Download DNA, RNA and Protein

DNA, RNA and Protein
How the Information in DNA
Is Used to Build a Protein
Information Flow From DNA
replication
(before cell
duplicates)
Gene: sequence
of DNA that codes
for a protein
DNA
transcription
(ongoing parts of
cell metabolism)
RNA
translation
Protein
DNA and RNA Structure
Primary
Structure
Secondary
Structure
DNA
RNA
Chain of
nucleotides
Double
helix
Chain of
nucleotides
Single
folded chain
Nucleotide =
phosphate + sugar + nitrogen-containing base
DNA and RNA Structure
DNA
Purine
bases
Pyrimidine
bases
5-carbon sugar
Adenine (A)
Guanine (G)
Adenine (A)
Guanine (G)
Cytosine (C)
Thymine (T)
Cytosine (C)
Uracil
(U)
deoxyribose
ribose
OH
Phosphate
RNA
H
PO4
OH
PO4
OH
Nucleotide Chain
Nucleotides are joined
together by dehydration
synthesis
The phosphate of one
nucleotide is joined to
sugar of next
nucleotide, forming a
“sugar-phosphate
backbone”
3’ end
A
C
G pairs with C
T
A
A
T
G
C
A
T
3’ end
has free sugar
G
5’ end
has free phosphate
•Two nucleotide
chains
•In opposite
orientations
•Held together
by hydrogen
bonds
•Twisted into a
helix
T
DNA Structure
A pairs with T
5’ end
Applying Your Knowledge
In the DNA double helix, which base
is paired with adenine?
1. Adenine
2. Cytosine
3. Guanine
4. Thymine
5. Uracil
DNA Replication
•DNA chains separate
•Each chain is used
as a pattern to
produce a new chain
•Each new DNA helix
contains one “old”
and one “new” chain
DNA Replication
DNA replication requires
1. Enzymes, including DNA polymerase
that adds nucleotides in a 5’3’ direction.
2. nucleotides
3. energy
5’—A G C T — 3’
3’— T C G A — 5’
5’— A G C T— 3’
3’—T C G A — 5’
Enzymes Involved
in DNA Replication
4
Enzyme
Function
Helicase
Unwinds Double Helix
Primase
Produces RNA primer as starter
for DNA strand
Synthesizes DNA in a
5’  3’ direction from a primer
DNA Polymerase
Exonuclease
Removes RNA primers
DNA ligase
Seals gaps in sugar-phosphate
backbone
Directionality of DNA Replication
Continuous
Synthesis
Discontinuous
Synthesis
On the 3’ 5’ template
On the 5’ 3’ template
Forms small Okasaki fragments that
are joined by DNA ligase
Applying Your Knowledge
1.
2.
3.
4.
Two new chains
Two old chains
One old and one new chain
One helix has two new chains
and one has two old chains
5. None of these is correct.
After DNA replication, what is the composition
of the new double-helical molecules?
5’
Building Your
DNA Model
3’
Join the
phosphate of
one nucleotide
to the sugar of
the next one
One chain can
have bases in
any order, the
other chain
must be
complementary
3’
5’
Your completed model will have
two DNA chains, each with 9
nucleotides.
Transcription = Production of RNA Using
DNA as a Template
•DNA chains separate
•ONE DNA chain is used
as a pattern to produce
an RNA chain
•RNA chain is released
and the DNA chains
reform the double-helix
In DNA In RNA
A
U
T
A
G
C
C
G
Transcription
5
Transcription requires
1. Enzymes, including RNA polymerase
that adds nucleotides in a 5’3’ direction.
2. nucleotides
3. energy
3’---TACAAAGAGACT---5’
5’---ATG TTTCTC TGA---3’
3’---TACAAA GAGACT---5’ DNA template
5’---AUGUUUCUCUGA---3’ mRNA
5’---ATG TTTCTC TGA---3’
Applying Your Knowledge
What is the sequence of an RNA molecule
transcribed from a DNA template strand
that reads 3’-ATG-5’?
1. 5’-TAC-3’
2. 5’-CAU-3’
3. 5’-AUG-3’
4. 5’-UAC-3’
5. 3’-TAC-5’
Products of Transcription
• Messenger RNA
Contains the code words for
the sequence of amino
acids in a specific protein
CODON = group of three
nucleotides acting as a
code word for an amino acid
Interrupted Genes
Eukaryotic Genes have interruptions
within regions coding for protein
intron = interrupting sequence
exon = portion of coding region
Exon 1
intron 1
Exon 2
intron 2
Exon 3
mRNA Processing
DNA
Exon 1
Exon 2
intron 1
Exon 3
intron 2
In nucleus
Transcription
Primary transcript RNA
5’
Exon 1
Exon 2
intron 1
intron 2
Exon 3
3’
Add 5’ cap
G
Exon 1
Exon 2
intron 1
Exon 3
intron 2
Add 3’ poly-A tail
G
Exon 1
intron 1
X
X
Exon 2
X
intron 2
X
Exon 3
AAAAAAAA……
Remove Introns
Splice Exons
together
G
Exon 1
Exon 2
Exon 3
AAAAAAAA……
Mature mRNA leaves for cytoplasm
Products of Transcription
• Transfer RNA
“Translates” the message by
bringing a specific amino acid into
the correct position on the growing
protein chain
Has ANTICODON = a group of
three nucleotides on a tRNA that
recognizes a mRNA codon
Has amino acid attachment site
mRNA
In mRNA In tRNA
A
U
U
A
G
C
C
G
Genetic
Code
Chart is written as a CODON dictionary, reading 5’3’
Products of Transcription
• Ribosomal RNA
One of the structural
components of the
ribosome
Ribosome = organelle
where protein
synthesis occurs
Has sites to bind both
mRNA and tRNA
for tRNA
for tRNA
small ribosomal
subunit
mRNA binding site
Applying Your Knowledge
Which molecule contains the information
for assembling the amino acids in the
correct order in the protein?
1. rRNA
2. tRNA
3. mRNA
4. All of these
5. None of these
3’
Your completed messenger RNA
will have 9 nucleotides.
5’
Read the
template from
3’5’ to
produce the
mRNA from
5’3’
5’
Building Your
DNA Model
3’
Choose one
DNA chain as
the template
for RNA
Translation
6
At the ribosome, codons in mRNA are
recognized by tRNA anticodons to place
amino acids in the specific sequence specified
by the DNA.
Three Stages of Translation:
Initiation- assemble components to start process
Elongation- add amino acids in repeated cycles
Termination- release protein product
Translation
Initiation
mRNA binds to ribosome
First tRNA binds to mRNA
met
UAC
5’---AUGUUUCUCUGA---3’ mRNA
Translation
Elongation
Next tRNA binds to mRNA
met phe
UACAAA
5’---AUGUUUCUCUGA---3’ mRNA
Translation
Elongation
Amino acids are joined
First tRNA is released
UAC
met phe
AAA
5’---AUGUUUCUCUGA---3’ mRNA
Translation
Elongation
Ribosome moves by one codon
UAC
met phe
AAA
5’---AUGUUUCUCUGA---3’ mRNA
Translation
Elongation (second cycle)
Next tRNA binds to mRNA
UAC
met phe leu
AAA GAG
5’---AUGUUUCUCUGA---3’ mRNA
Translation
Elongation (second cycle)
Amino acids are joined
Second tRNA is released
UAC
met phe leu
GAG
5’---AUGUUUCUCUGA---3’ mRNA
AAA
Translation
Elongation (second cycle)
Ribosome moves by one codon
UAC
met phe leu
GAG
5’---AUGUUUCUCUGA---3’ mRNA
AAA
Translation
Termination
Termination factor binds to stop
codon
UAC
met phe leu
T
GAG
5’---AUGUUUCUCUGA---3’ mRNA
AAA
Translation
Termination
Protein chain is released
Other components separate
met phe leu
UAC
T
GAG
AAA
5’---AUGUUUCUCUGA---3’ mRNA
Applying Your Knowledge
If the mRNA sequence for codons 5, 6, and 7 of
a protein is 5’-AAG-AUU-GGA-3’, what is
the amino acid sequence in the protein?
1. Gly-ile-lys
2. Arg-leu-glu
3. Glu-leu-arg
4. Asn-met-gly
5. Lys-ile-gly
CODON
Attach 3 bases
to the tRNA to
form the
anticodon
Building Your
DNA Model
Serine
Read the CODON
from 5’3’ to
find the name of
the amino acid
Your completed model will have 3 tRNAs, one
for each codon in mRNA. Show the name of the
amino acid carried by each tRNA.
Summary of Completed DNA Model
• One DNA double helix, two chains of 9
nucleotides each
– one chain can have any sequence
– second chain must be complementary
• One chain of mRNA, 9 nucleotides long
– must be complementary to one of the two
DNA chains (DNA template is 3’5’,
mRNA is 5’3’)
• Three tRNAs with appropriate amino
acids attached
– tRNA anticodons must match mRNA codons