Download Energy Transfer in Living Things (Chapter 6)

DNA
Discovery
Structure
Replication
Central Questions
• What were the roles of Rosalind
Franklin, James Watson and Francis
Crick in determining the structure of
DNA?
• What are the three parts to a
nucleotide?
• What is base pairing? What pairs with
what?
• How does DNA replicate?
What is DNA?
Discovering DNA’s Importance
DNA = deoxyribonucleic acid
• 1928- Griffith- ‘something’
transferred traits
• 1944- Avery identified DNA as the
transforming factor
• 1952- Hershey and Chase
confirmed Avery’s results by
radioactive tagging
What does that mean?
Discovery Continued
• 1950’s
–Rosalind Franklin got an ‘X’
pattern from X-ray
crystallography of DNA
–Chargaff figured out base pairing
(A to T and C to G)
Chromosomes
• Chromosomes are long strands of
DNA which contain many genes.
• They are the largest genetic
structures.
• 1952- Watson and Crick submit
model of DNA shape
1
Chromosomes
You have two copies of each
chromosome, each pair with the
same loci, but not necessarily same
copy of the gene
Locus (loci) is a
location on the
chromosome
which carries a
particular gene
DNA Structure
• DNA is made of two
connected chains of
nucleotides wound into a
double helix
• Double – two strands
Helix- spiral
• Looks like a twisted ladder
Genes
• A gene is a unit of DNA that codes for
a polypeptide (protein chain).
• Genes can have several parts:
–Promoter: controls where and when the
gene is expressed
–Open Reading Frame: coding sequence
of the gene
–Terminator Sequence: ends transcription
–Enhancer: areas other than promoter
than can ‘up production’
Nucleotide Structure
• Made of nucleotides
• Nucleotides are
made of:
Crick’s
sketch
Nucleotides Continued
• There are 4 DNA bases:
Adenine (A), Thymine (T),
Cytosine (C) and Guanine (G)
• In RNA Uracil (U) pairs with
Adenine
o Phosphatebackbone
o Sugar-deoxyribose
or ribose
o Base-gives the
‘letter’; the code
part
Base Pairing
• Each base is attracted to one
other base by Hydrogen Bonds
• Because of this bases ‘pair’ with
‘complementary’ bases
• Purines (A & G) pair with
pyrimidines (T & C)
–A pairs with T (U in RNA)
–G pairs with C
2
DNA Structure
• Nucleotides link into long
chains (polymers)
• These chains can be
described by their
sequence of bases
–ATGACG
• Because of base pairing we
know the other strand
DNA Structure
• Nucleotides link into long
chains
• These chains can be
written based on their base
sequence
–ATGACG
• Because of base pairing
we know the other strand
–TACTGC
–?
DNA Replication
1. Enzymes break hydrogen bonds
DNA Replication
3. Free nucleotides pair to open strands
DNA Replication
2. Strands ‘unzip’
DNA Replication
4. Two complete strands are made
3
DNA Replication
• Both strands made are
identical
• Half of each strand is
old, half is new
• Therefore we say DNA
replication is ‘Semiconservative’
replication
Who presented the model of
DNA structure we currently
use?
A
B
C
D
Jones and Thomas
Jackson and Gray
Franklin and Avery
Watson and Crick
What base pairs with T?
A
B
C
D
C
A
G
U
Central Questions
• What were the roles of Rosalind
Franklin, James Watson and Francis
Crick in determining the structure of
DNA?
• What are the three parts to a
nucleotide?
• What is base pairing? What pairs with
what?
• How does DNA replicate?
What of the following make
up nucleotides?
A Base, sugar, phosphate
B DNA, protein, sugar
C Amino acids, carbon and
water
D Sugar, phosphate and
water
What do we call the structure
of DNA strands?
A
B
C
D
Twisted matrix
Double Helix
Hydrogen Bonding
Single Helix
4
What is NOT a step in DNA
replication?
A
B
C
D
Hydrogen Bonds break
Molecule ‘unzips’
Free nucleotides pair
New sugars are added
5