MLB 111 UNIT 5
STUDY UNIT 5: DNA and its role in heredity (4 lectures)
STUDY MATERIAL: Hillis et al., parts of Chapter 13 (see core concepts below)
Lecturer: Dr Markus Wilken
Core Concepts:
● Section 13.1 Experiments revealed the function of DNA as genetic material (review only
- not asked much)
● Section 13.2 DNA has a structure that suits its function - go read through in slideshow
● Section 13.3 DNA is replicated semi-conservatively
● Section 13.4 Errors in DNA can be repaired
●Section 13.5 The Polymerase Chain Reaction amplifies DNA|
LEARNING OUTCOMES:
You have mastered this study theme when you can:
1. Name the four bases that form the building blocks for DNA.
Adenine (A)
Thymine (T)
Guanine (G)
Cytosine (C)
2 rings - purines: A and G
1 ring - pyrimidines: C and T
The grooves are important for access to DNA. Shape of DNA is double helix. The important
part of DNA is the bases, not the "backbone" (sugar-phosphate).The DNA loops around once
for every 10 base pairs. DNA molecules are always 2nm wide.
2. Explain the work of Chargaff and colleagues and the importance of this to DNA
structure.
In 1950's - Chagraff and others found that in all DNA, the number of purines = number of
pyrimidines. But the relative abundance of A + T vs G + C varies among species.
3. Describe the structure of DNA with respect to the following:
(a) How the Chargaff rules are satisfied.
The model by Crick and Watson pairs purines on one strand with pyrimidines on the other,
resulting in uniform width.
(b) The nature of the phosphodiester bonds which link the nucleotides in a DNA chain.
1
,Sugar-phosphate backbone. Bond is phosphodiester bond (extremely rigid) that holds
backbone together.
(c) The forces that keep the strands of the double-helix together.
(d) The number of hydrogen bonds involved in A-T and G-C base pairing.
Hydrogen bonds are weak (across 1) bonds between nucleotides - interaction bonds.
3 for G-C
2 for A-T
(e) The direction of the complementary strands in the two strands of a DNA molecule.
5' to 3' and then 3' to 5'
Two backbones in opposite directions and will never cross: antiparallel.
The structure of DNA suits its function - the double-helix structure is essential to DNA
function:
• Millions of nucleotides store a huge amount of genetic information in the base order
• Susceptible to mutations
• Precise replication in cell division is possible by complimentary base pairing
• Genetic information is expressed as the phenotype
◦ Nucleotide sequences determine sequences of amino acids in proteins
◦ Proteins determine what you (everything) are
2
, Backbones closer together on one side forms minor groove.
Nucleotide polymers are always added in the 5' to 3' direction (relative to the new
DNA strand) by making a new phosphodiester bond through linking an incoming 5'
P to a free 3' OH
DNA is an antiparallel double-stranded helix.
4. Based on your knowledge of the structure of DNA, you should be able to carry out
calculations such as
(a) The percentage/amount of any nucleotide if the percentage/amount of one is provided
for a specific DNA molecule.
(b) The number of hydrogen bonds in a DNA molecule, the number of helix turns, the
number of bases (nucleotides), the number of base pairs, the number of phosphodiester
bonds, and the number of purines and pyrimidines.
Important to see document in notes section below.
5. Describe the three proposed models for DNA replication.
3
STUDY UNIT 5: DNA and its role in heredity (4 lectures)
STUDY MATERIAL: Hillis et al., parts of Chapter 13 (see core concepts below)
Lecturer: Dr Markus Wilken
Core Concepts:
● Section 13.1 Experiments revealed the function of DNA as genetic material (review only
- not asked much)
● Section 13.2 DNA has a structure that suits its function - go read through in slideshow
● Section 13.3 DNA is replicated semi-conservatively
● Section 13.4 Errors in DNA can be repaired
●Section 13.5 The Polymerase Chain Reaction amplifies DNA|
LEARNING OUTCOMES:
You have mastered this study theme when you can:
1. Name the four bases that form the building blocks for DNA.
Adenine (A)
Thymine (T)
Guanine (G)
Cytosine (C)
2 rings - purines: A and G
1 ring - pyrimidines: C and T
The grooves are important for access to DNA. Shape of DNA is double helix. The important
part of DNA is the bases, not the "backbone" (sugar-phosphate).The DNA loops around once
for every 10 base pairs. DNA molecules are always 2nm wide.
2. Explain the work of Chargaff and colleagues and the importance of this to DNA
structure.
In 1950's - Chagraff and others found that in all DNA, the number of purines = number of
pyrimidines. But the relative abundance of A + T vs G + C varies among species.
3. Describe the structure of DNA with respect to the following:
(a) How the Chargaff rules are satisfied.
The model by Crick and Watson pairs purines on one strand with pyrimidines on the other,
resulting in uniform width.
(b) The nature of the phosphodiester bonds which link the nucleotides in a DNA chain.
1
,Sugar-phosphate backbone. Bond is phosphodiester bond (extremely rigid) that holds
backbone together.
(c) The forces that keep the strands of the double-helix together.
(d) The number of hydrogen bonds involved in A-T and G-C base pairing.
Hydrogen bonds are weak (across 1) bonds between nucleotides - interaction bonds.
3 for G-C
2 for A-T
(e) The direction of the complementary strands in the two strands of a DNA molecule.
5' to 3' and then 3' to 5'
Two backbones in opposite directions and will never cross: antiparallel.
The structure of DNA suits its function - the double-helix structure is essential to DNA
function:
• Millions of nucleotides store a huge amount of genetic information in the base order
• Susceptible to mutations
• Precise replication in cell division is possible by complimentary base pairing
• Genetic information is expressed as the phenotype
◦ Nucleotide sequences determine sequences of amino acids in proteins
◦ Proteins determine what you (everything) are
2
, Backbones closer together on one side forms minor groove.
Nucleotide polymers are always added in the 5' to 3' direction (relative to the new
DNA strand) by making a new phosphodiester bond through linking an incoming 5'
P to a free 3' OH
DNA is an antiparallel double-stranded helix.
4. Based on your knowledge of the structure of DNA, you should be able to carry out
calculations such as
(a) The percentage/amount of any nucleotide if the percentage/amount of one is provided
for a specific DNA molecule.
(b) The number of hydrogen bonds in a DNA molecule, the number of helix turns, the
number of bases (nucleotides), the number of base pairs, the number of phosphodiester
bonds, and the number of purines and pyrimidines.
Important to see document in notes section below.
5. Describe the three proposed models for DNA replication.
3
