Molecular Biology: DNA Structures and Functions

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Questions and Answers

What is the approximate helical length of B-DNA?

4.5 nm

2.5 nm

3.4 nm (correct)

5.0 nm

Which form of DNA is left-handed?

A-DNA

B-DNA

Z-DNA (correct)

None of the above

What is the process called when double-stranded DNA separates into single strands at high temperatures?

Melting (correct)

Transcription

Replication

Renaturation

Which form of DNA has the widest major groove?

B-DNA (D) Signup and view all the answers

What is the approximate base-pair spacing in A-DNA?

0.26 nm (B) Signup and view all the answers

What is the temperature at which half of the DNA in a solution is denatured called?

Melting Temperature (Tm) (B) Signup and view all the answers

What happens to denatured DNA if the denaturing conditions are removed?

It renatures to form the duplex structure. (B) Signup and view all the answers

Which of the following factors can influence the denaturation of DNA?

All of the above (D) Signup and view all the answers

Which of the following conditions can denature DNA?

High temperature (A), Extreme pH (B), Dilute salt solutions (C) Signup and view all the answers

Which form of DNA has the shortest helical length?

A-DNA (C) Signup and view all the answers

What is the main function of DNA in living organisms?

Encoding genetic information (C) Signup and view all the answers

Which of these is NOT a characteristic of Z-DNA?

Wide and deep major groove (C) Signup and view all the answers

Which of the following is the process where DNA is copied into RNA?

Transcription (C) Signup and view all the answers

Which form of DNA is considered the most common form found in cells?

B-DNA (D) Signup and view all the answers

How does DNA replicate itself?

Semi-conservatively, with each new strand containing one original and one newly synthesized strand (B) Signup and view all the answers

What is the compact structure that a cell's DNA is condensed into called?

Chromosome (C) Signup and view all the answers

What is the approximate diameter of A-DNA?

2.6 nm (D) Signup and view all the answers

What is the significance of the directionality (5' to 3') in nucleic acids?

It determines the order of nucleotide bases in the sequence. (D) Signup and view all the answers

What are the primary proteins that DNA associates with in chromatin?

Histones (C) Signup and view all the answers

What is the term for the unit of DNA wrapped around histones?

Nucleosome (B) Signup and view all the answers

What is the chemical bond that links nucleotides together in a nucleic acid chain?

Phosphodiester bond (A) Signup and view all the answers

Which of the following statements accurately describes Chargaff's rule?

The amount of adenine (A) is equal to the amount of thymine (T), and the amount of guanine (G) is equal to the amount of cytosine (C). (A) Signup and view all the answers

Which of the following statements about the secondary structure of DNA is TRUE?

It involves interactions between two DNA chains. (D) Signup and view all the answers

Which of the following scientists proposed the 3D structure of DNA?

James Watson and Francis Crick (A) Signup and view all the answers

What is the role of nucleoside triphosphates (NTPs) in nucleic acid synthesis?

They provide energy for the polymerization of nucleotides. (B) Signup and view all the answers

What is the difference in the primary structure of DNA and RNA?

DNA contains thymine (T), while RNA contains uracil (U). (A), DNA is a polymer of deoxyribose nucleotides, while RNA is a polymer of ribose nucleotides. (B) Signup and view all the answers

What is the term for the helical structure of DNA?

Secondary Structure (C) Signup and view all the answers

Which direction does the double helix twist in DNA?

Right-handed (A) Signup and view all the answers

What is the principle behind the antiparallel orientation of DNA strands?

One strand runs in a 5' to 3' direction while the other runs in a 3' to 5' direction. (C) Signup and view all the answers

What is the type of bonding that stabilizes base pairing in DNA?

Hydrogen Bonding (D) Signup and view all the answers

What is the reason for the formation of major and minor grooves in the DNA double helix?

The double helix is not perfectly symmetric. (C) Signup and view all the answers

What components of DNA are found in the backbone of the helix?

Deoxyribose Sugar and Phosphate Groups (C) Signup and view all the answers

Where are the hydrophobic base pairs positioned within the DNA double helix?

Stacked internally within the helix (B) Signup and view all the answers

What is the primary function of the major and minor grooves in the DNA double helix?

Allowing for protein binding and DNA regulation (D) Signup and view all the answers

What is the significance of the complementary base pairing found in DNA?

It allows for the accurate copying of DNA during replication. (A) Signup and view all the answers

What are the non-coding sequences that interrupt eukaryotic genes called?

Introns (A) Signup and view all the answers

Which of the following accurately describes messenger RNA (mRNA)?

It serves as a template for protein synthesis. (B) Signup and view all the answers

How many exons does the gene for ovalbumin contain?

8 (A) Signup and view all the answers

What is the role of ribosomal RNA (rRNA) in the cell?

To form the ribosome structure for protein synthesis. (A) Signup and view all the answers

Which of the following structures is formed when single-stranded RNA folds back through complementary base pairing?

Secondary structures (C) Signup and view all the answers

Signup and view all the answers

Study Notes

Primary Structure of DNA/RNA

Nucleic acids are linear sequences of nucleotides linked by phosphodiester bonds.
Phosphodiester bonds bridge the 3' and 5' positions of the sugar moiety.
Directionality runs from 5' to 3'.
Oligonucleotides/polynucleotides are short/long chains of nucleotides.
The backbone consists of phosphate and pentose sugar.
Nucleotide monophosphates (NMPs) are basic building blocks of nucleic acids while nucleoside triphosphates (NTPs) are the activated precursors for synthesis.
Example DNA sequence: 5'-ATGCGGCTATTGTA-3'
Example RNA sequence: 5'-UGCGGCUAUUGUA-3'

Secondary Structure of DNA

Erwin Chargaff's findings:
- Base composition varies between species.
- Base composition is consistent within a species, regardless of tissue or environment.
- The number of adenine residues equals the number of thymine residues (A=T).
- The number of guanine residues equals the number of cytosine residues (G=C).
- The sum of purines (A+G) equals the sum of pyrimidines (T+C).
Right-handed double helix.
Two helical DNA chains wound around a common axis.
Antiparallel orientation: Chains run in opposite directions (5' to 3' and 3' to 5').
Base-pairing via hydrogen bonds (A-T = 2 bonds, G-C = 3 bonds).
Hydrophilic sugar-phosphate backbone on the outside.
Hydrophobic bases stacked inside.
Major and minor grooves on the DNA surface due to the offset pairing of the strands.

DNA Denaturation and Renaturation

DNA's secondary structure is sensitive to pH, temperature and ionic strength (salt).
Denaturation: separation of DNA strands due to high temperature or other factors.
Melting temperature (Tm): temperature at which half of the DNA in a solution is denatured.
Renaturation: reformation of the double helix structure under favorable conditions (cooling, neutralization of pH, or dilution of denaturants).

DNA Replication

DNA replicates in a semi-conservative way.
Pre-existing parent strands separate. Each strand acts as a template for the biosynthesis of a new complementary strand.

Roles of DNA

Encodes genetic information for cell growth, function, and reproduction.
The amino acid sequence of proteins and nucleotide sequences of RNA are specified by the DNA sequence.
Double-stranded helix structure with an internal structure.

DNA Size/Organization

A cell's DNA is condensed into chromosomes to fit inside the cell.
Chromatin: fibers of proteins (histones) and DNA which make up the chromosome.
Histones (proteins) tightly associate with DNA, forming nucleosomes.
Non-histone proteins assist in chromosome structure or regulate gene expression.

Gene

A segment of DNA that codes for a protein or RNA.
Prokaryotic genes are often continuous, while eukaryotic genes have introns (non-coding sequences) and exons (coding sequences). Exons, expressed regions, are the coding areas of a gene.
Example: Genes for ovalbumin and β hemoglobin subunit have exons and introns.

Types of RNA

Messenger RNA (mRNA): Carries genetic code from DNA to ribosomes for protein synthesis.
Transfer RNA (tRNA): Carries amino acids to ribosomes, matching them to mRNA codons.
Ribosomal RNA (rRNA): Part of the ribosome, the protein synthesis machinery.

Secondary Structures of RNA

Single-stranded RNA folds back through complementary base pairing.
Common secondary structures include stems (stem-loops), loops, bulges, and junctions.
Example: tRNA has specific secondary structures critical for its function.
Example: rRNA has complex secondary structures needed during protein synthesis.

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Description

Test your knowledge on the various forms of DNA and their characteristics with this quiz. It covers essential concepts such as helical length, denaturation, and DNA replication. Perfect for students studying molecular biology!