DNA Structure and Nucleic Acids

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Questions and Answers

Which nitrogenous bases are classified as purines in the primary structure of DNA?

Thymine and Cytosine

Adenine and Guanine (correct)

Cytosine and Guanine

Adenine and Thymine

What type of sugar is present in the primary structure of DNA?

Deoxyribose (correct)

Glucose

Ribose

Galactose

Which of the following is NOT a component of a deoxyribonucleotide?

Deoxyribose sugar

Phosphate group

Amino acid (correct)

Nitrogenous base

In the primary structure of DNA, what is the role of deoxyribonucleotides?

They form the genetic code. Signup and view all the answers

Which two bases pair together in the structure of DNA through hydrogen bonding?

Adenine and Thymine Signup and view all the answers

Which of the following nitrogenous bases are classified as purines?

Adenine and Guanine Signup and view all the answers

What distinguishes ribose from deoxyribose in nucleotides?

Ribose has a hydroxyl group at C2 Signup and view all the answers

What are the components of a nucleotide?

Nitrogenous base, pentose sugar, and phosphate group Signup and view all the answers

Which of the following accurately defines a nucleoside?

A nitrogenous base covalently linked to a sugar Signup and view all the answers

Which type of nitrogenous base is NOT found in DNA?

Uracil Signup and view all the answers

Which of the following best describes the structure of DNA?

Two strands forming a double helix that turn around each other Signup and view all the answers

What is the role of nucleotides with di- and triphosphates?

They act as high-energy compounds. Signup and view all the answers

Which of the following correctly outlines a function of DNA?

DNA serves as a template for RNA formation. Signup and view all the answers

What constitutes the primary structure of DNA?

Poly-deoxy-ribo-nucleotides Signup and view all the answers

Which bond is formed to connect a phosphate group to a nucleoside in a nucleotide?

Phosphoester bond Signup and view all the answers

What term describes the entire DNA content of a cell?

Genome Signup and view all the answers

How many orders of DNA structure are specifically mentioned?

Four orders Signup and view all the answers

What is the secondary structure of DNA?

Double stranded helix Signup and view all the answers

What does the 5' end of a nucleic acid strand contain?

Free phosphate group Signup and view all the answers

In which direction is the base sequence of a nucleic acid strand typically written?

5' to 3' Signup and view all the answers

Which type of bond is responsible for linking nucleotides in a nucleic acid strand?

3',5'-phosphodiester bonds Signup and view all the answers

What is present at the 3' end of a nucleic acid strand?

Free hydroxyl (OH) group Signup and view all the answers

Which of the following is a characteristic of nucleic acid strands?

They have specific 5' and 3' ends Signup and view all the answers

How are nucleotides structured within a nucleic acid strand?

They have a defined sequence written in the 5' to 3' direction Signup and view all the answers

What type of nucleic acid forms base pairs with thymine?

DNA Signup and view all the answers

Which option correctly describes the orientation of a nucleic acid strand?

5' to 3' orientation Signup and view all the answers

What bond is formed between the hydroxyl group of C3 of a nucleotide and H3PO4 attached to C5 of the pentose of the next nucleotide?

Ester bond Signup and view all the answers

Which of the following correctly describes the structure of DNA?

Double-stranded and anti-parallel Signup and view all the answers

According to Chargaff's rules, which of the following statements is accurate?

The total amount of purines equals the total amount of pyrimidines. Signup and view all the answers

What is the primary function of the major grooves in DNA?

To serve as binding sites for regulatory proteins Signup and view all the answers

What occurs during DNA denaturation?

Separation of the two strands Signup and view all the answers

What is the approximate width of a DNA double helix?

2 nm Signup and view all the answers

How many base pairs are present in each complete turn of the DNA double helix?

10 base pairs Signup and view all the answers

What is the role of the minor grooves in DNA?

Binding sites for histones Signup and view all the answers

What occurs during the annealing process of DNA?

DNA reforms a double helix structure. Signup and view all the answers

Which of the following proteins are primarily responsible for the stabilization of chromatin structure?

Histones Signup and view all the answers

What is the basic packaging unit of chromatin?

Nucleosome Signup and view all the answers

Which type of amino acids predominantly make up histones?

Basic amino acids Signup and view all the answers

What is the result of the condensation of DNA by histones?

Compaction into chromosomes Signup and view all the answers

How does DNA interact with histones?

Through ionic bonds Signup and view all the answers

Which of the following statements about nucleosomes is incorrect?

Nucleosomes are only found in prokaryotic cells. Signup and view all the answers

Which of the following proteins is not classified as a histone?

RNA polymerase Signup and view all the answers

Study Notes

DNA Structure and Types

DNA is a crucial molecule in all cells, playing a vital role in storing and transmitting genetic information.
It's present in the cell's nucleus and also in mitochondria.
DNA is a double-stranded helix, formed by millions of nucleotides.

Nucleic Acids

Nucleic acids, including DNA and RNA, are polymers of monomers called nucleotides.
Nucleotides are composed of a nitrogenous base, a pentose sugar (ribose or deoxyribose), and a phosphate group.

Nitrogenous Bases

Purines: Adenine (A) and Guanine (G) - found in both DNA and RNA.
Pyrimidines: Cytosine (C) - found in both DNA and RNA; Thymine (T) - usually found only in DNA; Uracil (U) - usually found only in RNA.

Pentose Sugar

Ribose is the sugar in RNA.
Deoxyribose is the sugar in DNA (lacks an oxygen atom at position 2).

Nucleosides

Formed by covalently linking a nitrogenous base to the number 1 carbon of a sugar.

Nucleotides

Nucleotides are formed when one or more phosphate groups are attached to the 5' carbon of the nucleoside.
The attachment of C1 of the pentose sugar to the N1 of pyrimidine or N9 of purine forms nucleosides.

Primary Structure of DNA

The linear sequence of deoxyribonucleotides (dAMP, dGMP, dTMP, dCMP).
The nitrogenous bases are adenine, guanine, thymine, and cytosine (purines and pyrimidines).
Deoxyribose is the sugar.
Each strand's polarity is 5' to 3'.

Secondary Structure of DNA

DNA exists as a double-stranded molecule, where the two strands are complementary and antiparallel.
The strands are held together by hydrogen bonds.
Adenine pairs with thymine (2 hydrogen bonds); guanine pairs with cytosine (3 hydrogen bonds).
The amount of adenine equals the amount of thymine; the amount of guanine equals the amount of cytosine (Chargaff's rules).
The sugar-phosphate linkages form the backbone of the DNA molecule, and the bases are oriented towards the inside.

Tertiary Structure of DNA – Chromatin Structure

Chromatin is the structure in which DNA exists within cells (eukaryotes).
Chromatin is associated with DNA-binding proteins, including histones and nonhistones.

Histones

Major class of DNA-binding proteins.
Rich in basic amino acids (lysine and arginine), which provide a positive charge to the protein and interact with the negatively charged DNA phosphate group.
Five types: H1, H2A, H2B, H3, and H4.

Nucleosomes

The basic packaging unit of chromatin.
Formed by DNA wrapped around a histone octamer core (composed of two each of H2A, H2B, H3, and H4).

Higher Orders of DNA Structure

The nucleosomes are then supercoiled to create higher order structures – chromatin filaments (30 nm), 300 nm fibrils, 700 nm fibrils, and 1400 nm chromosome.
DNA is condensed to fit into a smaller space.

DNA Denaturation

The process of separating the two strands of a DNA molecule by unwinding due to hydrogen bond breakage.
Occurs when the DNA solution is heated above a certain temperature (melting temperature, Tm). 50% of DNA is half-denatured.

DNA Functions

Carries and transfers genetic information between generations.
Makes copies of itself (replication) and transfers the copies to daughter cells during mitosis.
Creates RNA molecules (transcription) needed for protein synthesis (translation).

Genome

The entire DNA content of a cell.

Genes

Specific areas along the genome that perform a particular function. Often encoding for a specific protein.

Types of DNA

Double-stranded linear: Eukaryotic nuclear chromosome.
Double-stranded circular: Mitochondrial, bacterial chromosome, plasmids, and viral.
Single-stranded circular: small viruses.

Mitochondrial DNA

Circular double-stranded DNA (~16 kb).
Codes for a few genes (enzymes involved in energy production/respiratory chain).
Inherited maternally.
Diseases like MELAS (myopathy, etc.) can arise from mitochondrial DNA deficiencies.

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Description

This quiz explores the fundamental concepts of DNA structure, types of nucleic acids, and the components of nucleotides. Understand the significance of nitrogenous bases, pentose sugars, and the formation of nucleosides. Test your knowledge on the molecular basis of genetic information.