Download DNA - Cloudfront.net

DNA / Protein Synthesis
History of DNA Research
DNA – Deoxyribonucleic acid
1) Frederick Griffith (1928)- discovered that
a factor in heat-killed, disease-causing
bacteria can “transform” harmless bacteria
into ones that can cause disease.
– Griffith's Experiments
• Griffith set up four
individual experiments.
• Experiment 1: Mice were
injected with the diseasecausing strain of bacteria.
The mice developed
pneumonia and died.
• Experiment 2: Mice
were injected with
the harmless strain
of bacteria. These
mice didn’t get sick.
Harmless bacteria
(rough colonies)
Lives
• Experiment 3:
Griffith heated the
disease-causing
bacteria. He then
injected the heatkilled bacteria into
the mice. The mice
survived.
Heat-killed diseasecausing bacteria (smooth
colonies)
Lives
• Experiment 4: Griffith
mixed his heat-killed,
disease-causing bacteria
with live, harmless
bacteria and injected the
mixture into the mice.
The mice developed
pneumonia and died.
Heat-killed diseasecausing bacteria
(smooth colonies)
Harmless bacteria
(rough colonies)
Live diseasecausing bacteria
(smooth colonies)
Dies of pneumonia
• Griffith concluded that
the heat-killed bacteria
passed their diseasecausing ability to the
harmless strain.
Heat-killed diseasecausing bacteria
(smooth colonies)
Harmless bacteria
(rough colonies)
Live diseasecausing bacteria
(smooth colonies)
Dies of pneumonia
– Transformation
• Griffith called this process transformation because
one strain of bacteria (the harmless strain) had
changed permanently into another (the diseasecausing strain).
• Griffith hypothesized that a factor must contain
information that could change harmless bacteria into
disease-causing ones.
History of DNA Research
2) Oswald Avery (1944)- discovered DNA
was responsible for transformation
History of DNA Research
3) Hershey and Chase (1952)- their studies supported
Avery’s work by studying bacteriophage (a virus that
infects bacteria)
History of DNA Research
4) Watson and Crick (1953)- first
to develop a double-helix model
of DNA
DNA
• DNA is found
inside the nucleus
of every cell in your
body
DNA Structure
• DNA is made up of nucleotides.
Nitrogenous
Phosphate
Base
Sugar
Parts of a nucleotide
• A nucleotide contains three parts:
1) Phosphate group
2) 5-carbon sugar group (deoxyribose)
3) Nitrogenous bases (4 types)
•
•
•
•
Adenine (A)
Guanine (G)
Cytosine (C)
Thymine (T)
Purines (double rings)
Pyrimidines (single ring)
To help you remember:
CUT = PY
Chargaff’s Rule
• Erwin Chargaff (1949) discovered the basepairing rules for nitrogenous bases:
1) A always pairs with T
C always pairs with G
2) % A in DNA = % T in DNA
% C in DNA = % G in DNA
Cytosine
Guanine
Adenine Thymine
• Double Helix
– DNA molecule is composed of two long
chains of nucleotides twisted and held
together by hydrogen bonds in the center
between the nitrogen bases
• DNA Double Helix
• In even in your smallest chromosome
there are 30 million base pairs. How does
so much DNA fit in every tiny cell in your
body?
DNA
• You fold it!
• Think about how
much easier it is to
pack your suitcase
when everything is
nicely folded.
Can’t fit
Much more fits
when you
organize and
fold it.
• DNA must condense
(make itself smaller) by
folding itself around
proteins called
Histones.
• When DNA wraps
around Histones it
forms tight coils and is
called chromatin.
• What are histones?
– Histones are proteins that DNA wraps around.
• What is Chromatin?
– Chromatin is what you call DNA when it is
wrapped around the Histones.
Example:
Histone
DNA
Double Helix
Chromatin
DNA around
histones
Chromosomes
• When the
chromatin
forms coils and
condenses it
forms a
chromosome.
• See Fig. 12-10
in your book.
DNA
Double Helix
Chromosomes
Made up of
chromatin
Chromatin
DNA around
histones
Histone =
• DNA Double Helix  Chromatin  Chromosome
DNA Double Helix
DNA Chromatin
DNA Chromosome
http://www.biostudio.com/demo_freeman_dna_coil
ing.htm (dna coiling)
DNA Replication
• Occurs when cells divide.
(Cell division)
DNA Replication
• DNA makes an exact copy of itself
• takes place inside the nucleus during S
phase before cell division
Replication
• Each strand of the double helix
of DNA serves as a template
against which the new strand
is made.
DNA Base Pairing Rules
• A compliments T
• T compliments A
• G compliments C
• C compliments G
G
A
T
T
C
A
A
G
T
C
Replication
Step 1: The hydrogen bonds
between the double helix break
and two strands separate.
Each strand is called a
template strand.
Template
strand
Step 2: Two new
complementary strands are
formed following the rules of
base pairing. The new strands
are called complimentary
strands.
Compliment
strand
How DNA Replication
Works!
DNA polymerase is an enzyme that
adds the complimentary bases to the
DNA template strand and also
“proofreads” or checks that it is
correct.
DNA Polymerase
T
A
Semiconservative
Replication
•Template Strand
(original)
•CGTATCCGGAATTT
• The complimentary strand..
•GCATAGGCCTTAAA
Complimentary Template
strand
Strand
ACGGCAT
TGCCGTA
TACGGCAT
ATGCCGTA
Complimentary
• If I have a strand that DNA sequence of CAT what
would be on the complimentary strand?
• CAT
GTA
RNA
•
•
•
•
Ribonucleic acid
Single strand
made up of nucleotides
contains three parts:
– 1) Phosphate group
– 2) 5-carbon sugar group (ribose)
– 3) Nitrogenous bases (4 types)
• Adenine (A)
• Guanine (G) Purines (double rings)
• Cytosine (C)
• Uracil (U) Pyrimidines (single ring)
Base-pairing in RNA
1) A always pairs with U
2) C always pairs with G
Types of RNA
Type
Messenger RNA
(mRNA)
Ribosomal RNA (rRNA)
Transfer RNA (tRNA)
Function
Carries copies of
instructions to make
proteins
Is a part of ribosomes
Transfers each amino
acid to the ribosome to
help make proteins
Compare DNA and RNA
1)
Sugars are different:
Deoxyribose
H
H
OH
OH
Ribose
OH OH
OH OH
Compare DNA and RNA
DNA
RNA
2) A, G, C,T
(A–T, C-G)
A, G, C, U
(A-U, C-G)
3) Double stranded
Single stranded
4) only 1 type
3 types
Protein
• Proteins are made of building blocks
called amino acids.
• Proteins are different from one another by
the sequence, or order, of their amino
acids.
Protein
• There are 20 different amino acids.
• Thousands of proteins can be made from
these amino acids because there are
many different orders that they can be in.
•
Proteins are made in two steps:
1) Transcription
2) Translation
• What is transcription?
– The process where mRNA is made from a
DNA template
– Transcription happens in the nucleus
• What is translation?
– Translation is the decoding of an mRNA
message into a protein.
– Translation takes place on ribosomes in the
cytoplasm
Transcription
Translation
Transcription
• Protein synthesis begins when a strand of
(A) DNA unravels.
• The code for producing a protein is carried
in the sequence of the (B) bases in the
DNA.
• Each group of three bases forms a codon,
which represents a particular amino acid.
Transcription
• One of the unwound strands of DNA forms
a complementary strand called (C) mRNA.
• This process is called transcription.
• It takes place in the nucleus of the cells.
Bases
DNA
mRNA
Post-transcriptional modification
• DNA is composed of coding and
noncoding sequences
• Noncoding region = Introns
• Coding region = Exons (code for proteins)
• During transcription, introns are cleaved
and removed, while exons combine to
form useful mRNA
Post-transcriptional modification
E
I
E
I
E
initial DNA
 introns cleaved
pre-mRNA
 exons combine
final mRNA
Now look at the right side of the picture.
• The mRNA has moved into the cytoplasm,
where it attaches to a (D) ribosome.
• A phase of protein synthesis called
translation then begins.
Ribosome
mRNA
• A (E) tRNA approaches the ribosome.
• At one end of this molecule are three
bases known as an (F) anticodon.
• At the ribosome, each anticodon lines up
with its complementary codon on the
mRNA.
tRNA
Anticodon
Codon
Anticodon
• This occurs according to base pairing.
• At the other end of tRNA, an (G) amino
acid is attached.
• As the ribosome moves along the strand
of mRNA, new tRNAs are attached.
• This brings the amino acids close to each
other.
• The amino acids are
joined by peptide bonds,
and the resulting strand is
a protein.
Codon Chart
• To determine which amino acid we choose
we use this chart:
CODON
AGU
AGC
GGU
AMINO ACID
• What are mutations?
– Mutations are changes in the DNA
sequence that affects the genetic
information
Types of mutations:
•
•
Gene mutations result from changes in
a single gene
Chromosomal mutations involve
changes in whole chromosomes
–
Gene mutations:
•
Point mutations – affect only one nucleotide
because they occur at a single point
–
•
Include substitutions, additions, and deletions
Frameshift mutations – when a nucleotide is
added or deleted and bases are all shifted
over, leaving all new codons.
–
–
Include additions and deletions
Substitutions don’t usually cause a frameshift
Substitutions
DNA
mRNA
Amino acids
TAC GCA TGG AAT
AUG CGU ACC UUA
Met – Arg – Thr – Leu
Substitution TAC GTA TGG AAT
AUG CAU ACC UUA
Met – His – Thr - Leu
Original
One base change
Insertions
DNA
Original
mRNA
TAC GCA TGG AAT
AUG CGU ACC UUA
Insertion TAT CGT ATG GAA T AUA GCA UAC CUU A
Many base changes
Amino acids
Met – Arg – Thr – Leu
Ile – Ala – Tyr - Leu
Deletions
• Chromosomal mutations:
– Include deletions, duplications, inversions,
and translocations.
• Deletions involve the loss of all or part
of a chromosome.
• Duplications produce extra copies of
parts of a chromosome.
• Inversions reverse the direction of
parts of chromosomes.
• Translocations occurs when part of one
chromosome breaks off and attaches to
another.
• Significance of Mutations
• Many mutations have little or no effect on gene
expression.
• Some mutations are the cause of genetic
disorders.