Download DNA Structure and Function

Bsdiejssaiwkdmfkroepeldldkfjffjgjjgkiolpogmvnrikdkdldleleeot
I bet that you can read this information but not the one above.
-.. -.-- --- ..- .-. …. --- -- . .-- --- .-. -.-
The requirements for an information
system or a code:
There must be at least 2 signals
The order of the signals is important
The grouping of the signals is important
DNA Structure and Function
Nucleotide:
Sugar
Phosphate
Nitrogen Base
Nitrogen Bases:
Purines: Adenine and
Guanine
Pyrimidines: Cytosine and
Thymine
Functions of DNA
• Information to make proteins
• Copy itself (must pass information on to
new cells
Structure Function Relationships
Base Pairs:
Why do Purines only bond with Pyrimidines?
Why does only A pair with T and G pair with C
Bonding:
Why is the backbone bonded together with covalent bonds?
Why are the base pairs hydrogen bonded
Determination of DNA Structure
• Rosalind Franklin develops new x-ray
crystallography technique to get a clear picture
of DNA
• In 1953 Watson and Crick
published the structure of DNA
using Franklin’s
data without
her knowledge
What the X-ray Crystallography
Looked Like
DNA is obviously the information molecule – It
plays both a genetic role and a hereditary role
•
•
•
•
=
How much information is there in the DNA of a cell?
6 x 109 base pairs per cell
0.34 nm (10-9m) between base pairs
The length of DNA/cell
2m
There is a lot of DNA in one cell!
• Amount of DNA in 1 cell is equal to 30 complete sets of Encylopedia
Brittanica
• If the nucleus was the size of a tennis ball, there would be 4 miles of
DNA in it.
• How do you fit 2 m of DNA in a 1x10-5 nucleus?
Compaction Ratio
– 20m thread/.02m capsule =
– 1000 x compacted
– 2m DNA/1x10-5 m nucleus =
– 200,000 x compact
????????
DNA is arranged into chromatin – wrapped around proteins to pack
it in
Chromatin
• Chromatin – 2 m of DNA must fit in a 1x10-5 m
nucleus. DNA wrapped around proteins to
organize it and allow it fit into the nucleus
• Remember – it is condensed 200,000 x to fit in
the nucleus
• It is still loosely coiled enough that enzymes can
get into the DNA to copy it and make mRNA for
protein synthesis
• It is the normal form of DNA during all phases of
the cell cycle except mitosis
Chromatin
Chromosomes
• DNA compacted 12,000 times from
chromatin
• Cannot read or copy the DNA in
chromosomes – it is too tightly wound
• Formed solely during mitosis in order to
divide the doubled DNA in ½
• Protects the DNA when the nucleus
breaks down in mitosis
A Real Chromosome
DNA released
from a
chromosome
What is the relationship between DNA,
genes, chromosomes, and the genome?
• A gene is a segment of DNA that codes for a protein
• There are thousands of genes on each chromosome
– which is a folded up piece of chromatin
• All of the genes on all of the chromosomes is the
genome
Makes a few
proteins to get
ready for
mitosis
The Cell Cycle
2 new cells form
Growth 2
Growth 1
Hours to days
Making
proteins
Normal cell
functions
Makes an exact
copy of DNA
3-6 hours
G0
DNA Replication is SemiConservative
A
-
T
A - T
A -
T
G
-
C
G - C
G -
C
G
-
C
G - C
G -
C
C
-
G
C - G
C -
G
A
-
T
A - T
A -
T
T
-
A
T - A
T -
A
T
-
A
T - A
T -
A
C
-
G
C - G
C -
G
Replication Problems to Overcome
• If you open all 2 m of DNA it will
randomly base pair and tangle up
• How do you copy 6x109 base pairs in 36 hours
Steps of Replication
• Enzymes open the DNA at Origins of
Replication (there are many on each piece of DNA)
– Each origin makes 2 replication forks
• Helicase begins to unzip DNA
• Many DNA polymerase enzymes add
the complementary nucleotides (they form
covalent bonds between the sugar of 1 nucleotide and the phosphate
of another)
• DNA proof-reading enzymes check for
mistakes (this happens as base pairs
are added)
DNA Mutations – change in 1 or more nucleotide
nitrogen bases in the DNA
• Errors in replication – DNA polymerase
makes an error about 1000 base pairs
• DNA proofreading enzymes attached to
the polymerase correct the mistakes
• There are usually about 3-6 permanent
mistakes/replication
How can mutations occur
• A mistake in replication not picked up by
the proofreading enzyme
• Environmental insults
Radiation (UV, X-rays, radioactive
molecules)
Toxic chemicals in air, food, cigarette
smoke
How can mutations affect cells
and organisms?
• It may not change anything in the cell at all
• If nucleotides change, repair enzymes
may fix them
• If nucleotides are changed and repair
enzymes don’t fix them, the cell should
undergo apoptosis (cell suicide) before it
enters S phase.
How can mutations affect cells and
organisms?
• If the change isn’t picked up by repair
enzymes and the cell doesn’t undergo
apoptosis:
– It can make a cell make a mishappen protein
– That protein can be a little or a lot mishappen
– Depending on how mishappen and how important
that protein is to the cell will determine if the cell
malfunctions or not
– If it malfunctions – the cell may die or it could become
cancerous
How can mutations affect cells
and organisms?
• Unless it becomes cancerous – the
malfunctioning cell will not change or
affect the organism as a whole!
• In order for a mutation to have an effect
on the organism as a whole – it must
occur in the sperm, egg, or embryo –
then every cell of the offspring’s body will
have the mutation so it will actually change
the trait of the organism.
Effects of DNA Mutations on
Organisms (if in sperm or egg)
• No effect
Change is not in a gene
Still codes for same aa
aa change doesn’t change protein folding
• Negative Effect
Significantly changes protein shape so that a
function cannot be performed or some body
part is misshapen etc.
• Positive Effect
The change in the protein shape gives the
organism a survival advantage