From DNA to Proteins
Chapter 13
Before you go on…
Review the answers to the following questions to test your
understanding of previous material.
1.
DNA performs two unique functions necessary for the
perpetuation of life. Briefly describe these two functions.
2.
Discuss the significance of specific base pairing in DNA
replication (and RNA synthesis).
3.
Describe the concept of a gene: where are they, what do they
do, and how are they inherited?
4.
What are mutations: what causes them, are there different
kinds, and can they be repaired?
5.
What is the relationship between the informational molecules
DNA and RNA?... between these molecules and proteins?
6.
List and describe several roles of different proteins in cells. (In
other words, why is protein synthesis important?)
Learning Objectives
1. Compare and contrast the chemical structure and function
of DNA and RNA.
2. Discuss the significance of specific base pairing in DNA
replication and in RNA synthesis.
3. Name the enzymes important in DNA and RNA synthesis.
4. Differentiate between the processes of transcription and
translation.
5. Describe the roles of the 3 different types of RNA in
protein synthesis.
6. Messenger RNA contains a start codon and a stop codon.
Why is this necessary?
7. Describe what is happening during cell differentiation and
animal metamorphosis.
8. Describe the inherited component of cancer
development? What happens?
Three Classes of RNAs
• Messenger RNA (mRNA)
p. 196
– Carries protein-building instructions
• Ribosomal RNA (rRNA)
– Major component of ribosomes
• Transfer RNA (tRNA)
– Delivers amino acids to enzymes at ribosomes, in
the order dictated by mRNA, to build correct
polypeptide
Where is RNA made? What two kinds of molecules make up a
ribosome? Where do you find ribosomes in a cell?
Transcription &
DNA Replication
•Nucleotides added
as in DNA
replication (specific
base pairing)
•Unlike DNA
replication,
only small stretch
acts as a template
•RNA polymerase
catalyzes nucleotide
addition
When is DNA replicated normally?
Name the enzyme that catalyzes the
replication of DNA.
•Product is a single
strand of RNA
p. 196
Steps from DNA to Proteins
Same two steps produce all
proteins:
1) Transcription:
•
•
•
DNA is transcribed to form mRNA
occurs in the nucleus
mRNA moves into cytoplasm
2) Translation:
•
•
translation occurs at ribosomes
(rRNA)
mRNA is translated by tRNA to
form polypeptide chains, which
fold to form functional proteins
Hopefully, nothing is
lost in translation!
DNA
to
Protein
Where might this
ribosome be in the cell?
What has yet to happen
to this polypeptide chain
(before it is a functional
protein)?
Where might this protein
be used in the cell?
DNA & RNA compared…
p. 196
DNA:
RNA:
• Double stranded
• Self replicating
• ACTG bases
• Single stranded
• Manufactured from
DNA
• ACUG bases
Match base pairs in DNA
replication: A - T
G- C
C- G
T- A
Match base pairs for RNA
synthesis:
A- U
DNA template
G- C
C- G
T- A
The “language” of Nucleic Acids
• DNA codes for amino acids in triplets:
TAC CGT AAA CGT …
• mRNA (messenger RNA): a “copy” of DNA that is read in
codons.
AUG GCA UUU GCA …
• tRNA (transfer RNA): ‘interpreter’ of mRNA using
“matching” anticodons.
AUG GCA UUU GCA …
If the recipe for
proteins only had 4
words (ACTG),
how would this
limit the variety of
proteins possible?
U A C
How many triplets are
in a gene that codes
for a polypeptide
that’s 125 amino
acids long?
Amino Acid
p. 198
p. 198
Protein synthesis
transcription
translation
DNA
mRNA
tRNA
A
U
A
T
A
U
G
C
G
G
C
G
G
C
G
A
U
A
Review mutations…
what are the possible
effects to the
individual? Can
these mutations be
passed on to
offspring?
Tyr
Pro
p. 200
Mutations in Genes
p. 202
part of DNA template
mRNA transcribed from DNA
THREONINE
PROLINE
GLUTAMATE
GLUTAMATE
LYSINE
resulting amino acid sequence
base substitution in DNA
altered mRNA
THREONINE
PROLINE
VALINE
GLUTAMATE
LYSINE
altered amino acid sequence
deletion in DNA
altered mRNA
THREONINE
PROLINE
GLYCINE
ARGININE
altered amino acid sequence
What Happens to the
New Polypeptides?
• Where is the ribosome?
• Some function in the
cytoplasm
• Many enter the
endoplasmic reticulum
and move through the
endomembrane system
where they are modified
and shipped to their final
destination
Animal Metamorphosis
What has changed inside cells
to produce these changes in
body form. How is this
controlled? What is/are the
advantages of metamorphosis?
Cancer
• Tumors result when the normal mechanisms
controlling cell division malfunction.
• Benign or malignant
• Result from the accumulation of mutations
that transform the cell
• Mutagens and carcinogens increase the risk
of cancer
– Tumor suppressing genes
– Proto-oncogenes
• Viruses can insert genetic information into
host cells, and move genes to different
chromosomes
– Can we take advantage of this?
transcription
Pre mRNA
transcript
processing
Assembly of RNA on unwound regions of
DNA molecule
mRNA
rRNA
tRNA
protein
subunits
mature mRNA
transcripts
translation
At an intact
ribosome,
synthesis of a
polypeptide
chain at the
binding sites for
mRNA and tRNAs
ribosomal
subunits
mature
tRNA
Convergence
of RNAs
cytoplasmic
pools of
amino acids,
ribosomal
subunits and
tRNAs
final protein
For use in cell or for transport
p. 204