Molecular Biology vs. Genetics

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Questions and Answers

What distinguishes molecular biology from transmission genetics?

It ignores the role of enzymes

It studies genes at a molecular level (correct)

It solely focuses on visible traits

It includes ecological interactions

Which scientist is credited with providing evidence for the chromosome theory of inheritance?

Thomas Hunt Morgan (correct)

Gregor Johann Mendel

Friedrich Miescher

Barbara McClintock

What was the key finding of Beadle and Tatum's research?

Friedrich Miescher first discovered nuclein

Each gene encodes a single enzyme (correct)

Recombination can occur in all organisms

Chromosomes contain multiple genes

What contribution did Barbara McClintock and Harriet Creighton make to molecular biology?

Demonstrated chromosome recombination Signup and view all the answers

Which organism did Thomas Hunt Morgan use to study genetics?

Fruit flies Signup and view all the answers

Who first isolated nuclein and identified its components?

Friedrich Miescher Signup and view all the answers

What hypothesis did Sir Archibald Garrod propose related to genes?

Genes are connected to enzymes Signup and view all the answers

What is the primary function of the Rho protein in rho-dependent termination?

To unwind the RNA-DNA hybrid and facilitate transcription termination. Signup and view all the answers

Which characteristic is essential for the rut site where the Rho protein binds?

It should be rich in cytosines and lack secondary structure. Signup and view all the answers

What role does the palindromic GC-rich region play in rho-independent termination?

It forms a stable hairpin structure that destabilizes the transcription complex. Signup and view all the answers

What is the reason for the weak RNA-DNA hybrid formed by the A-U base pairing during rho-independent termination?

A-U base pairs only have two hydrogen bonds compared to G-C pairs. Signup and view all the answers

What occurs immediately after Rho catches up to the paused RNA polymerase during transcription?

Rho unwinds the RNA-DNA hybrid within the transcription bubble. Signup and view all the answers

What is the role of foreign DNA in phage vectors?

It replaces removed phage genes for packaging. Signup and view all the answers

What limits the size of foreign DNA that can be inserted into phage vectors?

The length of the phage head. Signup and view all the answers

What method yields two arms and two stuffer fragments in the construction of phage vectors?

Digestion with EcoR1 to form cos sites. Signup and view all the answers

How do cosmids function in the context of DNA cloning?

As hybrids that can replicate like plasmids and be packaged like phages. Signup and view all the answers

What is a distinct feature of clones using phage vectors compared to traditional bacterial transformations?

Clones form plaques rather than colonies. Signup and view all the answers

What is the maximum size of DNA fragments that cosmids can typically carry?

40-50 kb. Signup and view all the answers

Which characteristic of phage vectors allows for more efficient infection of cells compared to plasmids?

Natural ability to transduce bacterial DNA. Signup and view all the answers

What happens to the arms during the construction of phage vectors?

They cannot religate due to insufficient DNA. Signup and view all the answers

Which two components are primarily involved in the ligation step of phage vector construction?

Vector head and tail. Signup and view all the answers

What is the significance of the 5'-overhanging single-stranded ends produced by EcoRI?

They provide a means for base pairing with complementary strands. Signup and view all the answers

How are restriction endonucleases best described in their function?

They cut DNA at specific sites to create precise fragments. Signup and view all the answers

What does the 'G' in the recognition sequence GAATTC represent regarding EcoRI's cleavage?

It is the nucleotide where EcoRI cuts both strands. Signup and view all the answers

What type of ends do restriction endonucleases like BamHI create when they cleave DNA?

5' overhangs Signup and view all the answers

Which enzyme is used as an example of a restriction endonuclease that produces blunt ends?

SmaI Signup and view all the answers

What is indicated by the suffix in 'Hind III' when referring to restriction enzymes?

The number of times it has been isolated. Signup and view all the answers

Which of the following best describes a DNA molecule with blunt ends?

Ends that are not capable of base pairing. Signup and view all the answers

What is a principal role of Taq polymerase in recombinant DNA technology?

It creates complementary strands through amplification. Signup and view all the answers

Why are cohesive ends important in the context of recombinant DNA technology?

They allow for the effective joining of DNA fragments. Signup and view all the answers

What is the main function of reverse transcriptase in the context of a retrovirus?

It helps in the integration of DNA into the host genome. Signup and view all the answers

Which statement accurately describes the role of the Ac and Ds elements in maize kernel color variation?

Ds transposes into the C gene, mutating it before transposing out. Signup and view all the answers

How can mobile genetic elements like transposons contribute to evolution?

They can facilitate the fusion of different genome segments. Signup and view all the answers

Why is it said that transposable elements may be a key mechanism in creating genomic changes?

Their integration has the potential to alter gene functions significantly. Signup and view all the answers

What is the key difference between autonomous and non-autonomous transposons?

Autonomous transposons can transpose without any assistance. Signup and view all the answers

What does the term 'provirus' refer to in the context of retroviruses?

It is the integrated DNA copy of the retrovirus within the host genome. Signup and view all the answers

What is the function of the Ds element in relation to the C locus in maize?

Ds causes mutations by integrating into the C gene. Signup and view all the answers

In the context of transposons, what is meant by 'joining unlinked segments of host genome'?

Transposons can facilitate the creation of gene fusion events. Signup and view all the answers

What role does the enzyme reverse transcriptase play in the lifecycle of a retrovirus?

It creates a DNA copy of the viral RNA. Signup and view all the answers

Which of the following statements is true regarding mobile genetic elements?

They have the potential to provide new functions through integration in the genome. Signup and view all the answers

Study Notes

Chapter 1 History

Molecular Biology is the study of gene structure and function at the molecular level
It encompasses genetics and biochemistry disciplines
Early knowledge on the molecular nature of genes was absent so it was known as transmission genetics
Gregor Johann Mendel studied transmission genetics using pea plants
Chromosomes were recognized as units carrying genes within the nucleus
In 1910, Thomas Hunt Morgan studied Drosophila melanogaster to provide evidence for the chromosome theory of inheritance. This was simpler than working with plants
Barbara McClintock and Harriet Creighton (1931) demonstrated recombination between easily identifiable features, establishing a chromosome-gene relationship

Early Foundations

Friedrich Miescher (1869) discovered nuclein (DNA) in white blood cells, noting its phosphorus content
Phoebus Levene (1909–1929) identified the DNA components: sugar (deoxyribose), phosphate group, and four nitrogenous bases (adenine, thymine, cytosine, guanine). He incorrectly proposed a simple tetranucleotide structure.
Oswald Avery, Colin MacLeod, and Maclyn McCarty (1944) showed that DNA, not protein, carries genetic information through transformation experiments.

Structural Studies of DNA

Erwin Chargaff (1950) established the crucial rule that the amount of adenine equals thymine, and cytosine equals guanine in DNA. This aided a better understanding of DNA.
Maurice Wilkins and Rosalind Franklin (1951-1953) used X-ray diffraction techniques to study the structure of DNA. Franklin's work, especially Photo 51, provided key data on DNA's helical structure and dimensions

Watson & Crick

Chargaff's rules and Franklin's X-ray diffraction data guided Watson and Crick (1953) to propose the double-helical model for DNA structure.
Their model showed two strands running in opposite directions, held together by A-T and C-G base pairs.

Chapter 2 DNA Nucleosome

DNA is organized into giant molecules called chromosomes
Each chromosome contains a single DNA molecule, housing multiple genes
Each gene specifies the instructions to make a single protein. In humans each chromosome contains approximately 2000 genes and 46,000 genes.
Chromatin fibers & chromosomes are two types of DNA that differ in condensation levels at different stages. Chromosomes are the tightly condensed form of DNA within the cell's nucleus.

Chromosomes and Chromatin: Higher Levels of Chromatin Structure

The lowest level is the 10 nm nucleosome core (DNA wrapped around histone proteins).
The next level is the 30-nm fiber (compacted nucleosomes).
The next level is the 300-nm fiber, and finally chromosome structures (700-1400nm).
Different levels of compaction allow chromosomes to fit within the cell's nucleus.
Structural proteins and DNA-packing regulate gene expressing.

Chromatin

Euchromatin is less condensed, actively expressed regions (lighter stained) - ~92% of DNA
Heterochromatin is more condensed, less active regions (darker stained), contains fewer genes

Mosaisim

Adult females are genetic mosaics because different cells will have inactivated X-chromosomes (Barr bodies) based on their parental origin. The calico-cat's fur colour is a good example.
X-inactivation is important for preventing the excessive expression of gene transcripts (more commonly occurring in females).

Chapter 3 Vectors and oligonucleotides

Restriction enzymes are endonucleases cutting DNA within specific sequences.
Restriction enzymes are used to cut DNA at specific locations.
Experiment Using Restriction Endonuclease: Restriction enzymes are used by Boyer and Cohen to create recombinant DNA vectors by ligating 2 separate DNA pieces together
Restriction modification system • A group of enzymes prevent the host cells from being destroyed by their own restriction enzymes.
DNA mapping is a practice used by scientists to locate genes in DNA
Plasmid vectors –pBR 322 and pUC vectors • pBR 322 is a widely used E. coli cloning vector. • pUC is a more widely used plasmid vector.

Plasmids, Cosmids, M13 Phage vectors

Plasmids are small, circular DNA molecules that replicate separately from the chromosome.
Cosmids are hybrid plasmids, that contain cos sequences of bacteriophage lambda
M13 Phage and its vectors are DNA from bacteriophage M13. These sequences are useful for site-directed mutagenesis studies and for sequencing processes

Chapter 4 Techniques in Molecular Biology

Polymerase Chain Reaction (PCR) is a technique for creating multiple copies of a DNA fragment.
RT-PCR (reverse transcriptase PCR) is a variation of PCR used to amplify only certain areas of DNA or RNA
Real-Time PCR (quantitative PCR) is a technique for determining the amount of DNA or RNA, which is monitored in real time as it is being measured.
Gel Electrophoresis is used to separate DNA or RNA fragments based on their size and charge.
Other techniques like Southern Blotting, Northern blotting and Western blotting are used in identifying specific DNA or RNA sequences using tagged probes or antibodies.

Chapter 5 Transgenesis

Transgenesis is the technique of introducing foreign genetic material into an organism allowing the organism to express new genetic traits.
There are different methods of introducing new DNA into cells (physical & chemical).
Physical methods include microinjection, biolistic, electroporation.
Chemical methods include lipids, liposomes mediated, non-liposomal.
Biological methods include conjugation, transformation, transduction, Agrobacterium mediated transfer.

Chapter 6 Recombinational Repair

Homologous recombination occurs during meiosis.
The process of homologous recombination allows for shuffling of genes among maternal and paternal chromosomes, generating diverse genetic combinations in offspring.
Holliday model describes how homologous recombination occurs as a way of repairing DNA.

Chapter 7 Mobile Genetic Elements

Transposable Elements (TEs) are DNA segments capable of moving from one genomic position to another
TE's are significant features in diverse evolutionary processes and shaping the genome
McClintock discovered elements Ac and Ds and described transposable elements
Mechanisms of transposition include cut and paste & replicative transposition
Transposable elements are involved in various cellular processes

Chapter 8 Regulation of Gene Activity

Prokaryotes have operons, groups of genes transcribed together.
The lac operon regulates lactose metabolism.
Negative control: repressor proteins prevent transcription when a substrate is absent.
Positive control: activator proteins enhance transcription when a substrate is present (example, cAMP and CAP controlling transcription).
The trp operon regulates tryptophan production. It uses attenuation to regulate transcription, depending on substrate tryptophan, to ensure correct regulation.
The ara operon is regulated by the presence of arabinose in the cell. The protein AraC controls this operon.

Chapter 9

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Chapter 10

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Test your knowledge on the key concepts that differentiate molecular biology from transmission genetics. This quiz covers important discoveries and contributions from notable scientists in the field of genetics. Challenge yourself with questions about chromosome theory, gene function, and classic experiments in molecular biology.