Download DNA Basics

DNA Basics
WARM-UP #7
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
Phosphate
Group
O
O=P-O
O
5
CH2
O
N
C1
C4
Sugar
(deoxyribose)
C3
C2
Nitrogenous base
(A, G, C, or T)
A HISTORY OF DNA
SEE p. 292-293
• 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
“Rungs of ladder”
Nitrogenous
Base (A,T,G or C)
“Legs of ladder”
Phosphate &
Sugar Backbone
DNA Double Helix
5
O
3
3
P
5
O
O
C
G
1
P
5
3
2
4
4
2
3
P
1
T
5
A
P
3
O
O
P
5
O
3
5
P
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.
T
A
G
C
Nitrogenous Bases
• PURINES
1. Adenine (A)
2. Guanine (G)
A or G
• PYRIMIDINES
3. Thymine (T)
4. Cytosine (C)
T or C
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.
T
A
G
C
BASE-PAIRINGS
H-bonds
G
C
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…
See p. 297
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 See p. 298
DNA Replication
• Semiconservative
Model:
1. Watson and Crick
showed: the two strands of
DNA separate, and each
functions as a template for
synthesis of a new
complementary strand.
.
DNA Template
Parental DNA
New DNA
Replication Quiz
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
1. Why is replication necessary?
So both new cells will have the correct DNA
2. When does replication occur?
During interphase (S phase).
3. Describe how replication works.
Enzymes unzip DNA and complementary
nucleotides join each original strand.
4. Use the complementary rule to
create the complementary strand:
A---T
G---C
C---G
T---A
A---T
G---C
A---T
G---C
C---G
A---T
G---C
T---A
(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.
See p.301
• Both DNA & RNA are
formed from
NUCLEOTIDES and are
called NUCLEIC acids.
DNA Translation
• The cell uses
information from
“messenger” RNA to
produce proteins
See p.304-305
We will discuss
details of this on
a later date
1.
2.
3.
4.
5.
6.
Transcription/Translation Quiz
Why is transcription necessary?
Describe transcription.
Why is translation necessary?
Describe translation.
What are the main differences between
DNA and RNA.
Using the chart on page 303, identify
the amino acids coded for by these
codons:
UGGCAGUGC
1. Why is transcription necessary?
Transcription makes messenger RNA (MRNA) to
carry the code for proteins out of the nucleus to
the ribosomes in the cytoplasm.
2. Describe transcription.
RNA polymerase binds to DNA, separates the
strands, then uses one strand as a template to
assemble MRNA.
3. Why is translation necessary?
Translation assures that the right amino acids are
joined together by peptides to form the correct
protein.
4. Describe translation.
The cell uses information from MRNA to
produce proteins.
5. What are the main differences between DNA
and RNA.
DNA has deoxyribose, RNA has ribose; DNA
has 2 strands, RNA has one strand; DNA has
thymine, RNA has uracil.
6. Using the chart on page 303, identify the
amino acids coded for by these codons:
UGGCAGUGC
tryptophan-glutamine-cysteine
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)