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DNA and RNA
Chapter 12
Hereditary Material
• Genes code for PROTEINS!
• Genes are found on chromosomes.
• Chromosomes are made up of DNA.
Chromosome Structure
• Chromatin is tightly coiled around proteins
called histones.
• DNA and histone molecules form a
beadlike structure: nucleosome
• Nucleosomes create the supercoils
of DNA in a chromosome.
Chromosome Structure
of Eukaryotes
Nucleosome
Chromosome
Coils
Supercoils
DNA
double
Histones
helix
Structure of DNA
• In eukaryotes, DNA is found in the
NUCLEUS of cells.
• DNA is made up of a series of monomers
called nucleotides.
Nucleotide structure:
1. 5–carbon sugar: Deoxyribose
2. Phosphate group
3. Nitrogen base
• DNA is a twisted-ladder called a
DOUBLE HELIX!
DNA Nucleotide
Phosphate
Group
O
O=P-O
O
5
CH2
O
N
C1
C4
Sugar
(deoxyribose)
C3
C2
Nitrogen base
(A, G, C, or T)
Nitrogen Bases
• Double ring PURINES
Adenine (A)
Guanine (G)
A or G
• Single ring PYRIMIDINES
Thymine (T)
Cytosine (C)
T or
C
Chargaff’s (Base Pairing) Rule
• Adenine must pair with Thymine
• Guanine must pair with Cytosine
• Hydrogen bonds hold them
together
Why do they
pair together
this way?
T
A
G
C
DNA Double Helix
“Rungs of ladder”
Nitrogen Base
(A,T,G or C)
“Legs of ladder”
Phosphate &
Sugar Backbone
DNA Structure
Nucleotide
Hydrogen
bonds
Sugar-phosphate
backbone
Key
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
DNA Replication
• Occurs during cell division. (What phase of cell cycle?
WHY does this process happen?)
• Helicase “unzips” DNA, breaking the
hydrogen bonds.
• DNA polymerase bonds free nucleotides
together
– Complementary bonding only (A-T/G-C)
– Checks for errors
DNA Replication is
SEMI-CONSERVATIVE!
DNA Replication
New strand
Original
strand
DNA
polymerase
Growth
DNA
polymerase
Growth
Replication
fork
Replication
fork
New strand
Original
strand
Nitrogenous
bases
The History of DNA
The important
scientists to know!
Griffith’s “Transformation” Experiment
• One strain of bacteria was “transformed”
into another strain.
Avery’s experiment isolated the element that
caused the bacterial to become lethal…DNA
Hershey-Chase Experiment
Section 12-1
Bacteriophage with
phosphorus-32 in
DNA
Phage infects
bacterium
Radioactivity inside
bacterium
Bacteriophage with
sulfur-35 in protein
coat
Phage infects
bacterium
No radioactivity inside
bacterium
DNA is confirmed to be the genetic material.
Chargaff and Franklin
• Chargaff
Percentages of C/G and A/T bases are almost
equal in any sample of DNA
All organisms followed this rule
• Rosalind Franklin
X-Ray picture showed that
DNA was twisted into a
double helix.
Watson and Crick
• Discovered the molecular structure of DNA
RNA and Protein Synthesis
Section 12-3
RNA
•
•
•
•
•
•
Long, single strand (not a helix)
Nitrogen bases: A,U,G,C (no Thymine!)
Sugar: Ribose
Location: cytoplasm and nucleus
Types: messenger, transfer, ribosomal
Function: Makes proteins!!
Protein Synthesis occurs in two phases:
TRANSCRIPTION
TRANSLATION
Transcription
• Location where it occurs: Nucleus
• RNA polymerase will unwind DNA at the
region to be transcribed.
• It locates and binds at the promoter. (site on
DNA to start transcription)
Transcription
Animation
• mRNA is then made by base-pairing:
If DNA sequence is:
GATTACA
Then mRNA sequence is: CUAAUGU
• When finished, mRNA leaves the nucleus
and goes to the cytoplasm.
Section 12-3
Transcription
Adenine (DNA and RNA)
Cystosine (DNA and RNA)
Guanine(DNA and RNA)
Thymine (DNA only)
Uracil (RNA only)
RNA
polymerase
DNA
RNA
Translation
Location: Cytoplasm mRNA finds a ribosome
Ribosome reads strand for the start “codon”
A codon is a mRNA triplet. Ex: AUG, UUC, etc
Start codon is: AUG
Transfer RNA’s bring
amino acids to
ribosome.
Translation continued…
• tRNA’s anticodon bonds with mRNA
codon.
mRNA codons
AUG UAA CGC
tRNA anticodons UAC AUU GCG
• Amino acids connected with peptide
bonds.
• When a “Stop” codon is reached. Protein
is released from ribosome.
Translation
Section 12-3
Animation
How to Interpret
m-RNA’s Code:
• Each 3 nitrogen base sequence is called a
CODON.
• Each codon specifies for a particular amino
acid.
• AUG codon starts the initiation of the protein
and codes for the amino acid methionine.
• Stop codons do not code for any amino acids
ending the protein chain.
• A polypeptide is a chain of amino acids joined
with peptide bonds – aka a PROTEIN!
Codon Chart #1
Codon Chart #2
Section 12-3
Let’s Practice!
DNA:
mRNA:
tRNA:
TACTTGGAT
AUGAACCUA
UACUUGGAU
AA Sequence: Methionine, Asparagine, Leucine
Mutations
Section 12-4
Mutations
• Changes that occur in the DNA
• Two types:
1. Gene mutations
2. Chromosomal mutations
• Many mutations are harmless
• Pros: increase adaptation or survival
• Cons: some can be lethal or debilitating
Gene Mutations
• Changes that occur in a single gene.
• Point mutations: one nucleotide that
affects one amino acid.
(substitutions produce point mutations)
• Frameshift mutations: involve the
reading of the DNA or m-RNA strand;
many amino acids are affected.
(insertion or deletions produce frameshift mutations)
Gene Mutations
Frameshift mutations
Point mutation:
Substitution
Insertion
Deletion
Chromosomal Mutations
• Whole chromosome is affected.
• Four types:
1. Deletion – loss of material
2. Duplication – addition of material
3. Inversion – rearrangement of material
4. Translocation – switching material with
another chromosome
Chromosomal Mutations
Deletion
Duplication
Inversion
Translocation