FCH 532 Lecture 4 Chapter 5: DNA. The Watson and Crick double helix model for DNA.
DNA (Deoxyribonucleic Acid)€¦ · DNA Replication •Semiconservative Model: 1. Watson and Crick...
Transcript of DNA (Deoxyribonucleic Acid)€¦ · DNA Replication •Semiconservative Model: 1. Watson and Crick...
DNA
(Deoxyribonucleic Acid)
Genetic material of cells…
• GENES – units of genetic material that
CODES FOR A SPECIFIC TRAIT
• Called NUCLEIC ACIDS
• DNA is made up of repeating molecules
called NUCLEOTIDES
DNA Nucleotide
O
O=P-O
O
Phosphate
Group
N Nitrogenous base
(A, G, C, or T)
CH2
O
C1 C4
C3 C2
5
Sugar
(deoxyribose)
A HISTORY OF DNA
• Discovery of the DNA double helix
A. Frederick Griffith – Discovers that a factor in diseased bacteria can transform harmless bacteria into deadly bacteria (1928)
B. Rosalind Franklin - X-ray photo of DNA.
(1952)
C. Watson and Crick - described the DNA molecule from Franklin’s X-ray.
(1953)
Watson & Crick proposed…
•DNA had specific pairing between the
nitrogen bases:
ADENINE – THYMINE
CYTOSINE - GUANINE
•DNA was made of 2 long stands of
nucleotides arranged in a specific
way called the “Complementary Rule”
DNA Double Helix
Nitrogenous
Base (A,T,G or C)
“Rungs of ladder”
“Legs of ladder”
Phosphate &
Sugar Backbone
DNA Double Helix
P
P
P
O
O
O
1
2 3
4
5
5
3
3
5
P
P
P O
O
O
1
2 3
4
5
5
3
5
3
G C
T A
Nitrogenous Bases
• PURINES
1. Adenine (A)
2. Guanine (G)
• PYRIMIDINES
3. Thymine (T)
4. Cytosine (C) T or C
A or G
Chargaff’s Rule
• Adenine must pair with Thymine
• Guanine must pair with Cytosine
• Their amounts in a given DNA molecule will be
about the same.
G C T A
BASE-PAIRINGS
C G
H-bonds
T A
Genetic Diversity… • Different
arrangements of
NUCLEOTIDES in a
nucleic acid (DNA)
provides the key to
DIVERSITY among
living organisms.
The Code of Life…
• The “code” of the chromosome is the
SPECIFIC ORDER that bases occur.
A T C G T A T G C G G…
DNA is wrapped tightly around
histones and coiled tightly to form
chromosomes
DNA Replication • DNA must be copied
• The DNA molecule produces 2 IDENTICAL new complementary strands following the rules of base pairing:
A-T, G-C
•Each strand of the original DNA serves as a template for the new strand
DNA Replication
• Semiconservative
Model:
1. Watson and Crick
showed: the two strands
of the parental molecule
separate, and each
functions as a template
for synthesis of a new
complementary strand.
. Parental DNA
DNA Template
New DNA
1. Why is replication necessary?
2. When does replication occur?
3. Describe how replication works.
4. Use the complementary rule to
create the complementary strand:
A---?
G---?
C---?
T---?
A---?
G---?
A---?
G---?
C---?
A---?
G---?
T---?
Replication Quiz
(1961) Watson & Crick proposed…
• …DNA controlled cell function by serving as a template for PROTEIN structure.
• 3 Nucleotides = a triplet or CODON
(which code for a specific AMINO ACID) See p.303
• AMINO ACIDS are the building blocks of proteins.
DNA Transcription
• DNA can “unzip” itself and RNA nucleotides match up to the DNA strand.
• Both DNA & RNA are formed from NUCLEOTIDES and are called NUCLEIC acids.
DNA Translation
• The cell uses information from “messenger” RNA to produce proteins
We will
discuss details
of this on a
later date
Transcription/Translation Quiz 1. Why is transcription necessary?
2. Describe transcription.
3. Why is translation necessary?
4. Describe translation.
5. What are the main differences
between DNA and RNA.
AMAZING DNA FACTS…
• DNA from a single human
cell extends in a single
thread for almost 2 meters
long!!!
• It contains information
equal to some 600,000
printed pages of 500 words
each!!!
(a library of about 1,000 books)
LET’S REVIEW DNA…
1. List the conclusions Griffith & Avery,
Hershey & Chase drew from their
experiments.
2. Summarize the relationship between
genes & DNA.
3. Describe the overall structure of the
DNA molecule.
4. What are the 4 kinds of bases?