dna & genom

Question 1

What are the components of a nucleotide?

Answer 1

Pentose Sugar (5 carbons), Phosphate Group, Nitrogenous base attached to carbon 1

Nucleotides are the building blocks of nucleic acids like DNA and RNA.

Question 2

Define nucleoside.

Answer 2

Pentose sugar + nitrogenous base

Nucleosides do not contain a phosphate group.

Question 3

What is the difference between a nucleoside and a nucleotide?

Answer 3

Nucleoside + phosphate = nucleotide

Nucleotides are essential for the formation of DNA and RNA.

Question 4

What forms the sugar-phosphate backbone in polynucleotides?

Answer 4

Phosphodiester bonds between nucleotides

This backbone is crucial for the structural integrity of nucleic acids.

Question 5

Describe the structure of DNA.

Answer 5

Double helix, phosphodiester bonds, complementary base pairing, hydrogen bonds, antiparallel orientation

DNA’s structure is key to its function in genetics.

Question 6

What evidence supports the antiparallel strands of DNA?

Answer 6

One strand runs 5’ to 3’ while the other runs 3’ to 5’

This orientation is critical for DNA replication and function.

Question 7

What is the structure of RNA?

Answer 7

Polyribonucleotide, same phosphodiester bond, uracil instead of thymine, usually single-stranded

RNA plays several roles in gene expression and regulation.

Question 8

How does the organization of DNA differ in prokaryotes and eukaryotes?

Answer 8

Eukaryotic genome: larger, multiple, linear, found in nucleus; Prokaryotic genome: smaller, single, circular, found in nucleoid

This structural difference impacts gene regulation and expression.

Question 9

What evidence supports semi-conservative DNA replication?

Answer 9

Generation 0: only heavy 15N-15N DNA; Generation 1: hybrid DNA; Generation 2: 50% hybrid, 50% light DNA

This experiment demonstrated how DNA strands are conserved during replication.

Question 10

Explain the process of DNA replication.

Answer 10

Involves polymerization of free deoxyribonucleoside triphosphates during the S phase

DNA replication is crucial for cell division and genetic continuity.

Question 11

What role does helicase play in DNA replication?

Answer 11

Binds and unzips DNA by breaking hydrogen bonds

This is essential for separating the DNA strands for replication.

Question 12

How does DNA polymerase function during replication?

Answer 12

Catalyzes formation of phosphodiester bonds linking DNA nucleotides, synthesizes in 5’ to 3’ direction

Its activity is critical for the accuracy of DNA replication.

Question 13

What are Okazaki fragments?

Answer 13

Discontinuous segments synthesized on the lagging strand

These fragments are later joined by DNA ligase.

Question 14

What is the Central Dogma of molecular biology?

Answer 14

Flow of genetic information: Replication → Transcription → Translation

This framework explains how genetic information is expressed.

Question 15

List the six key features of the genetic code.

Answer 15

• Triplet Code
• Universal Code
• Degenerate
• Non-overlapping
• Continuous
• Includes start and stop sequences

These features ensure efficient and accurate protein synthesis.

Question 16

Why is the genetic code considered a triplet code?

Answer 16

3 nucleotides allow for 64 codons, enough to encode 20 amino acids

This redundancy helps protect against mutations.

Question 17

What are the main components of a gene?

Answer 17

• Promoter
• Coding Region
• Start Codon
• Stop Codon
• Regulatory Elements
• Terminator

These components are essential for gene regulation and expression.

Question 18

Summarize the transcription process.

Answer 18

• Initiation: RNA polymerase binds to promoter
• Elongation: RNA synthesis by adding nucleotides
• Termination: Stops at terminator sequence
• Product: pre-mRNA or mRNA

Transcription is the first step in gene expression.

Question 19

What is the role of RNA polymerase in transcription?

Answer 19

Synthesizes RNA from the DNA template strand

It is the key enzyme in the transcription process.

Question 20

Describe the structure of mRNA.

Answer 20

Single-stranded, contains codons, has a 5’ cap and 3’ poly-A tail

These features enhance stability and translation efficiency.

Question 21

How does tRNA function in protein synthesis?

Answer 21

Carries specific amino acids and has anticodons that pair with mRNA codons

This ensures the correct amino acids are added to the growing polypeptide chain.

Question 22

What is the primary function of rRNA?

Answer 22

Major component of ribosomes, catalyzes protein synthesis

rRNA provides structural support in the ribosome.

Question 23

What is amino acid activation?

Answer 23

Enzyme activation, ATP hydrolysis, attachment to tRNA

This process is crucial for preparing amino acids for protein synthesis.

Question 24

What is amino acid activation?

Answer 24

Specific amino acid covalently attached to 3’ CCA stem of a specific tRNA with a specific anticodon by a specific aminoacyl-tRNA synthetase; ATP is required, resulting in aminoacyl tRNA

This process ensures that the correct amino acid is delivered for protein synthesis.

Question 25

What is the significance of amino acid activation?

Answer 25

Enzyme can achieve double specificity, where correct amino acid is attached to tRNA with corresponding anticodon ## Footnote This is crucial for accurate protein synthesis.

Question 26

Describe the process of translation initiation.

Answer 26

Translation initiation factors help bind small ribosomal subunit and initiator tRNA carrying methionine to mRNA; Anticodon of initiator tRNA base pairs with start codon (AUG); Large ribosomal subunit binds to form translational initiation complex ## Footnote This sets the stage for the elongation phase of translation.

Question 27

What happens during the elongation phase of translation?

Answer 27

A) Second aminoacyl-tRNA binds at A site; B) Peptide bond forms between adjacent amino acids; C) Ribosome translocates, shifting tRNA to Exit site ## Footnote The process continues until a stop codon is reached.

Question 28

What triggers termination in the translation process?

Answer 28

Termination occurs when stop codon (UAA/UAG/UGA) reaches A site; Release factors hydrolyse covalent bonds between polypeptide and tRNA ## Footnote This releases the polypeptide and disassembles the ribosome.

Question 29

True or False: Simultaneous transcription and translation only occur in prokaryotes.

Answer 29

True ## Footnote This is due to the absence of a nucleus in prokaryotes, allowing both processes to occur concurrently.

Question 30

Define gene mutation.

Answer 30

An alteration in the sequence of nucleotide bases in DNA of a gene, which may change the sequence of amino acids in a polypeptide chain ## Footnote Mutations can lead to various effects on protein function.

Question 31

What is a frameshift mutation?

Answer 31

Caused by insertion or deletion of nucleotides not divisible by 3, disrupts reading frame and results in non-functional polypeptide ## Footnote This alters the entire downstream sequence of amino acids.

Question 32

What is a silent mutation?

Answer 32

Point mutation with no change in amino acid sequence due to degeneracy of genetic code ## Footnote Different codons can code for the same amino acid.

Question 33

What is a missense mutation?

Answer 33

Point mutation where codon codes for a different amino acid; can be conservative or non-conservative ## Footnote This can affect protein function depending on the properties of the substituted amino acid.

Question 34

What is a nonsense mutation?

Answer 34

Point mutation that results in a premature stop codon (UAG, UAA, UGA), truncating the polypeptide ## Footnote This typically leads to a non-functional protein.

Question 35

What type of mutation occurs in the HBB gene in sickle cell anemia?

Answer 35

Point mutation (GAG → GTG) ## Footnote This mutation occurs at codon 6 of the HBB gene on chromosome 11.

Question 36

What amino acid substitution occurs due to the mutation in sickle cell anemia?

Answer 36

Glutamic acid replaced by valine ## Footnote Glutamic acid is polar, whereas valine is nonpolar.

Question 37

How does the mutation affect the solubility of hemoglobin in sickle cell anemia?

Answer 37

Hemoglobin (HbS) becomes less soluble ## Footnote This leads to polymerization under low oxygen conditions.

Question 38

What structural change occurs in red blood cells due to sickle cell anemia?

Answer 38

Red blood cells become rigid and crescent-shaped ## Footnote These are known as sickle cells.

Question 39

What are potential causes of chromosomal aberrations related to gene mutations?

Answer 39

* Replication errors * DNA repair failure * Spindle fiber issues ## Footnote Each of these can lead to breaks, misalignments, or aneuploidy.

Question 40

What are the types of structural aberrations that can result from gene mutations?

Answer 40

* Deletions * Duplications * Inversions * Translocations ## Footnote These involve changes in chromosome segments.

Question 41

What are numerical aberrations and how are they caused?

Answer 41

Nondisjunction due to gene mutations ## Footnote This can lead to extra or missing chromosomes, such as in Down syndrome (trisomy 21).

Question 42

True or False: Mutations in helicase genes can lead to chromosomal breaks.

Answer 42

True ## Footnote These replication errors can significantly impact chromosome integrity.

Question 43

Fill in the blank: The mutation in sickle cell anemia occurs at codon _______ of the HBB gene.

Answer 43

6 ## Footnote This specific location is critical for the mutation's effects on hemoglobin.