Download week7_DNA

DNA Structure and
Function
(Not on mid2)
Nucleic Acids (polymer)
• Monomer = nucleotides, the
building blocks of nucleic acids
• Structure = three parts: sugar,
phosphate, and nitrogencontaining base
Sugar-Phosphate Backbone
• Nucleotides
connected together
with a covalent
bond.
• Alternating sugars
and phosphates
Nucleic Acids
• DNA: Four bases:
o
o
o
o
Adenine (A)
Guanine (G)
Thymine (T)
Cytosine (C)
• Sugar is deoxyribose
• Double stranded
• RNA: Four bases:
o
o
o
o
Adenine (A)
Guanine (G)
Uracil (U, replaces T)
Cytosine (C)
• Sugar is ribose
• Single stranded
Nitrogenous Bases
• DNA -Four bases:
o
o
o
o
Adenine (A) ad-den ēn
Guanine (G)
Thymine (T)
Cytosine (C)
• Memory trick,
o pyrimidines have a
“y” in the name
Base Pairing
• DNA is 2 strands
(molecules) held
together by H-bonds
• Bases form hydrogen
bonds with each other
– A pairs with T (& vc vs)
– C pairs with G (& vc vs)
DNA
Where are
the H-bonds?
DNA Structure
• The bonds between
which 2 bases are
stronger G&C or A&T?
• H-bonds are very
week, break & reform
• W/ thousands of bases
& thousands of bonds,
DNA is held together
DNA
• DNA is a polar molecule
• It also has a negative charge
• Dissolves well in water
Determining that DNA is the
Genetic Material
• Everyone knows …DNA…genetic material
• This was not always known
• Early studies .. microscopes.. genetic
material was in the chromosomes
– Made of both protein & DNA
– Most biologist .. 1940 .. protein as .. more
complex.
• Review experiments … DNA .. the genetic
material
Griffith’s Experiment
• 1928
• Two strains of bacteria
– R – harmless (1)
– S – deadly (2)
• Heat killed Strain S is
also harmless (3)
• Something from heat
killed Strain S makes
Strain R deadly (4)
Avery, MacLeod, and McCarty
•
•
•
•
•
1944
Isolated compounds from Strain S
Added these to Strain R
DNA transformed Strain R into Strain S
“Proved” DNA was the genetic material
Determining that DNA is the
Genetic Material
Head
DNA
Tail
Tail fiber
300,000
• HERSHEY –
CHASE: 1952
• Determined that
the heredity
material was DNA
& not protein
• Studied the
bacteria virus T2
Determining that DNA is the Genetic
Material
Phage
Bacterium
Radioactive
protein
DNA
Batch 1
Radioactive
protein
Mix radioactively
labeled phages with
bacteria. The phages
infect the bacterial cells.
Batch 2
Radioactive
DNA
Empty
protein shell
Phage
DNA
Radioactivity
in liquid
Centrifuge
Agitate in a blender to
separate phages outside
the bacteria from the
cells and their contents.
Pellet
Centrifuge the mixture
Measure the
so bacteria form a
radioactivity in
pellet at the bottom of
the pellet and
the test tube.
the liquid.
Radioactive
DNA
Centrifuge
Pellet
Radioactivity
in pellet
Determining that DNA is the
Genetic Material
• DNA in pellet, protein in the supernatant
• The pellet contained the viral genetic
material not the liquid supernatant
• “Proving” DNA is the genetic material
The Structure of DNA
• FRANKLIN and
WILKINS: 1950’s
• X-ray crystalography
determined that DNA
is a double helix
The Structure of DNA
• WATSON and
CRICK: 1953
• Determined that DNA
was a double helix
• Made a DNA model
Determining the Structure of
DNA
•
•
•
•
Watson & Crick later won the nobel prize
Rosalind Franklin died of cancer young
Brief video of photo 51
For more info see:
http://www.pbs.org/wgbh/nova/photo51/
DNA Structure in more detail
Two strands run in
opposite directions
Nucleotide Functions
Nucleotides Play Diverse Roles in
Organisms:
1. Used as “energy currency” in cells (ATP)
2. Are chemical messengers of cells, (cAMP)
3. Nucleotide coenzymes transport electrons
and hydrogen atoms (examples: NADH and
FADH2)
4. Nucleotides also serve as building blocks for
nucleic acids
Nucleic Acid Functions
1. DNA stores genetic information (traits and
inheritance)
2. RNA translates this genetic info into
protein
Organization of DNA
• Eukaryotes
– Billions of base pairs –
several linear
chromosomes
– Genes not grouped
– Mostly non-coding
DNA
– Nucleus?
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DNA in the cell
• Humans have 3 billion
nucleotide base pairs
• Roughly 6 feet of
DNA in the nucleus of
each cell
• How does it all fit?
DNA Packaging
• Eukaryotic chromosomes are very large
• Must be packaged
– Unavailable for transcription
• Unpacking must occur before transcription
Levels of DNA
Packaging
• Fully condensed,
seen at metaphase
• Tightly packed loops
• 30 nm fibers
• Histone spool
• Double helix
Gene Expression
• Every cell in your body came
from 1 original egg and sperm
• Every cell has the same DNA
and the same genes
• Except the gametes which
have half the DNA/genes
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Gene Expression
• Every cell has the same DNA, yet,
each cell is different, specialized
• How can they differ?
• Due to gene expression
– Which genes are turned on/off
– How much product they make
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Gene Expression
• DNA must be copied
faithfully when cells
divide so that DNA is
the same in all cells
• Will have a lesson on
gene expression
Chromosome Animation Review of
of DNA Packaging
• http://www.biostudio.com/demo_freeman_
dna_coiling.htm
• (Works in Internet Explorer, may not in FireFox)
Organization of DNA
• Prokaryotes
– Several million base pairs one circular piece
– Related genes grouped
together
– Mostly coding DNA
– Nucleus?
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