Biology Chapter on Genes and Nucleotides

Study Notes

Genes

Sections of DNA containing instructions for mental and physical characteristics inherited from parents.
Basic unit of heredity, contributing to the genetic makeup.
Humans possess approximately 20,000-25,000 protein-coding genes.

Nucleotides

Building blocks (monomers) of nucleic acids RNA and DNA.
Composed of a sugar molecule (ribose in RNA, deoxyribose in DNA), a phosphate group, and a nitrogenous base.
Four bases: adenine (A), cytosine (C), guanine (G), thymine (T).
Base pairing rules: A pairs with T in DNA; A pairs with uracil (U) in RNA; C pairs with G.
DNA and RNA are polymers of long nucleotide chains, held together by hydrogen bonds.

Differences Between RNA and DNA

DNA is double-stranded; RNA is single-stranded.
DNA contains deoxyribose sugar; RNA contains ribose sugar.
In DNA, adenine pairs with thymine; in RNA, adenine pairs with uracil.

DNA

Stands for deoxyribonucleic acid; encodes genetic information.
Characterized by a double helix structure resembling a twisted ladder.
Comprises two strands; 99.9% identical among individuals; unique variations reside in 0.1%.
Capable of self-replication, essential for cell division.
If fully extended, DNA from a single cell measures approximately 2 meters but is tightly coiled within chromosomes.
Pentose sugar forms the backbone of DNA.

Chromosomes

Thread-like structures that contain genes, composed of DNA and histone proteins.
Each DNA molecule is wrapped around histones for structural support.
Human cells contain 46 chromosomes organized into 23 pairs.

Alleles

Different forms of the same gene resulting from mutations, contributing to hereditary variation.

Mutation

Refers to a change in the DNA sequence.
DNA replication is semi-conservative, producing one old strand and one new strand.

Process of DNA Replication

Initiation:
- Helicase enzyme unzips DNA strands by breaking hydrogen bonds.
- Primase synthesizes a small RNA primer.
- DNA polymerase binds to the primer to start elongation.
Elongation:
- DNA polymerase adds nucleotides in one direction (5' to 3') for the leading strand.
- Lagging strand synthesized in short segments known as Okazaki fragments (3' to 5').
Termination:
- Exonuclease removes RNA primers from both strands.
- A second DNA polymerase fills gaps left by primers with DNA nucleotides.
- Ligase enzyme seals the fragments into a continuous double strand.

Description

Explore the fascinating world of genetics with this quiz focused on genes and nucleotides. Learn about how genetic information is passed from parents to offspring and the fundamental components that build DNA and RNA. Test your knowledge on the basic units of heredity and the role of nucleotides in forming these vital molecules.