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DNA and RNA
Chapter 12
Hereditary Material
• Genes are protein
codes.
• Our genes are on
our chromosomes.
• Chromosomes are
made up of DNA.
• Genes are
composed 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
Chromosome
Nucleosome
DNA
double
helix
Coils
Supercoils
Histones
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. Nitrogenous 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
Nitrogenous base
(A, G, C, or T)
Nitrogenous 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
Why do
they pair
together
this way?
• Adenine must pair with
Thymine
• Guanine must pair with
Cytosine
• The bases form weak
hydrogen bonds
T
A
G
C
DNA Double Helix
“Rungs of ladder”
Nitrogenous
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.
• Helicase enzyme “unzips” the molecule
of DNA, breaking the hydrogen bonds.
• Free-nucleotides in the nucleus will be
bonded with its complementary base.
• DNA polymerase helps to bond the
nucleotides together and check for errors.
DNA Replication
Section 12-2
New strand
Original
strand
DNA
polymerase
Growth
DNA
polymerase
Growth
Replication
fork
Replication
fork
New strand
Original
strand
Nitrogenous
bases
DNA Replication
The Scientists
• Griffith – one strain of bacteria was
“transformed” into another strain.
• Avery – found that DNA was the
transforming factor.
• Hershey and Chase – DNA is the genetic
material.
• Watson and Crick – discovered the
molecular structure of DNA.
Griffith’s “Transformation”
Experiment
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
Chargaff and Franklin
• Chargaff
Percentages of guanine and cytosine bases are
almost equal in any sample of DNA
Same is true of adenine and thymine
DNA in all instances and from all organisms
followed this rule
• Rosalind Franklin
X-Ray diffraction showed that
DNA was twisted into a
double helix.
RNA and Protein Synthesis
Section 12-3
RNA
•
•
•
•
•
•
Long, single strand of nucleotides.
Nitrogen bases: A,U,G,C no Thymine!
Sugar: Ribose
Found in cytoplasm and nucleus
Types: messenger, transfer, ribosomal
Function: Involved in the synthesis of
protein molecules.
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.
• mRNA is then made by base-pairing:
A-U, G-C, T-A, C-G
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
Section 12-3
Codon Chart #2
Let’s Practice!
DNA:
mRNA:
tRNA:
TACTTGGAT
AUGAACCUA
UACUUGGAU
Amino Acid squence:
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