DNA and Structure

Question 1

What is DNA?

Answer 1

• Stands for Deoxyribonucleic Acid.
• A double-stranded helical polymer of nucleotides.

• Carries genetic instructions for protein synthesis and inheritance.

• Found in the nucleus of eukaryotic cells and cytoplasm of prokaryotes.

Question 2

Why is DNA considered the blueprint of life?

Answer 2

• Contains genes, which code for proteins.
• Controls growth, development, and function of organisms.
• Directs protein synthesis through transcription and translation.

Question 3

What are the building blocks of DNA?

Answer 3

• Nucleotides, composed of:
o A phosphate group.
o A pentose sugar (deoxyribose).
o A nitrogenous base (A, T, C, G).

Question 4

What are the four nitrogenous bases in DNA?

Answer 4

• Purines (double-ring): Adenine (A), Guanine (G).
• Pyrimidines (single-ring): Cytosine (C), Thymine (T).

Question 5

How do bases pair in DNA?

Answer 5

• Adenine (A) bonds with Thymine (T) → 2 hydrogen bonds.
• Guanine (G) bonds with Cytosine (C) → 3 hydrogen bonds.

Question 6

What is Chargaff’s Rule?

Answer 6

• The proportion of A = T and G = C in a DNA molecule.
• Ensures complementary base pairing for accurate replication.

Question 7

What is the sugar-phosphate backbone?

Answer 7

• Structural framework of DNA.
• Consists of alternating deoxyribose sugars & phosphate groups.

Question 8

What does “antiparallel” mean in DNA?

Answer 8

• DNA strands run in opposite directions.
• One strand runs 5’ → 3’, the other 3’ → 5’.

Question 9

What do 5’ and 3’ refer to in DNA?

Answer 9

• 5’ (five-prime): Phosphate attached to the 5th carbon of deoxyribose.

• 3’ (three-prime): Hydroxyl (-OH) attached to the 3rd carbon of deoxyribose.

• Determines directionality in replication and transcription.

Question 10

What is chromatin?

Answer 10

• Uncoiled, relaxed DNA in the nucleus.
• Wraps around histone proteins to form nucleosomes.

Question 11

What are histones?

Answer 11

• Positively charged proteins that help DNA supercoil into chromosomes.
• Form nucleosomes (DNA wrapped around 8 histones).
• Helps regulate gene expression - loosely packed DNA (EUCHROMATIN) is active, while tightly packed DNA is inactive.

Question 12

What is a nucleosome?

Answer 12

• Basic unit of DNA packaging.
• DNA wrapped around eight histone proteins.
• Looks like “beads on a string” under an electron microscope.

Question 13

What are chromosomes?

Answer 13

• Condensed DNA structures that carry genetic information.
• Humans have 46 chromosomes (23 pairs).

Question 14

What are telomeres?

Answer 14

• Protective caps at the ends of chromosomes.
• Prevent DNA degradation & fusion of chromosomes.
• Shorten with each cell division, contributing to aging.

Question 15

What is a karyotype?

Answer 15

• A visual representation of an organism’s chromosomes.
• Used to detect chromosomal abnormalities.

Question 16

What are sister chromatids?

Answer 16

• Identical copies of a chromosome post-replication.
• Joined at the centromere.

Question 17

What is nuclear DNA vs. mitochondrial DNA (mtDNA)?

Answer 17

• Nuclear DNA: Found in the nucleus, inherited from both parents.
• Mitochondrial DNA (mtDNA): Found in mitochondria, inherited only from the mother.

Question 18

How does mitochondrial DNA support the theory of endosymbiosis?

Answer 18

• Mitochondria have circular DNA, like bacteria.
• Suggests mitochondria evolved from free-living prokaryotic cells.

Question 19

What are plasmids?

Answer 19

• Small, circular DNA molecules separate from chromosomal DNA.
• Found in bacteria, often carry genes for antibiotic resistance.

Question 20

How does prokaryotic DNA differ from eukaryotic DNA?

Answer 20

• Prokaryotic DNA: Circular, in the nucleoid region, lacks histones.
• Eukaryotic DNA: Linear, stored in the nucleus, associated with histones.

Question 21

What is DNA replication?

Answer 21

• The process of copying DNA before cell division.
• Ensures genetic continuity.

Question 22

What is semi-conservative replication?

Answer 22

• Each new DNA molecule contains:
o One original strand (template).
o One newly synthesized strand.

Question 23

What is the role of helicase in DNA replication?

Answer 23

• Unwinds and unzips DNA by breaking hydrogen bonds.

Question 24

What is the role of DNA polymerase?

Answer 24

• Adds nucleotides to the growing strand in a 5’ → 3’ direction.
• Proofreads and fixes errors.

Question 25

What are Okazaki Fragments?

Answer 25

• Short DNA segments synthesized on the lagging strand during DNA replication. • DNA polymerase can only add nucleotides in the 5' → 3' direction, causing discontinuous synthesis. • Primase lays down an RNA primer, allowing polymerase to extend fragments. • DNA ligase joins Okazaki fragments to form a continuous strand.

Question 26

What is the function of primase?

Answer 26

• Synthesizes RNA primers for DNA polymerase to initiate replication.

Question 27

What is the difference between leading and lagging strands?

Answer 27

• Leading strand: Synthesized continuously in a 5' → 3' direction. • Lagging strand: Synthesized discontinuously in Okazaki fragments.

Question 28

What is a gene?

Answer 28

• A segment of DNA that codes for a specific protein or RNA molecule.

Question 29

How does DNA store genetic information?

Answer 29

• Through the sequence of nitrogenous bases. • Each sequence forms genes, which dictate protein production.

Question 30

What is the function of non-coding DNA?

Answer 30

• Regulates gene expression (e.g., promoters, enhancers). • Some code for tRNA, rRNA, and microRNA.

Question 31

What are Sister Chromatids and How Do They Relate to Semi-Conservative Replication?

Answer 31

• Sister chromatids are identical copies of a chromosome formed after DNA replication. • They are held together by a centromere until separated during cell division. • Semi-conservative replication ensures each chromatid contains one original DNA strand and one newly synthesized strand. • This guarantees genetic continuity between parent and daughter cells.

Question 32

What are the Stages of DNA Replication?

Answer 32

1. Initiation • Helicase unwinds the DNA double helix, breaking hydrogen bonds. • Single-stranded binding proteins (SSBs) stabilize the unwound strands. • Primase adds RNA primers to initiate replication. 2. Elongation • DNA polymerase adds complementary nucleotides in the 5' → 3' direction. • The leading strand is synthesized continuously. • The lagging strand is synthesized discontinuously as Okazaki fragments. 3. Termination • Exonuclease removes RNA primers, replacing them with DNA. • DNA ligase seals gaps between Okazaki fragments. • The two identical DNA molecules coil into sister chromatids.

Question 33

What are the Functions of DNA?

Answer 33

• Genetic Blueprint: Stores hereditary information. • Replication: Ensures genetic continuity in cell division. • Protein Synthesis: Provides instructions for mRNA transcription and protein translation. • Cell Function Regulation: Controls gene expression via non-coding DNA and regulatory sequences.

Question 34

How Do Different Species on Earth Differ in Their DNA?

Answer 34

• Chromosome Number: Varies among species (humans = 46, dogs = 78, fruit flies = 8). • Base Sequence Differences: Unique genetic codes define species-specific traits. • Genome Size: Some species have larger or smaller genomes (e.g., humans ≈ 3 billion base pairs, E. coli ≈ 4.6 million). • Gene Variation: Differences in gene number and gene expression lead to diverse biological features.

Question 35

What is the difference between introns and exons?

Answer 35

- Exons: coding sequences that remain in mRNA and are translated into proteins. - Introns: non-coding sequences that are removed during RNA splicing. - Non- Coding DNA: includes promotes, enhances, and introns.

Question 36

Chìa khóa để mở khóa tiềm năng của bạn là gì?

Answer 36

"Càng học nhiều, bạn càng khám phá ra những khả năng vô tận bên trong mình."