Molecular Biology: DNA Structure and Function

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Questions and Answers

What did Chargaff demonstrate about the nucleotide composition of DNA?

Adenine always exceeds thymine in number.

Adenine equaled cytosine in quantity.

Guanine is present in higher amounts than cytosine.

The amount of adenine equals the amount of thymine. (correct)

What structure did Watson and Crick discover about DNA in 1953?

It is a single-stranded molecule.

It is composed of ribonucleotides.

It is a double helix. (correct)

It contains three strands.

What type of bonds connect nucleotides in a DNA polymer?

Hydrogen bonds

Van der Waals bonds

Phosphodiester bonds (correct)

Ionic bonds

Which of the following statements about purines and pyrimidines is true?

Purines consist of adenine and guanine. Signup and view all the answers

What was Levene's significant contribution to the understanding of DNA in 1910?

He demonstrated that DNA is a polymer of nucleotides. Signup and view all the answers

Which nitrogenous bases pair together in DNA?

Adenine with thymine and guanine with cytosine. Signup and view all the answers

What is the role of the 5'-PO4 group in nucleotide bonding?

It covalently bonds with the 3'-OH group of another nucleotide. Signup and view all the answers

What is the significance of Kossel's discovery regarding DNA?

He established that DNA contains four nitrogenous bases. Signup and view all the answers

What type of bonding connects nucleotides in a DNA strand?

Phosphodiester Bonds Signup and view all the answers

Which nitrogenous base pairs with thymine in DNA?

Adenine Signup and view all the answers

What does the term 'antiparallel' refer to in DNA structure?

The DNA strands run in opposite directions. Signup and view all the answers

Which base pairing rule is described by Chargaff's rules?

A pairs with T, G pairs with C Signup and view all the answers

What is the primary structure of DNA composed of?

A sugar-phosphate backbone Signup and view all the answers

How does DNA encode genetic information?

Using a long sequence of nucleotide bases Signup and view all the answers

What type of bond links adenine to thymine in DNA?

Two hydrogen bonds Signup and view all the answers

What do complementary base pairs in DNA allow for?

Replication of DNA Signup and view all the answers

What structural feature distinguishes DNA as a double helix?

Contains a minor groove and a major groove Signup and view all the answers

How is prokaryotic DNA structurally characterized?

Arranged in long loops attached to structural proteins Signup and view all the answers

Which of the following describes the compact structure of eukaryotic DNA?

Nucleosomes that form chromatin fibers of various diameters Signup and view all the answers

What is the role of the linker histone H1 in nucleosomes?

To link nucleosomes into a coiled structure Signup and view all the answers

Which characteristic of B-DNA is true?

It consists of two anti-parallel strands Signup and view all the answers

In terms of size, how does the human chromosome compare to the nucleus?

It is 14,000 times the size of the nucleus Signup and view all the answers

What is the approximate size of the bacterial chromosome in E. coli?

4.6 million base pairs Signup and view all the answers

What is a nucleosome composed of?

DNA wrapped around eight core histone proteins Signup and view all the answers

What term describes the tightly packed form of chromatin that remains condensed even during interphase?

Heterochromatin Signup and view all the answers

During which phase of the cell cycle does chromatin condense tightly?

M phase Signup and view all the answers

What is the primary function of the genes within mitochondrial DNA in eukaryotes?

Encode for enzymes involved in oxidative phosphorylation Signup and view all the answers

What are the regions of DNA called that provide instructions for controlling gene expression?

Regulatory regions Signup and view all the answers

Which of the following descriptions best fits euchromatin?

Loosely packed regions of chromatin that are transcriptionally active Signup and view all the answers

What term describes the phenomenon of chromatin changing structure during the cell cycle?

Chromatin remodeling Signup and view all the answers

What type of DNA is often found in circular form and may encode for traits like drug resistance in some bacteria?

Plasmid DNA Signup and view all the answers

What are the structural regions of chromatin that remain tightly packed even during interphase known as?

Heterochromatin Signup and view all the answers

What is one of the primary roles of cyclic nucleotide monophosphates like cAMP?

Cell signalling Signup and view all the answers

Which statement accurately describes the function of nucleotide triphosphates such as ATP?

They provide energy storage and transport. Signup and view all the answers

Which of the following is NOT a function of nucleotides?

Store genetic information Signup and view all the answers

What process occurs when a nucleotide triphosphate like ATP converts to ADP?

Energy release Signup and view all the answers

Coenzymes, such as NAD and coenzyme A, which are derived from nucleotides, primarily function in which biological process?

Cellular respiration Signup and view all the answers

What are the key requirements for genetic material?

Must contain complex information. Signup and view all the answers

What significant conclusion did Avery et al. reach about DNA?

DNA can transform non-pathogenic bacteria into pathogenic ones. Signup and view all the answers

Which year is associated with the discovery of nucleic acid in the nucleus?

1869 Signup and view all the answers

What is the definition of phenotype?

The physical expression of genes. Signup and view all the answers

Which molecule was the focus of investigation by Avery et al. in their experiments?

DNA Signup and view all the answers

What was a conclusion of the tetranucleotide theory proposed by Levene?

DNA consists of a repeated sequence of four nucleotides. Signup and view all the answers

Before the 1950s, how was genetic material generally identified?

By determining its ability to store complex information. Signup and view all the answers

What type of bacteria did Avery et al. use in their genetic transformation experiments?

S.pneumoniae Signup and view all the answers

Study Notes

Molecular Genetics (BHS016-1)

Course delivered by Dr Taiwo Shittu
Course code: BHS016-1

Nucleic Acids (BHS016-1 Topic 1)

Learning Outcomes:
- Students should be able to recall the chemical structure and key components of nucleotides.
- Explain the formation of nucleic acids from individual nucleotides.
- Describe the 3D structure of DNA.
- Understand the various functions of nucleic acids and nucleotides.

What Is Genetics?

Genetics is the study of heredity.
Heredity is controlled by genes.
Genes are units of biological information.
Genes are units of inheritance.

Why Is Genetics Important?

Genetics plays a role in various fields:
- Biomedical science (e.g., heart damage from faulty genes).
- Biological science (e.g., extracting genetic information from ancient rhino teeth).
- Forensic science (e.g., genetic evidence in unsolved rape cases).

Basic Structure Of The DNA Molecule (Page 6)

This section likely describes the fundamental composition of the DNA molecule.

How To Identify Genetic Material? (Page 7)

Genetic material was unknown prior to 1950s.
- Genetic material must contain complex information.
- Genetic material must replicate faithfully.
- Genetic material must encode the phenotype.
Definition: Phenotype

How Do We Know It Is DNA? (Page 8)

Nucleic acids were discovered in the nucleus (1869).
Histone proteins were discovered in the nucleus (1884).
The nucleus was shown to carry genetic material (1887).
Questions about the genetic material in chromatin (i.e., whether DNA or proteins).
Tetranucleotide theory misled the conclusion (Levene 1910).
Truth was realised in 1944 (Avery et al.).
Definition: Chromatin

Timeline Of DNA As Genetic Code (Page 9)

Presents a timeline of significant discoveries related to DNA's role as the genetic code.
- Includes dates and researchers/experiments associated with key stages in DNA research.

How Do We Know It Is DNA? (Page 10)

Avery et al. worked with two types of Streptococcus pneumoniae bacteria—S and R strains
S strain: virulent (caused disease in mice).
R strain : non-virulent (did not cause disease in mice).
Heating and killing the S strain of bacteria meant they couldn't cause disease anymore
Combining dead S strain with living R strain transformed living R strain into virulent S strain

1944 – Avery, Macleod, And McCarty (Page 12, 13)

Experiment aimed at identifying the chemical nature of the transforming substance, which was found to be DNA
- Different enzymes such as RNase, Protease, and DNase were used during different stages of the transformation process to determine chemical components responsible for the transformation.
Conclusion: DNase alone destroyed the transformation substance, suggesting that DNA was the transforming substance.

How Can DNA Carry Information? (Page 14, 15, 16, 17, 18)

1800s—Kossel showed DNA contained four nitrogenous bases.
Definition: Purine, Pyrimidine.

How Can DNA Carry Information? (Page 17)

1948 – Chargaff demonstrated DNA contained fixed ratios of nucleotides.
- Different organisms had different ratios. -(A+G) = (T+C) for all DNA samples

How Can DNA Carry Information? (Page 19)

1953 – Watson and Crick discovered DNA is a double helix.
Human chromosomes are linear, with two complementary and antiparallel strands forming a helical shape

Primary Structure of DNA (Pages 20, 21, 22, 23)

Nucleotides join to form polymers by phosphodiester bonds.
- Phosphodiester bond forms between the 5' phosphate group of one nucleotide to the 3' hydroxyl group of another nucleotide
Covalent bonding of nucleotides produces a sugar-phosphate backbone
Definition: Covalent, 5' prime, 3' prime.

Secondary Structure of DNA (Page 24, 25, 26)

Chargaff's rules: base pairing
- Bases pair by hydrogen bonding—A with T, G with C
  - Two H-bonds link A to T.
  - Three H-bonds link G to C.
- Definition: H-bond.
- Linear polynucleotide strands pair to form a double stranded molecule.
- Complementary base pairing

Summary of Basic DNA Structure (Page 27)

DNA consists of two polynucleotide strands
- Each strand: sugar-phosphate backbone.
- Nitrogenous bases on the inside.
- Hydrogen bonds join bases of two strands.
- A-T, G-C pairing.
- Two polynucleotide strands are complementary and antiparallel.

How Can DNA Carry Information? (Page 28)

Genetic material must contain complex information.
- Extremely long sequences of nucleotide
Genetic material must replicate faithfully.
- Complementary base pairing means each strand serves as template for the production of a new strand.
Genetic material must encode the phenotype.

Tertiary Structure of DNA (Page 29)

This section likely deals with the 3D arrangement of a DNA molecule.

DNA is a Double Helix (Page 31)

5'-3' phosphodiester bonds cause torsional force that twists the double stranded DNA molecule.
Forms an alpha helix
DNA has two anti-parallel chains
- Right-handed helix
- Major and minor grooves

B-DNA Structure (Page 32)

The DNA backbone is formed from deoxyribose sugars linked by phosphates.
Key structural features include the major and minor grooves.
Specific dimensions of the double helix are described (e.g., diameter, distance between base pairs).

DNA Requires Further Packing (Page 33)

In cells: each double-stranded DNA molecule forms a structure called a chromosome.
Bacterial chromosome (E. coli) is 4.6 million base pairs long (1000x longer than the bacterial cell)
Human nuclei contain 3.2 billion base pairs (3230 Mbp) (14000 x longer than the nucleus)

Prokaryote DNA Simple Structure (Page 34)

Prokaryotes (bacteria) typically have a single chromosome with a simple structure.
- DNA is mostly folded into long loops, held in place by structural proteins.

Bacterial DNA Folded In Twisted Loops (Page 35)

Visual representation of bacterial DNA folding and looping

Eukaryotic DNA Shows Complex Packing (Page 36)

Eukaryotic DNA displays a more complex packing structure compared to prokaryotic DNA
DNA packing involves several hierarchical levels, starting from the double helix to the chromosome.
- Dimensions at each level of packing are shown

Double Helix Packed Into Nucleosomes (Page 37)

160-200 base pairs of DNA are wrapped around eight core histone proteins.
Nucleosomes are linked together by linker histone, H1.

Nucleosomes Packed Into 30 nm Fibre (Page 38)

Nucleosomes are further organized into a 30 nm fiber ("beads on a string").
This section depicts the structure

30 nm Fibre Packed Into Larger Coils (Page 39)

30nm fiber further coils into larger structures like 300nm, then 700nm fibres
Scaffold proteins are likely involved in the organization of these higher-order coils

700 nm Coiled Coil Forms Chromosome (Page 40)

This describes further coiling of the 700nm filament into the structure of a chromosome.

Eukaryotic DNA Shows Complex Packing (Page 41)

DNA is wound around histone proteins to form nucleosomes, which lead to a 30nm fiber
Packing results in the 700nm coiled coil that forms a chromosome.

DNA Packing Alters During Cell Cycle (Pages 42, 43)

During interphase: chromatin regions are loosely packed (euchromatin).
- Transcriptionally active regions (codes for proteins & RNAs)
During M-phase: chromatin is tightly packed (heterochromatin).
- Includes centromeres & telomeres.

Functions of DNA and Nucleotides (Pages 44, 45, 46, 47, 48)

DNA functions include:
- Provide instructions for building proteins (e.g. genes).
- Control protein expression using regulatory regions.
- Includes non-coding DNA whose function is still unknown.
Other DNA types (e.g. mitochondrial, chloroplast) and their specific functions are described.
Nucleotide functions described
- Cyclic Nucleotide Monophosphates (signaling molecules like cAMP)
- Coenzymes
- Nucleotide Triphosphates provide energy (e.g., ATP, GTP) and participate in enzymatic phosphorylation.

Summary (Page 49)

Provides a summary of the key concepts presented in the lecture.

To-Do List (Page 50)

Tasks for students to complete before the next lecture.
- Review DNA structures.
- Define key terms.
- Draw diagrams and other illustrations.

Before Next Week's Lecture (Page 51)

For next lecture: read relevant textbook pages for information on chromosome structure.

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Description

Test your knowledge on the fundamental aspects of DNA, including its nucleotide composition, structure, and bonding. This quiz covers key contributions from scientists like Chargaff, Watson, and Crick, as well as essential concepts such as base pairing and the importance of antiparallel strands.