DNA
Module B: Bio . B.1
Describe the sculpture
Bio. B.1.2: Explain how genetic
information is inherited
• Bio.B.1.2.1-Describe how the process of DNA replication
results in the transmission and/or conservation of
genetic material.
Before we get started…
• What is genetics?
• What is the genetic material?
The Role of DNA:
•What is the role of DNA in heredity?
•DNA must be capable of:
1. Storing information
2. Copying information
3. Transmitting information
DNA stores information
DNA copies and
transmits information
DNA is made of nucleotides
• Nucleotides are the building blocks of DNA
• Nucleotides composed of:
1. Phosphate
2. Sugar (deoxyribose)
3. Nitrogen Base
•
•
•
•
Adenine (A)
Guanine (G)
Cytosine (C)
Thymine (T)
Nucleotides link together
STRUCTURE of DNA
Chargaff:
•Chargaff’s Rule:
• percentages of A (adenine) and T(thymine)
were equal in many sample of DNA
• percentages of C (Cytosine) and G (Guanine)
were also equal
STRUCTURE of DNA
Chargaff’s Data
If a species has 35% adenine in its DNA, what is the
percentage of the other three bases? Can you figure it
out?
STRUCTURE of DNA
Rosalind Franklin
• X-ray picture of DNA
• DNA had two strands that twisted
around each other like a coil
STRUCTURE of DNA
Watson and Crick
• James Watson and Francis Crick built a three
dimensional model of DNA
•
•
•
•
Shape of the DNA = double helix.
Strands run in opposite direction (anti-parallel)
Base pairing rules (A pairs with T; C pairs with G)
Strands held together by hydrogen bonds
Watson TED talk
Antiparallel DNA Strands:
What happens to the DNA
structure during S phase?
• DNA replicates (duplicates, is copied, etc.)
• Watson and Crick’s 3D model immediately proposed a
replication mechanism
animation
DNA Replication:
•DNA gets copied during interphase
•Ensures that each resulting cell has the same
complete set of DNA
•Each strand has all the information needed
to construct the other strand
Process of DNA Replication:
1. DNA is “unzipped” or separated
• Enzyme = helicase
• Breaks hydrogen bonds that hold the two
strands of DNA together
Process of DNA Replication:
2. New strands are built
• Enzyme = DNA polymerase
• Joins individual nucleotides together to produce
a new strand of DNA that is complementary to
the other
• Proofreads each new strand
How is replication
different in prokaryotes?
• In eukaryotes, replication begins at many different
locations and proceeds in both directions until
each chromosome is completely copied
• In prokaryotes, replication begins at one point and
proceeds in two directions until the entire
chromosome Is copied
DNA
Replication
Prokaryotes
Vs
eukaryotes
Quick Check
1. A nucleotide does not contain
A.
B.
C.
D.
A 5-carbon sugar
An amino acid
A nitrogen base
A phosphate group
Quick Check
2. According to Chargaff’s rule of base pairing which of
the following is true about DNA?
A. A=T and C=G
B. A=C and T=G
C. A=G and T=C
D. A=T=G=C
Quick Check
3. The bonds that hold the two strands of DNA
together come from
A. The attraction of phosphate groups for each other
B. Strong bonds between nitrogenous bases and the
sugar-phosphate backbone
C. Weak hydrogen bonds between bases
D. Carbon-to-carbon bonds in the sugar portion of the
nucleotides
Quick Check
4.
A.
B.
C.
D.
In prokaryotes, DNA molecules are located in the
Nucleus
Ribosomes
Cytoplasm
histones
Quick Check
5. In eukaryotes, nearly all the DNA is found in the
A. Nucleus
B. Ribosomes
C. Cytoplasm
D. histones
Quick Check
6. The main enzyme involved in linking individual
nucleotides into DNA molecules is
A. DNA protease
B. Ribose
C. Carbohydrate
D. DNA polymerase
PREC-CLASS…
All of the parts of a cell are
controlled by the information
in DNA, yet DNA does not leave
the nucleus. How do you think
the information in DNA might
get from the nucleus to the
rest of the cell?
Central Dogma of Molecular Biology
Describes flow of information from DNA to protein
transcription
DNA
translation
RNA
RNA is the link
between DNA
and proteins.
Protein
Analogy for central
dogma
The master plan has all the information
needed to construct a building.
Analogy for central
dogma
But builders never bring a valuable master
plan to the building site where is might be
damaged or lost.
Analogy for central
dogma
Instead, builders work from blueprints,
inexpensive disposable copies of the master
plan.
Analogy for central
dogma
Master plan = DNA
Building site = ribosomes (in cytoplasm)
Blueprint copies = RNA
DNA vs RNA
RNA
DNA
• Single stranded
• Double stranded
• Made of nucleotides
• Made of nucleotides
• Sugar = ribose
• Sugar = deoxyribose
• Bases = U instead of T
• Bases = C,G, A, T
Different types of RNA
1. Messenger RNA – carries the instructions from DNA to
cytoplasm on how to make the protein
2. Ribosomal RNA – form ribosomes in cytoplasm to help
build the protein
3. Transfer RNA – delivers the amino acids needed to
build the protein
Transcription (RNA synthesis)
• DNA  RNA
• Occurs in the nucleus
• Requires RNA polymerase
• Builds RNA strand
• Uses one strand of DNA as template
• Involves single gene
• Produces MANY RNA copies
RNAi Video
Replication vs Transcription
•Replication copies the entire DNA
•Transcription only copies one gene
•Replication only makes one copy
•Transcription makes many copies
•BOTH involve complex enzymes
•BOTH follow complementary base pairing
•BOTH occur in the nucleus
If you were given the sequence of a DNA strand, could you
figure out the sequence of the mRNA strand?
Remember, U instead of T in RNA!!!
For example:
DNA
T ACGC CCTATTGAT
mRNA ??
A U G C G G G A UA AC U A
Central Dogma of Molecular Biology
Describes flow of information from DNA to protein
transcription
DNA
translation
RNA
Protein
Translation (protein synthesis)
• RNA  protein
• Occurs in the cytoplasm
• Involves ribosome, mRNA, tRNA and amino acids
• RNA is “translated” into amino acid sequence
The language of protein synthesis
• Language of RNA = nucleotides
• Language of protein = amino acids
• Triplet code: three mRNA bases (codon) code for one
amino acid
Genetic Code:
• Codon = a group of three nucleotide bases in the mRNA
that codes for a particular amino acid
Genetic Code: (mRNA codon to amino acid)
Genetic Code
• START codon signals the start of translation
• AUG
• also codes for methionine
• STOP codons signal stop of translation
• UGA, UAA, UAG
• Do not code for any amino acid
Genetic Code = common language
• UNIVERSAL – shared by all organisms
• REDUNDANT – more than one codon may code for the
same amino acid
• Allows flexibility if mistakes are made
Quick Check
• A certain gene has the following base sequence:
• GACAAGTCCAATC
• Write the sequence of the mRNA molecule transcribed
from this gene
• Divide you mRNA sequence into codons
• How many codons?
• What amino acid does each codon code for?
• How many amino acids?
QUICK CHECK…
Remember, U instead of T in RNA!!!
For example:
DNA
mRNA ??
Amino acids
T A C G C C C T A T T G A T A
The role of ribosomes in translation
• Ribosomes act as the machinery
• Ribosomes use the sequence of codons in mRNA to
assemble amino acids into protein chains
The role of tRNA in translation
• Each tRNA molecule carries one kind of amino acid
• Anticodon on tRNA recognizes complementary codon on
mRNA
• For example, tRNA for methionine has the anticodon UAC
which pairs with the methionine codon (AUG)
Process of Translation
1. Ribosome binds to mRNA
2. mRNA codons attract complementary tRNA anticodons
3. peptide bond forms between amino acids then breaks
bond holding the amino acid to the tRNA
4. Empty tRNA leaves; the ribosome pulls the mRNA
exposing the next codon
QUICK CHECK…
Remember, U instead of T in RNA!!!
For example:
DNA
T A C G C C C T A T T G A T A
mRNA ??
Amino acids
tRNA
Central Dogma of Molecular Biology
Describes flow of information from DNA to protein
transcription
DNA
translation
RNA
Protein
Mutations are changes in the DNA
1. Gene mutations (single gene)
2. Chromosomal mutations (multiple genes involved)
mutated
base
1. Gene Mutations
• Also known as point mutations because they occur at
a single point in the DNA sequence
• Occur during replication
• Different types
A. Substitutions
B. Insertions and deletions
A. Substitutions
• One base is changed to a different base
• Only affect one amino acid
• Sometimes have no effect (silent)
• EX: changing mRNA codon from CCC to CCA
• Codon still specifies proline; SILENT
• EX: changing mRNA codon from CCC to ACC
• Replaces proline with threonine
B. Insertions and
Deletions
• Frameshift mutations – “shift” the reading frame
• Effects are dramatic
• Can change every amino acid after the mutation
Frameshift
Mutations
2. Chromosome mutations
• Changes in number or structure of chromosomes
• Occur during meiosis
• Four types
A.
B.
C.
D.
Deletion (loss of all or part of a chromosome)
Duplication (extra copy)
Inversion (reverse in the direction of a chromosome)
Translocation (one chromosome attaches to another)
Mutagens
• Chemical or physical agents in the environment that
can cause mutations in DNA
• Include
• Pesticides, tobacco, environmental pollutants, UV light,
X-rays
Harmful and Helpful
Mutations
Mutations can be harmful if…
• They cause drastic changes in the protein that is
produced
• Defective proteins can disrupt normal function
• Ex: sickle cell anemia, some cancer
Harmful and Helpful
Mutations
Beneficial effects
• Variation produced by mutations can be highly
advantageous to organisms in different or changing
environments
• Responsible for evolution
• EX: pesticide resistance (bad news for humans but good
news for mosquitoes)
• EX: human resistance to HIV