Download DNA RNA PS PPT

Chapter 12 and 13
DNA, RNA and
Protein Synthesis
PowerPoint Lectures for
Biology: Concepts and Connections, Fifth Edition
– Campbell, Reece, Taylor, and Simon
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Discovery of the Role of DNA
A. 1928 - Frederick Griffith discovers
transformation in bacteria :
* discovered that “something” was able to transform
harmless (non – virulent) bacteria into harmful (virulent)
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Discovery of the Role of DNA (cont’d)
B. 1944 -Oswald Avery
and colleagues show
that DNA can
transform bacteria
C. 1952 - Alfred Hershey and
Martha Chase use bacteriophage
to confirm that DNA is the
genetic material
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Hershey-Chase Experiment: Infected cells make
more virus by injecting their DNA
animation
1
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Discovery of the Role of DNA (cont’d)
D. 1953 - James Watson and Francis Crick propose a
structural model for the DNA molecule
Based On:
1. X-Ray crystallography images
prepared by Maurice Wilkins
and Rosalind Franklin
2. Chargraff’s Rule:
# of Adenines = # of Thymines
# Guanines = # of Cytosines
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
DNA and RNA are Polymers of Nucleotides
• Both are nucleic acids made of long chains of nucleotide
monomers
• A nucleotide (building block of a nucleic acid)
has 3 parts:
1.
A phosphate (PO4-)
group that is
negatively charged
2. A 5-Carbon sugar
(deoxyribose in DNA
or ribose in RNA)
3. A nitrogencontaining base
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
DNA (deoxyribonucleic acid) bases:
Thymine (T)
Cytosine (C) Adenine (A) Guanine (G)
pyrimidines
Pyrimidines: single ring bases
Purines: double ring bases
Complimentary binding pattern:
• Adenine + Thymine
(share 2 hydrogen bonds)
• Cytosine + Guanine
(share 3 hydrogen bonds)
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
purines
RNA: ribonucleic acid
Similar to DNA except:
• Sugar in RNA = ribose
• Base “uracil” instead of thymine
• Single stranded
Figure 10.2C, D
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
The Structure of DNA
• Two polynucleotide strands wrapped around each other in a
double helix
• A sugar-phosphate backbone
• Steps made of hydrogen-bound bases (A=T, C = G)
Twist
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
DNA REPLICATION:
Starts with the separation
of
DNA strands
• Enzymes use each strand as a
template to assemble new
nucleotides into complementary
strands…“semi-conservative”
(Meselson & Stahl 1958)
• Portions to be replicated must
untwist first
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
DNA replication begins at specific sites on double helix
1.
DNA segments unwind
2. Helicase splits H bonds between bases,
unzip DNA
3. Binding proteins keep unzipped DNA
apart (Single Stranded Binding
Proteins)
4. Primase makes a short RNA primer
because DNA polymerase can only
extend a nucleotide chain, not start
one.
replication
forks
5. DNA polymerase adds new nucleotides
to the 3’ end of daughter strand that
are complimentary to the parent
strand
6. RNase H cuts out original primers
7. DNA polymerase fills in gap of removed
primers
Animation/tutorial
9. Two identical double helices
8. DNA ligase glues S/P backbone where
needed
•Topoisomerase: prevents further coiling at replication fork
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
A Structural Problem with DNA Replication
•
Each strand of the double helix is
oriented in the opposite direction
(“anti-parallel”)
•
“prime” #’s refer to carbons in the
sugar
•
At one end, the 3’ carbon has an (OH)
and at the opposite, a 5’ carbon has
the PO4-
•
Why does this matter?
DNA polymerase can only add
nucleotides to the 3’ end. A daughter
strand can only grow from 5’  3’
•
Therefore, only one daughter strand
is made continuously (leading strand)
•
The other strand (lagging strand) is
made in a series of short pieces
(Okazaki fragments), later connected
by DNA ligase
Animation/tutorial
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
animation
When DNA can repair mistakes and when it can’t
DNA Repair enzymes work like a spell checker
•
Cut out wrong sequences
•
Undamaged strand is template
•
Only 2 or 3 stable changes per year
: some severe, others are not
• Mutations Inheritable changes occur in gametogenesis
•
•
Now the “wrong” sequences are copied
–
Ex: cystic fibrosis (CF): a deletion of 3 nucleotides in a certain gene
–
Ex: sickle cell anemia: one nucleotide substitution in the hemoglobin
gene
Mutagen: a mutation causing substance (can break DNA)
–
Ex: X-Rays, radioactivity, nicotine
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Protein Synthesis: the transfer of information from:
DNA  RNA  Proteins “gene expression”:
A gene is a linear sequence of many nucleotides. 3 Types:
1. Structural genes: have info to make proteins
2. Regulatory genes: are on/off switches for genes
3. Genes that code for tRNA, rRNA, histones
DNA
• double stranded
• A T C G
• deoxyribose sugar
vs.
•
•
•
•
RNA
single stranded
A U C G
ribose sugar
3 types of RNA:
•messenger, transfer, ribosomal
mRNA (messenger): copies DNA’s message in nucleus  brings it to cytoplasm
tRNA (transfer): carries amino acids to mRNA so protein can be made
rRNA (ribosomal): major part of the ribosome. Helps link amino acids from
tRNA’s together  assemble protein
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Protein Synthesis is Two Steps:
1. Transcription:
The DNA of the
gene is
transcribed into
mRNA
2. Translation:
decoding the
mRNA and
assembling the
protein
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Transcription: Eukaryote
• DNA sequence (message for protein)
is transcribed by mRNA
• Only one strand (non-coding strand)
is needed as a template
• Steps:
1.
2.
3.
4.
5.
6.
RNA polymerase splits H bonds in DNA
section
RNA polymerase travels along non-coding
strand of DNA. RNA nucleotides join in a
complimentary pattern (A=U, C=G)
A termination signal is reached,
transcription is over
mRNA strip detaches from DNA, DNA
helix closes up
mRNA is processed: Introns are cut out,
Exons are glued together, cap and tail are
added.
Mature mRNA leaves nucleus through
pores  cytoplasm for next step
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Translation: the synthesis of proteins using
mRNA, tRNA and ribosomes
• The Genetic Code: the language in which instructions for
proteins are written in the base sequences
• Each triplet of mRNA bases is a “codon” because it will
“code” for 1 amino acid
– Ex: AUG GUC CCU AAU CCU
Met – Val – Pro – Asn – Pro
– Original coding strand of DNA (the actual gene):
ATG GTC CCT AAT CCT
• Only difference: U is substituted for T
– Use the Genetic Code chart to “decode” mRNA message
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
The Genetic Code is the Rosetta Stone of Life
–
–Nearly all organisms use
exactly the same genetic code
– More than one codon for most
amino acids = degenerate
nature…a change (mutation) in
gene does not always mean a
different amino acid.
– what does CAU code for?
ACU? UAU? GCC?
– how many codons for Leu?
– what is special about AUG and
it’s amino acid, Methionine?
– what is special about UAA,
UAG, and UGA?
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
An exercise in translating the genetic code:
Step 1: fill in
corresponding DNA
bases to dark blue
strand (non-coding)
Step 2: Transcribe
the dark blue
strand into mRNA
(pink)
A
T
G
A
Coding strand
(gene)
Step 3: Translate
the codons into
correct amino acids
(use chart)
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
A
G
T
T
T
T
transcription
translation
A
G
An exercise in translating the genetic code: answers
Step 1: fill in
corresponding DNA
bases to dark blue
strand (non-coding)
Step 2: Transcribe
the dark blue
strand into mRNA
(pink)
Step 3: Translate
the codons into
correct amino acids
(use chart)
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
How Does Translation Happen?
Need: tRNAs and ribosomes (rRNA)
tRNA: single stranded RNA, folded up
– 2 parts: anticodon and aa attachment site
Ribosome: 2 protein subunits and
ribosomal RNA
•
allows aa’s to attach by making peptide
•
•
bonds
travels along mRNA strip, tRNA’s join and
bring correct amino acids
3 sites on ribosome:
• A site – where new tRNA’s and amino acids join
• P site – where protein is growing
• E site – where empty tRNA’s exit ribosome
Translocation: as ribosome moves, tRNA’s move from
A site to P site. “A” site is now open for new
tRNA with attached amino acid to join
animation
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Put It All Together:
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Mutations can change the message of genes
Mutations:
• changes in DNA
base sequence
• caused by errors
in DNA replication,
recombination, or
by mutagens
• substituting, inserting,
or deleting nucleotides
also alters a gene
“point mutation”…may or may
not alter amino acid sequence
“frame-shift mutation”…most
devastating to protein structure
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
MUTANTS –
• Mutant Animals!
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings