Central Dogma and Key Experiments in Biology

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Questions and Answers

What role does DNA polymerase play in proofreading?

It corrects errors in newly synthesized DNA. (correct)

It initiates the transcription process.

It synthesizes new DNA strands.

It removes damaged DNA segments.

What type of mutation is primarily caused by ultraviolet (UV) light?

Thymine dimers (correct)

Translocations

Insertions

Point mutations

During RNA transcription, which direction does RNA polymerase read the template DNA strand?

3'→5' (correct)

5'→5'

3'→3'

5'→3'

What is the function of a gene's promoter?

To bind RNA polymerase and help initiate transcription. Signup and view all the answers

Which of the following best defines the concept of 'homozygous'?

Having two identical alleles for a gene. Signup and view all the answers

What is the FIRST step in the PCR process?

Denaturation Signup and view all the answers

Which statement best describes the function of transfer RNA (tRNA)?

It carries amino acids to the ribosome for protein synthesis. Signup and view all the answers

What is a codon?

A sequence of three nucleotides that encodes an amino acid. Signup and view all the answers

What is the primary purpose of the dideoxyribonucleotide triphosphates (ddNTPs) in DNA sequencing?

To selectively terminate DNA strand elongation. Signup and view all the answers

What type of genetic marker are Short Tandem Repeats (STRs) considered?

Microsatellite markers. Signup and view all the answers

What is the correct sequence of information flow in cells?

DNA→RNA→protein Signup and view all the answers

What is the significance of the Griffith Experiment?

It demonstrated bacterial transformation. Signup and view all the answers

What role did Avery, MacLeod & McCarty's experiment play in the understanding of heredity?

It confirmed DNA as the hereditary material. Signup and view all the answers

Which of the following describes Chargaff's Rules?

A=T and G≠C Signup and view all the answers

What was a key contribution of Rosalind Franklin to the study of DNA?

Providing the X-ray diffraction image known as Photo 51. Signup and view all the answers

What direction does DNA polymerase synthesize the daughter DNA strand?

5'→3' Signup and view all the answers

Which model of DNA replication is demonstrated by the Meselson & Stahl Experiment?

Semiconservative model Signup and view all the answers

What is the primary function of the enzyme helicase in DNA replication?

To unwind the DNA double helix. Signup and view all the answers

What is true about the lagging strand during DNA replication?

It is synthesized in fragments known as Okazaki fragments. Signup and view all the answers

Which statement accurately differentiates DNA polymerase III and DNA polymerase I in E.coli?

DNA polymerase III primarily synthesizes DNA, while DNA polymerase I has a proofreading function. Signup and view all the answers

Study Notes

Central Dogma of Molecular Biology

Information flows from DNA to RNA to protein
This is the fundamental principle of molecular biology

Friedrich Miescher

Discovered nuclein (later identified as DNA)

Fred Griffith Experiment (1928)

Used Streptococcus pneumoniae bacteria (rough and smooth strains)
Demonstrated transformation, where non-virulent bacteria became virulent
Identified a "transforming agent" a substance that caused the change

Transforming Agent

The substance responsible for transformation in Griffith's experiment, later identified as DNA

Avery, MacLeod & McCarty Experiment (1944)

Confirmed DNA as the transforming agent, not protein
Used enzymes to degrade different components of the bacteria extract and tested their transforming ability

Hershey & Chase Experiment (1952)

Used bacteriophages (virus that infects bacteria)
Demonstrated that DNA, not protein, enters bacterial cells during infection. This is a crucial piece of evidence supporting DNA being the genetic material.

Chargaff’s Rules

DNA composition varies by species.
A=T, and G=C

Rosalind Franklin

X-ray diffraction photographs (such as Photo 51) provided crucial structural information about DNA

Watson & Crick (1953)

Determined the double helix structure of DNA

DNA Structure

Bases pair A-T and G-C
DNA has 5' and 3' ends

DNA Replication

Occurs during the S phase of the cell cycle

Models of DNA Replication

Conservative, Semiconservative and Dispersive

Meselson & Stahl Experiment (1958)

Used isotopes of nitrogen to demonstrate semiconservative replication

DNA Replication Process

Origin of replication: replication begins
Replication bubble: region of DNA unwinding.
Replication forks: Y-shaped regions where DNA is unwound and replicated.
Direction of DNA synthesis: 5' → 3' (New DNA strand is built in this direction)

Enzymes in DNA Replication

DNA polymerase: replicates DNA
Deoxyribonucleotide triphosphates (dNTPs): building blocks for DNA synthesis
Topoisomerase: relieves DNA supercoiling
Helicase: unwinds DNA
Single-strand binding proteins (SSBPs): stabilize single-stranded DNA
Primase: synthesizes RNA primers
DNA polymerase III: main replication enzyme
DNA polymerase I: replaces RNA primers with DNA
Ligase: joins Okazaki fragments

Leading and Lagging Strands

Leading strand: synthesized continuously
Lagging strand: synthesized in Okazaki fragments (short segments)

DNA Repair

Proofreading: DNA polymerase corrects mistakes during replication
Mismatch repair: corrects base pair mismatches and gaps.
Nucleotide excision repair: Repairs bulky DNA damage from radiation
Mutagens: agents that cause mutations
Thymine dimers: type of DNA damage

Gene Expression

Gene: segment of DNA that codes for a protein
Allele: variant form of a gene
Phenotype: observable characteristics
Genotype: genetic makeup
Dominant trait: expressed even if only one copy is present
Recessive trait: expressed only if two copies are present
Homozygous: having two identical alleles
Heterozygous: having two different alleles
Transcription: DNA to mRNA process
Messenger RNA (mRNA): carries genetic information from DNA to ribosomes
Codon: 3-nucleotide sequence on mRNA
RNA polymerase: synthesizes RNA using DNA as a template
Promoter: region of DNA that initiates transcription
Transcription factors: proteins that regulate transcription (in eukaryotes only)
Exons: coding regions of a eukaryotic gene
Introns: non-coding regions of a eukaryotic gene
Pre-mRNA: initial mRNA transcript in eukaryotes
RNA processing: modification of pre-mRNA in eukaryotes
Genetic code: set of rules that dictates how codons are translated into amino acids
Start codon (AUG): initiates translation
Stop codons (UAA, UAG, UGA): terminate translation

Translation

Translation: mRNA to protein process
Ribosome: site of protein synthesis
Transfer RNA (tRNA): carries amino acids to ribosomes
Anticodon: sequence on tRNA that complements codon on mRNA
Amino acid attachment site: site on tRNA where the amino acid is attached
A, P, and E sites: ribosomal sites involved in translation.

DNA Technology

Gel electrophoresis: separates DNA fragments based on size
Polymerase Chain Reaction (PCR): amplifies DNA sequences
DNA sequencing: determines the order of nucleotides in DNA
Automated DNA sequencing: utilizes fluorescently labeled nucleotides for fast sequencing.
Human Genome Project: mapped the entire human genome.

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Description

Explore the foundational aspects of molecular biology through the central dogma and significant experiments by researchers like Griffith, Avery, and Hershey & Chase. This quiz covers the flow of genetic information and the pivotal discoveries that shaped our understanding of DNA's role. Test your knowledge of these critical milestones in biological science.