DNA Structure and Function

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DNA Structure and Function

• Homework 1 is posted and due 9/20
• Bonus 1 is posted and due 10/25

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How is information transferred between cells?
Fig 7.2
Different strains of bacteria are injected into
mice.
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How is information transferred between cells?
Fig 7.2
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How is information transferred between cells?
Fig 7.2
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How is information transferred between cells?
Fig 7.2
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Fig 7.2
What has happened to the bacteria?
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• DNA is the transforming agent

Fig 7.3
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The Structure of DNA
If these two can win a Nobel prize
James Watson and Francis Crick
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Data showing uniformity of DNA structure.
Rosalind Franklin
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Fig 7.58.2
Nucleotides have a sugar backbone
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Fig 7.5 8.2
This subtle difference in structure has profound
effects.
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Fig 7.58.2
Plus four different bases
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Together with a phosphate nucleotide
Fig 7.5
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Fig 7.5
Together with a phosphate nucleotide
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Fig 7.8
Connect nucleotides by covalent bond strand
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Fig 7.8
DNA is typically double stranded The strands
are connected by hydrogen bonds
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Data showing uniformity of DNA structure.
Rosalind Franklin
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Figure 7-10
Fig 7.8

• Base pairing in DNA

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Figure 7-9
Fig 7.9

• Two representations of the DNA double helix

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Fig 8.11
DNA stores information, but does not do anything.
The information must be expressed to be useful.
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The relationship between DNA and genes
a gene
promoter
coding region
terminator
non-gene DNA
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DNA Composition

• In humans
• Each cell contains 6 billion base pairs of DNA.
• This DNA is 2 meters long and 2 nm wide.
• 97 does not directly code for amino acids
• In a single human cell only about 3-5 of genes
  are expressed at a time.

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Length of human DNA in each cell
Width of DNA
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DNA Composition

• In humans
• Each cell contains 6 billion base pairs of DNA.
• This DNA is 2 meters long and 2 nm wide.
• 3 directly codes for amino acids
• 10 is genes
• In a single human cell only about 5-10 of genes
  are expressed at a time.

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The relationship between DNA and genes
a gene - DNA used to produce RNA or protein
promoter
coding region
terminator
non-gene DNA
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Five Perspectives of a Gene
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Genes act as units of hereditystoring and
passing on information.
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Genes act as units of heredity storing and
passing on information.
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Genes are seen as a cause of disease
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Genes are seen as a cause of disease
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Sickle-cell anemia is caused by a single
nucleotide change in the hemoglobin gene
Fig 6.5
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Fig 8.11
Genes code for proteins
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Genes code for proteins

• Proteins are the doers of the cell.
• They act as
• Enzymes
• Structural Support
• Transporters
• Signals

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Genes act as switches, controlling development
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Genes act as switches, controlling development
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Genes are replicators (selfish gene)
From Biology 7th ed. by Campbell et alfig 19.14
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Fig 5.25
Viruses infect living cells, take over, and
produce more virus.
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Bodies are vessels for the transmission of genes
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• Five Perspectives of Genes
• Genes act as units of heredity
• Genes are seen as a cause of disease
• Genes code for proteins
• Genes act as switches, controlling development
• Genes are replicators (selfish gene)

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Transposons
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Genes are replicators (selfish gene) Transposons
mobile DNA
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Barbara McClintock, discoverer of transposons
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Transposons are self-moving DNA
Fig 14.8
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Fig 14.8
Transposons move within genomes via the action of
transposase
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Fig 14.4
transposase
transposon
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Fig 14.4
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Fig 14.4
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Fig 14.4
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Fig 14.4
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Genes are replicators (selfish gene)
From Biology 7th ed. by Campbell et alfig 19.14
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Genes are replicators (selfish gene) Transposons
mobile DNA
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• Five Perceptions of Genes
• Genes act as units of heredity
• Genes are seen as a cause of disease
• Genes code for proteins
• Genes act as switches, controlling development
• Genes are replicators (selfish gene)

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We did NOT cover this in class. I left it in if
you are interested in learning more about it.
This article in Nature has some good info
The RNA Worldpg 312
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Fig 7.5 8.2
This subtle difference in structure has profound
effects.
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Fig 7.8
Connect nucleotides by covalent bond
strand (notice 5-3 bond)
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Fig 8.11
DNA stores information, but does not do anything.
The information must be expressed to be useful.
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Fig 8.11
Where did this system come from?
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Was RNA the first biological molecule?
The RNA Worldpg 312
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Living organisms must fit all of the following
criteria (modified from Campbell Biology) 1.
They must have organization. 2. They must have
metabolism. 3. They must respond to the
environment. 4. They must be able to reproduce
themselves.
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Fig 8.2
U
RNA structure
A
G
C
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RNA can form base pairs within single stranded
molecule
Fig 8.109.12
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RNA can form complex 3-D structures
Ribosomes (rRNA) have enzymatic
activity Enzymatic RNAribozyme
Fig 9.12
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Some RNA molecules have catalytic activities
pg 223
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Living organisms must fit all of the following
criteria (modified from Campbell Biology) 1.
They must have organization. 2. They must have
metabolism. 3. They must respond to the
environment. 4. They must be able to reproduce
themselves.
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RNA can (theoretically) be replicated using
complementary bases
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Experimental determination of RNAs ability to
self-ligate A step towards self-replication
from Freemans Biological Science (2002)
chapter 3
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Q Can RNA self-ligate? Hypos Yes. No.
from Freemans Biological Science (2002)
chapter 3
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Column Chromatography
RNAs added in aqueous solution
Some, with tag, bind to column
Without tag, flow thru
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Overall RNA self-ligation improves by selection
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Theoretical evolution of self-replicating RNA
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Hypothetical Origin of Life
pg 214