Download NUCLEIC ACIDS & PROTEIN SYNTHESIS Chapter 10

NUCLEIC ACIDS
&
PROTEIN SYNTHESIS
Chapter 10
Topics:
DNA
RNA
Protein Synthesis
CPI Biology
1
Understanding Heredity


Important discoveries:
 By 1940s, nucleic acid composition known; ribose &
deoxyribose sugars known
 Avery Oswald (1943) determined that DNA carried genetic
info
 Erwin Chargraff (1950) found that the amount of certain
nitrogen bases occurred in 1:1 ratio
 Linus Pauling (1948) found many proteins coiled into an helix (spiral, like a spring)
 Rosiland Franklin (late 1940s-early 50s) X-ray
crystallography on DNA, captured structure
 Maurice Wilkins (1950s, Kings College) colleague of
Franklin, worked on other aspects of DNA
 James Watson/Francis Crick (1950s) working on DNA
structure as well
The race was on….
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Structural Components
Nucleotide Structure consists of:
 Phosphate group
 Sugar – deoxyribose or ribose
 Nitrogen bases – adenine, guanine,
cytosine, thymine, uracil
 All nucleotides have same phosphate
group, 2 sugar possibilities, and
several base possibilities
3
Nitrogen Bases
 Purines – 2 rings of C & N atoms
 Adenine (A)
 Guanine (G)
 Pyrimidines – 1 ring of C & N atoms
 Thymine (T) (in DNA only)
 Cytosine (C)
 Uracil (U) (in RNA only)
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DNA Structure
 DNA components known, but how were
they “put together” & how did it work?
 Many scientists competed in the race to
determine what this molecule looked like.
Some worked to find the answer, others
worked to find the answer first.
 Rosiland Franklin
 Maurice Wilkins
 James Watson & James Crick
 Watson/Crick/Wilkins received Nobel Prize
(1963) for determining DNA structure
5
Double Helix of DNA
 DNA molecule:
 Double stranded – each strand composed of
alternating sugar & phosphate strands; 1 strand
going “up”, the other “down”
 “Ladder rungs” connecting the strands are 2
nitrogen bases; always a purine + a pyrimidine;
bonded by H Bond; pair combo same size
 Only possible base pair combos: AT, CG
 See pictures, next 2 slides
6
Nitrogen Base Pairs
 A-T
 Purine + Pyrimidine
 G-C
 Purine + Pyrimidine
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DNA Structure
Left Strand 3’ to 5’ UP
Right Strand 3’ to 5’ DOWN
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RNA Structure
 Single helix structure
 Single strand of alternating phosphate &
sugar (ribose) sugars
 Nitrogen base bonded to strand
 Bases: adenine & guanine (purines),
cytosine & uracil (pyrimidines)
 Uracil replaces thymine
 Sugar is ribose
 Ribose replaces deoxyribose
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Purine/Pyrimidine
Comparison
GCAT
Purines
Pyrimidines
2 Rings
1 Ring
3 H Bonds G
C
2 H bonds A
T (U)
DNA
GCAT
RNA
GCAU
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DNA/RNA
Comparison
DNA
RNA
Structure
Double Helix
Single Helix
Phosphate
Same
Same
Sugar
Deoxyribose
Ribose
Bases
Adenine
Thymine
Guanine
Cytosine
Adenine
Uracil
Guanine
Cytosine
Purine
Pyrimidine
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DNA Replication
 Replication – process of copying DNA
 DNA replication occurs during “S phase” of
Interphase
 Hydrogen bonds broken by helicases; DNA
double helix “unzips”
 DNA polymerases then move along single
(opened) strands & attach nucleotides to
“open” base; manufacturing a new strand
 H bonds join base pairs
 Covalent bonds join phosphate/sugar groups &
base to strand
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DNA Replication
-Helix unzips from bottom to top
-New nucleotide groups bond to
old strand
-Two new DNA double helixes form,
each having 1 old & 1 new strand
======================
-Mutations (change in nucleotide
sequence) can occur during
process; ~1/10,000 nucleotides
-Enzymes proofread/repair errors
in sequencing
-Other “agents” may cause
sequencing errors: chemicals, UV
radiation
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DNA Replication
 DNA replication important for mitosis
and meiosis
 Occurs during S phase of interphase
 Yields 2 identical DNA molecules
 For growth/repair of somatic cells
 Encodes the genetic information of
organism
 Enables genetic info to be passed to
subsequent generations
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Is that all DNA does?
 No, besides enabling genetic info to
be passed to subsequent generations
 DNA holds the code for all processes
that the organism is able to perform
 DNA codes for all the proteins that
the organism can make
 So how does DNA “make” these
proteins?
 Answer  RNA
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RNA Types
 Messenger RNA – mRNA
 Single uncoiled chain
 Transfer RNA – tRNA
 Single chain, folded into “cloverleaf”
shape
 Ribosomal RNA – rRNA
 RNA nucleotides in globular form, rRNA
+ proteins compose ribosomes
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mRNA
 Single, uncoiled chain
 Codon – set of 3 nucleotides
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tRNA
-Cloverleaf structure
-Anticodon sequence at
bottom, matches up to
codon sequence on mRNA
-Amino Acid attached to
3’end
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rRNA
-Ribosomes
composed of
nucleotides +
proteins in globular
form
-Ribosomes are site
of protein synthesis
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Transcription
 Process of copying information on DNA
to RNA & occurs in nucleus, 1st step in
protein synthesis
 Steps:
 1. Specific sections of DNA (genes) code for
specific proteins, the beginning of a gene is
marked by Promoters
 2. RNA polymerase (primary transcription
enzyme) recognizes the promoter and
binds to it, DNA begins to “unzip” at that
site
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Transcription steps, con’t.
 3. RNA polymerase attaches to DNA
nucleotide (promoter first) & begins adding
complementary RNA nucleotides that match
up
 4. RNA polymerase moves from 5’ to 3’
direction, adding nucleotides and
elongating the RNA strand
 5. RNA polymerase reaches the termination
signal, it breaks free from DNA strand
 6. DNA zips up, mRNA moves from nucleus
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Transcription
 Making of mRNA from DNA
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Translation
 Process of assembling
polypeptides (proteins) from info
encoded on mRNA; 2nd step in
protein synthesis
 Occurs at the ribosome in the
cytoplasm
 mRNA exits nucleus, joins to
ribosome (which is composed of rRNA
+ proteins)
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Translation steps
 1. mRNA to ribosome where it binds to
ribosome
 2. START codon is AUG
 Codes for methionine, signal to start
 3. Some codons code for nothing – this
signals process to start or stop
 4. Ribosome moves along the mRNA strand
to ‘read’ the codons
 5. tRNA contains an anticodon that codes
for an amino acid
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Translation, cont.
 6. tRNA finds & attaches to a specific amino
acid & brings it to the ribosome from
cytoplasm
 7. At the ribosome, matching mRNA codons
to the tRNA anticodons occurs
 8. As more tRNAs bring amino acids,
peptide bonds form between them
 9. As peptide bonds form, tRNAs drop
away, tRNAs go find more amino acids
 10. Ribosome continues to move along the
mRNA strand and the protein is built
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Translation, cont.
 11. When a STOP codon is encountered, the
process stops, the protein is complete
 12. Protein then collected for use in cell or
export from cell
 13. Protein undergoes refinement
(structure & function)
 remove AUG
 folding (3D structure)
 14. STOP codons are UAA, UAG, UGA
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Transcription: steps 1, 2
Translation: steps 3, 4
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CODONS in mRNA
-Codon-group of
3 bases, code for
An amino acid
-Note 3 STOP
Codons, UAA,
UAG, UGA
-Start codon is
AUG
-There are 64
codons
-Codons are
almost
universal for all
organisms
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Amino Acids
Phenylalanine
Proline
Glutamine Tryptophan
Leucine
Threonine
Asparagine Arginine
Isoleucine Alanine
Lysine
Serine
Valine
Tyrosine
Serine
Histidine
Aspartic
Acid
Cysteine
Glutamic
Acid
Glycine
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Overview
 Understand
DNA & RNA
 Understand
 Understand
 Understand
similarities/differences of
DNA replication
transcription
translation
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Quiz #1
 1. Name the components of DNA.
 2. What are the names of the bases
in DNA?
 3. Name the base pair possibilities in
DNA.
 4. What type of bond joins the base
pairs?
 5. What is the result of DNA
replication?
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Quiz Answers
 1. nucleotides
 Sugar + phosphate + base pairs
 2. thymine, adenine, guanine,
cytosine
 3. A-T, G-C
 4. hydrogen
 5. 2 identical DNA strands
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