Biology II Chapter 11 Study Guide

Nucleotides

The building blocks of nucleic acids (DNA & RNA), consisting of a phosphate group, a pentose sugar, and a nitrogenous base.

Differences between DNA and RNA

DNA contains deoxyribose and thymine (T); RNA has ribose and uracil (U).

Purines

Double-ring nitrogenous bases; examples include Adenine (A) and Guanine (G).

Pyrimidines

Single-ring nitrogenous bases; include Thymine (T), Cytosine (C), and Uracil (U).

Covalent Phosphodiester Bonds

Connections that link nucleotides together from the 5’ phosphate to the 3’ hydroxyl.

Directionality of DNA Strand

Refers to the 5’ to 3’ orientation (from phosphate end to hydroxyl end).

Shape of DNA

Double helix structure with antiparallel strands.

Hydrogen Bonds in DNA

Hold the two DNA strands together between complementary bases (A-T, G-C).

Major and Minor Grooves in DNA

Spaces where proteins can interact with DNA for replication and gene expression.

Semi-Conservative Model of DNA Replication

Each new DNA has one old strand and one new strand.

Origin of Replication (ori)

The specific site where replication begins.

Prokaryotic vs. Eukaryotic Replication

Prokaryotes have one origin of replication; Eukaryotes have multiple origins.

Role of Helicase

Unwinds the DNA helix by breaking hydrogen bonds.

Function of Single-Stranded Binding Proteins

Prevent separated DNA strands from reattaching.

DNA Topoisomerase Function

Relieves supercoiling tension ahead of the replication fork.

Function of DNA Primase

Synthesizes short RNA primers to initiate replication.

Function of DNA Polymerase

Synthesizes the new DNA strand in the 5’ to 3’ direction.

Leading Strand

Synthesized continuously in the 5’ to 3’ direction.

Lagging Strand

Synthesized discontinuously using Okazaki fragments.

Function of DNA Ligase

Joins Okazaki fragments by forming covalent bonds.

Accuracy of DNA Polymerase

Proofreading function reduces errors to 1 per 100 million bases.

Telomeres

Repeating non-coding sequences at chromosome ends that prevent DNA loss.

Telomere Shortening

Occurs due to the lagging strand having a 3’ overhang where primers cannot be replaced.

Telomerase

An enzyme that extends telomeres, preventing chromosome shortening.

Connection between Telomerase and Cancer

Telomerase is overactive in 90% of cancers, allowing indefinite cell division.

DNA Packaging into the Nucleus

DNA wraps around histones to form nucleosomes.

30 nm Fiber

A coiled structure of nucleosomes for further DNA compaction.

Radial Loop Domains

Large chromatin loops anchored to the nuclear matrix.

Euchromatin

Loosely packed, transcriptionally active DNA.

Heterochromatin

Densely packed, transcriptionally inactive DNA.

Chromosome Compaction during Cell Division

Chromosomes become highly condensed for mitosis/meiosis.

Deoxyribonucleic Acid (DNA)

The molecule that stores genetic information; double-stranded with deoxyribose sugar.

Ribonucleic Acid (RNA)

A single-stranded nucleic acid involved in protein synthesis; contains ribose sugar.

Phosphate Group in DNA

Part of the DNA backbone, gives DNA a negative charge.

Pentose Sugar

Five-carbon sugar found in nucleotides; deoxyribose in DNA and ribose in RNA.

Base Pairing Rules

A pairs with T (2 hydrogen bonds), G pairs with C (3 hydrogen bonds).

Replication Fork

The area where the DNA strands are separated and copied.

Single-Strand Binding Proteins (SSBs)

Proteins that prevent the re-attachment of separated DNA strands.

Topoisomerase

Enzyme that prevents supercoiling and strain ahead of the replication fork.

Okazaki Fragments

Short DNA segments on the lagging strand that require joining.

Proofreading Function by DNA Polymerase

Detects and corrects errors during DNA synthesis.

Error Rate of DNA Replication

1 mistake per 100 million nucleotides due to proofreading.

Aging and Telomere Shortening

Telomere shortening contributes to cellular aging.

Histones

Proteins around which DNA wraps to form nucleosomes.

Nucleosome

DNA wrapped around histone proteins (146 base pairs per nucleosome).

Chromosomal Territory

The distinct nuclear region occupied by each chromosome.

Centromere

The region where sister chromatids are joined.

Mitosis and Meiosis

Processes involving maximum chromosome compaction for cell division.