Nucleic Acids-DNA and RNA

Question 1

DNA Structure

Answer 1

Double helix structure, made of two strands

Located in the nucleus (in eukaryotes)
Stores genetic information for cellular function and reproduction

Contains deoxyribose sugar in each nucleotide

Provides a permanent genetic code for cells and organisms

Question 2

RNA Structure

Answer 2

Single-stranded molecule
Functions mostly outside the nucleus in eukaryotes (e.g., cytoplasm)

Transfers genetic information for protein synthesis

Contains ribose sugar in each nucleotide

Does not provide a permanent code, except in RNA viruses

Question 3

Nucleotide Structure

Answer 3

Each nucleotide consists of a phosphate group, sugar (ribose or deoxyribose), and a nitrogenous base

Nucleotides are monomers for polymers like DNA and RNA

DNA nucleotides contain deoxyribose; RNA nucleotides contain ribose

Question 4

Nitrogenous Bases

Answer 4

Purines (2 rings): Adenine (A), Guanine (G)

Pyrimidines (1 ring): Cytosine (C), Thymine (T, in DNA), Uracil (U, in RNA)

Question 5

Nitrogenous Base Pairing

Answer 5

DNA: Adenine pairs with Thymine (A-T), and Cytosine pairs with Guanine (C-G)

RNA: Adenine pairs with Uracil (A-U), and Cytosine pairs with Guanine (C-G)

Question 6

Pentose Sugar in DNA & RNA

Answer 6

Deoxyribose (DNA): Lacks an OH group on Carbon 2 (only H present)

Ribose (RNA): Has an OH group on Carbon 2

Carbon 1: Binds with the nitrogenous base
Carbon 3: Always OH
Carbon 5: Binds with the phosphate group

Question 7

Phosphate Group

Answer 7

The phosphate group has a negative charge that makes DNA and RNA molecules negatively charged

Binds to Carbon 5 of the sugar, linking to the next nucleotide’s Carbon 3 through phosphodiester bonds

Forms the sugar-phosphate backbone of DNA and RNA, providing structural stability

Question 8

Complementary Base Pairing

Answer 8

Bases pair with hydrogen bonds:
A-T in DNA with 2 hydrogen bonds
C-G in both DNA and RNA with 3 hydrogen bonds

This base pairing stabilizes the DNA double helix structure and enables accurate replication

Question 9

Antiparallel Arrangement

Answer 9

DNA strands run in opposite directions:
One strand runs 5’ to 3’
The other strand runs 3’ to 5’

This arrangement is essential for DNA replication and stability

Question 10

Chargaff’s Rule

Answer 10

In DNA, % of Adenine (A) = % of Thymine (T) and % of Guanine (G) = % of Cytosine (C)

A-T and C-G base pairing explains this rule, crucial for DNA structure and replication

Question 11

Hershey-Chase Experiment

Answer 11

Proved DNA is the genetic material

Used bacteriophages (viruses) with DNA labeled with radioactive phosphorus (³²P) and protein labeled with radioactive sulfur (³⁵S)