Download DNA and Protein Synthesis

DNA: Molecule of Life
History
DNA
Structure
Protein
Synthesis
Gene
Regulation
History of DNA
H
I
S
T
O
R
Y
• By the 1940’s, scientists knew that
chromosomes consisted of both DNA and
protein but did not know which was the
genetic material.
• Scientists wanted it to be protein since they
knew more about its structure.
• The following experiments shed some light.
Heat-killed, diseasecausing bacteria
(smooth colonies)
Animation here
Disease-causing
bacteria (smooth
colonies)
Dies of pneumonia
Harmless bacteria Heat-killed, disease(rough colonies) causing bacteria
(smooth colonies)
Lives
Lives
Control
(no growth)
Live, disease-causing
bacteria (smooth colonies)
Harmless bacteria
(rough colonies)
Dies of pneumonia
Harmless, live R strain somehow became disease
causing S strain – transformation HOW?
Bacteriophage with
phosphorus-32 in
DNA
Phage infects
bacterium
Radioactivity inside bacterium
Bacteriophage with
sulfur-35 in protein
coat
Phage infects
bacterium
No radioactivity inside
bacterium
Hershey Chase Experiment
D
N
A
S
T
R
U
C
T
U
R
E
Nucleotide: the monomer
(repeating unit) of DNA
Phosphate
group
Nitrogen
bases
Deoxyribose
sugar
Nucleotide
Hydrogen
bonds-very
weak
Sugar-phosphate
backbone
Key
Adenine (A)
What limitations exist
in our model of DNA?
Thymine (T)
Cytosine (C)
Guanine (G)
DNA packing (ExpLIFE 12.1)
D
N
A
Nucleosome
Chromosome
DNA
double
helix
Coils
S
T
R
U
C
T
U
R
E
Supercoils
Histones
• Chromatin: DNA unassociated with structural
proteins.
• Chromosome is made up of a DNADNA Histone
protein complex.
• Compacts a very long (2m) sequence of DNA.
D
N
A
R
E
P
L
I
C
A
T
I
O
N
Helicase unwind and
separate the double
helix, breaking weak
H-bonds: replication
fork
DNA polymerases
rebuild each strand
adding nucleotides
to each side
according to basepairing rules.
DNA Replication Animation
Each new double
helix consists of
one old strand
linked to one new
DNA strand.
D
N
A
R
E
P
L
I
C
A
T • Errors sometimes occur (about 1 error/10,000 pairs)
I • If a mismatch occurs, the DNA polymerase can
backtrack, remove the incorrect nucleotide, and
O
replace it with the correct one.
N
Prokaryotic vs. Eukaryotic
What observations can
you make between the
Pro/Eukaryotic DNA?
• Eukaryotic chromosomes are so long that it would take 33
days to replicate a typical human chromosome if there were
only one origin of replication.
• Human chromosomes are replicated in about 100 sections that
are 100,000 nucleotides long, each section with its own
starting point.
• Because eukaryotic cells have multiple replication forks
working at the same time, an entire human chromosome
can be replicated in about 8 hours.
• What are the critical
characteristics of DNA that allow
both the lasting storage of
information and the transfer of
information through copying
(replication)?
• What are the dis/advanages of an
information transfer system that
uses as physical pattern, or
template?
How does the DNA store and
transmit these messages?
A particular sequence (a gene) along a
strand of DNA codes for the production
of a specific protein. In this activity, you
will explore the production of one
protein produced by your stomach. This
protein, pepsinogen, is an inactive form
of an enzyme that aids in digestion.
Exp Life CD: 11.4
Ribonucleic Acid (RNA)
Click to play the video.
DNA RNA
Double Strand
Single Strand
Deoxyribose
Ribose
Thymine
Uracil
Gene Transcription
Prokaryotesand
vs. Eukaryotes
Gene processing animation
Translation
RNA processing
Transcription: DNA RNA
DNA template
Non-template
RNA strand
TAC
ATG
AUG
AAG TTT
TTC AAA
UUC AAA
GAC
CTG
CUG
CAT
GTA
GUA
Click to play the video.
DNA
DNA unwinds
RNA
RNA polymerase copies at a rate of
60 nucleotides/sec
Translation observation (BSCS DVD 3 )
DNA
RNA
Translation details
RNA
polymerase
Nucleus
Phenylalanine
tRNA
Methionine
Ribosome
mRNA
Start codon
Lysine
mRNA
The Polypeptide “Assembly Line”
The ribosome joins the two amino acids—methionine and phenylalanine—and breaks the
bond between methionine and its tRNA. The tRNA exits, allowing the ribosome to bind to
another tRNA. The ribosome moves along the mRNA, binding new tRNA molecules and
amino acids.
Growing polypeptide chain
Ribosome
tRNA
Lysine
tRNA
mRNA
mRNA
Ribosome
Translation direction
Completing the Polypeptide
The process continues until the ribosome
reaches one of the three stop codons.
codons
The result is a growing polypeptide chain.
Codons in
mRNA
Start codon
Mutation - changes in DNA
1
DNA template
RNA transcript
Amino acids
•
•
•
•
2
3
4
5
TAC GCA TGG AAT ACT
ATG CGT ACC TTA TGA
AUG CGU ACC UUA UGA
Met– Arg– Thr– Leu stop
Substitution codon 2 as GTA
Substitution codon 2 as GCG
Insertion codon 1 TATC
Deletion nucleotide
Point Mutation
Silent Mutation
Frame Shift
Mutation
Normal hemoglobin GGG CTT CTT TTT
Sickled hemoglobin GGG CAT CTT TTT
Protein structure
As a result of this mutation, the proteins
are also misshapen causing sickled cells
to clog capillaries and prevent normal
flow of blood to body tissues, causing
severe pain.
• Transcribe and translate the two DNA sequences.
• What kind of mutation does this represent?
• Explain why the correct sequence is important to
protein synthesis.
• Assume the base sequence is GGG CTT CTT AAA
Would this result in sickled hemoglobin? Explain.
Chromosomal Mutations
(ExpLIFE 12.2)
Deletion
Duplication
Inversion
Translocation
How can the movement of genes take place?
Which mutation variety would be most damaging?
Regulation of Protein Synthesis
• Every cell in your body, with the exception of
gametes, or sex cells, contains a complete
copy of your DNA. Why, then, are some cells
nerve cells with dendrites and axons, while
others are red blood cells that have lost their
nuclei and are packed with hemoglobin? Why
are cells so different in structure and function?
If the characteristics of a cell depend upon the
proteins that are synthesized, what does this
tell you about protein synthesis?
Typical Gene Structure
• lac operon
(ExamView)
• Exploring a stretch of code of DNA
•Chromosome 11 Fly-over
Regulatory
sites
Promoter
(RNA polymerase binding site)
Start transcription
DNA strand
Stop transcription
Complexities of Gene Expression
• The relationship between genes and their effects is
complex. Despite the neatness of the genetic code,
every gene cannot be simply linked to a single
outcome.
• Some genes are expressed only at certain times or
under specific conditions.
• Variations and mistakes can occur at each of the steps
in replication and expression.
• The final outcome of gene expression is affected by
the environment of the cells, the presence of other
cells, and the timing of gene expression.
Section 12-5
1. Do you think that cells produce all the proteins
for which the DNA (genes) code? Why or why
not? How do the proteins made affect the type
and function of cells?
2. Consider what you now know about genes and
protein synthesis. What might be some ways
that a cell has control over the proteins it
produces?
3. What type(s) of organic compounds are most
likely the ones that help to regulate protein
synthesis? Justify your answer.