene on a strand of DNA, the gene must be transcribed.
An mRNA copy of a gene leaves the nucleus, so the original information (DNA) remains intact in the nucleus.

11. RNA RNA is a single-stranded nucleic acid.
RNA contains the bases adenine, uracil, guanine, and cytosine.
RNA contains the sugar ribose in its sugar-phosphate backbone.

13. Which of these is TRUE about RNA: RNA has uracil instead of thymine. K T G E H
Which of these is TRUE about RNA:
RNA has uracil instead of thymine.
RNA is a protein.
RNA is a single strand instead of a double-helix.
RNA never leaves the nucleus.

14. Notice that transcription takes place in the nucleus.
gene
DNA
Transcription of the
gene produces an
mRNA with a
nucleotide sequence
complementary to one
of the DNA strands.
(nucleus)
(cytoplasm)
(a) Transcription
messenger
RNA
Notice that transcription takes place in the nucleus.
ribosome
protein

15. (a) Initiation
DNA
gene 1
gene 2
gene 3
RNA
polymerase
DNA
promoter
RNA polymerase binds to the promoter region of DNA near the
beginning of a gene, separating the double helix near the
promoter.

16. (b) Elongation
RNA
DNA template strand
RNA polymerase travels along the DNA template strand (blue),
catalyzing the addition of ribose nucleotides into an RNA
molecule (pink). The nucleotides in the RNA are complementary
to the template strand of the DNA.

17. (c) Termination
termination signal
At the end of a gene, RNA polymerase encounters a DNA
sequence called a termination signal. RNA polymerase detaches
from the DNA and releases the mRNA molecule.

18. (d) Conclusion of transcription
mRNA
After termination, the DNA completely rewinds into a double helix.
The RNA molecule is free to move from the nucleus to the
cytoplasm for translation, and RNA polymerase may move to
another gene and begin transcription once again.

19. RNA synthesis and processing in eukaryotes
DNA
transcription
initial
RNA transcript
add RNA cap and tail
cap
tail
introns
cut out
and
broken
down
RNA splicing
completed
mRNA
to cytoplasm for translation
RNA polymerase transcribes both the exons and introns, producing a long
RNA molecule. Enzymes in the nucleus then add further nucleotides at the
beginning (cap) and end (tail) of the RNA transcript. Other enzymes cut out
the RNA introns and splice together the exons to form the true mRNA, which
moves out of the nucleus and is translated on the ribosomes.

20. gene
RNA
molecules
DNA
direction of transcription

21. Transcription begins when:
RNA polymerase finds a start codon
RNA polymerase finds a promoter sequence
RNA polymerase finds a ribosome

22. Base-pair matching, DNA mRNA
DNA (ns)
DNA (sense)
mRNA A G T C T A C G A U T A G C C G A U

23. The enzyme that assembles RNA bases to make mRNA is: _________________ W O R K T G E H
The enzyme that assembles RNA bases to make mRNA is: _________________
This enzyme begins reading DNA at the ____________ sequence of a gene and ends at the ___________ sequence.
True or False: The entire DNA strand must be “unzipped” for transcription to take place.
RNA Polymerase
promoter
terminator

24. Translation
Once the gene has been transcribed into mRNA, the message must be translated to build a protein.
Ribosomes (made of rRNA) “read” the mRNA message and use the information to assemble amino acids.

25. gene
Notice that translation takes place outside the nucleus, at the ribosomes.
DNA
(nucleus)
(cytoplasm)
messenger
RNA
Translation of the mRNA
produces a protein
molecule with an amino
acid sequence determined
by the nucleotide
sequence in the mRNA.
(b) Translation
ribosome
protein

26. The players:
mRNA: Carries the encoded instructions for building a protein.
Ribosome (rRNA & protein structures): these act like enzymes to catalyze protein assembly.
tRNA: Transport RNA molecules that carry amino acids from the cytoplasm to the ribosome.

27. To what class of molecules does tRNA belong?
Proteins
Carbohydrates
Lipids
Nucleic acids
Depends on which amino acid it carries.

28. W O R K T G E H
What other molecule have we encountered has active sites and acts as a catalyst? How is a ribosome like this molecule? How is it different?

29. Initiation:
amino acid
met
methionine
tRNA
initiation
complex
small
ribosomal
subunit
A tRNA with an attached methionine amino acid binds to a
small ribosomal subunit, forming an initiation complex.

30. Initiation:
met
tRNA
mRNA
The initiation complex binds to an mRNA molecule.
The methionine (met) tRNA anticodon (UAC) base-pairs
with the start codon (AUG) of the mRNA.

31. Initiation:
second tRNA binding site
catalytic site
met
first tRNA
binding
site
large
ribosomal
subunit
The large ribosomal subunit binds to the small subunit.
The methionine tRNA binds to the first tRNA site on
the large subunit.

32. Elongation:
catalytic site
met
val
The second codon of mRNA (GUU) base-pairs with the
anticodon (CAA) of a second tRNA carrying the amino acid
valine (val). This tRNA binds to the second tRNA site on the
large subunit.

33. Is this hydrolysis or dehydration synthesis?
Elongation:
met
peptide
bond
val
The catalytic site on the large subunit catalyzes the
formation of a peptide bond linking the amino acids methionine
and valine. The two amino acids are now attached to the tRNA
in the second binding position.
Is this hydrolysis or dehydration synthesis?

34. Elongation:
catalytic site
initiator
tRNA detaches
met
val
ribosome moves one codon to right
The “empty” tRNA is released and the ribosome moves down
the mRNA, one codon to the right. The tRNA that is attached to
the two amino acids is now in the first tRNA binding site and
the second tRNA binding site is empty.

35. Elongation:
catalytic site
met
val
his
The third codon of mRNA (CAU) base-pairs with the
anticodon (GUA) of a tRNA carrying the amino acid histidine
(his). This tRNA enters the second tRNA binding site on the
large subunit.

36. Elongation:
met
val
his
The catalytic site forms a new peptide bond between valine
and histidine. A three-amino-acid chain is now attached to
the tRNA in the second binding site. The tRNA in the first site
leaves, and the ribosome moves one codon over on the mRNA.

37. Termination:
met
val
his
arg
completed
peptide
arg
ile
stop codon
This process repeats until a stop codon is reached; the mRNA
and the completed peptide are released from the ribosome,
and the subunits separate.

38. The ribosome has just bonded a series of amino acids into a chain
The ribosome has just bonded a series of amino acids into a chain. What has it built?
An amino acid.
A protein.
A nucleic acid.
Impossible to tell at this point.

39. W O R K T G E H
When a tRNA leaves the ribosome, it goes off and finds another amino acid in the cell. Where do amino acids in human cells originally come from? Where do they come from in plant cells?

40. gene (a) DNA etc. complementary DNA strand template DNA strand etc.
codons
(b) mRNA
etc.
anticodons
(c) tRNA
etc.
amino acids
(d) protein
etc.
methionine
glycine
valine

41. direction of transcription
RNA
polymerase
DNA
mRNA
protein
ribosome

42. DNA (Sense) mRNA Amino Acids DNA to mRNA to Protein T A C G A
methionine
(start) U G C C
proline A U C
serine U U

43. DNA (Sense) mRNA (sense) Amino Acids DNA to mRNA to Protein C A G
valine U U A
threonine C U U
stop codon G A

44. Practice Transcription and Translation:

45. Translation begins when:
The ribosome finds a promoter sequence.
The ribosome finds a start codon.
The ribosome breaks apart.

46. The role of the ribosome is:
Interpret mRNA and build proteins.
Construct mRNA.
Replicate DNA.
Facilitate cell division.

47. The role of tRNA is: Transcribe DNA and move mRNA out of the nucleus.
Bind to the ribosome and mRNA chain together.
Carry amino acids to the ribosome.
Replace T with U when transcribing mRNA.

48. If genes code for proteins, what codes for enzymes?
Non-coding DNA
Other proteins
Nothing. They’re manufactured in the smooth ER.

49. W O R K T G E H
Write out the mRNA strand that would be formed from this DNA segment: C A T A T G G G C T T A T A C
If the segment doesn’t include the start or stop codon, how many amino acids does it code for?

50. W O R K T G E H
Suppose a segment of DNA contains the triplet ACG, and a mutation changes it to ACT. Would that cause a change in the resulting amino acid chain? Use your knowledge of transcription and translation to find the answer.

51. Gene Regulation
All cells in the human body have the same DNA and the same set of genes, yet different cells look different and do different jobs.
Cells have systems to regulate which genes are “turned on” (transcribed) and which are not.

52. Cells can control the frequency of transcription. Different mRNAs
DNA
1 transcription
rRNA
+ proteins
pre-mRNA
tRNA
Different mRNAs
may be produced
from a single gene.
2 mRNA
processing
Cells can control the
stability and rate of
translation of
particular mRNAs.
ribosomes
mRNA
tRNA
amino
acids
If the active
protein is an
enzyme, it
will catalyze
a chemical
reaction in
the cell.
3 translation
inactive
protein
Cells can regulate
a protein’s activity
by degrading it.
4 modification
substrate
active
protein
product
Cells can regulate
a protein’s activity
by modifying it.
5 degradation
amino
acids

53. (a) Structure of the lactose operon
codes for
repressor protein
operator: repressor
protein binds here R P O
gene 1
gene 2
gene 3
promoter: RNA
polymerase
binds here
structural genes that code for
enzymes of lactose metabolism
The lactose operon consists of a regulatory gene, a promoter, an
operator, and three structural genes that code for enzymes
Involved in lactose metabolism. The regulatory gene codes for a
protein, called a repressor, which can bind to the operator site
under certain circumstances.

54. (b) Lactose absent
RNA
polymerase
transcription blocked R P
gene 1
gene 2
gene 3
repressor protein
bound to operator,
overlaps promoter
free repressor
proteins
When lactose is not present, repressor proteins bind to the
operator of the lactose operon. When RNA polymerase binds to
the promoter, the repressor protein blocks access to the structural
genes, which therefore cannot be transcribed.

55. (c) Lactose present
RNA polymerase binds
to promoter, transcribes
structural genes R O
gene 1
gene 2
gene 3
lactose-
metabolizing
enzymes
synthesized
lactose bound
to repressor proteins
When lactose is present, it binds to the repressor protein. The
lactose-repressor complex cannot bind to the operator, so
RNA polymerase has free access to the promoter. The RNA
polymerase transcribes the three structural genes coding for
the lactose-metabolizing enzymes.

56. Recap
Transcription moves coded information from DNA to the ribosome by creating an mRNA copy of a gene.
In translation, a ribosome “reads” the mRNA code and uses the information to assemble a chain of amino acids to make a protein.