Chapter_4_Study_Guide

Genetics and Cellular Function

I. DNA and RNA—The Nucleic Acids

• Nucleotides Composition

  • Composed of a sugar, phosphate group, and a nitrogenous base.

  • Three pyrimidines: Cytosine (C), Thymine (T), and Uracil.

  • Two purines: Adenine (A) and Guanine (G).

• Structure of DNA

  • Resembles a spiral staircase with

    • Backbones of phosphate groups alternating with deoxyribose sugar.

    • Nitrogenous bases forming connections between backbones.

    • A–T pair forms two hydrogen bonds; C–G pair forms three hydrogen bonds.

  • Base pairs: A–T and C–G; following the law of complementary base pairing, allows prediction of one strand's sequence based on the other.

  • Essential function: Encodes for proteins synthesized by cells.

• Chromatin

  • DNA complexed with proteins; forms fine filamentous material.

  • Human chromatin consists of 46 chromosomes; DNA is about 2 m long when unwound but packed in the nucleus.

  • Appears as beads on a string with segments called nucleosomes.

  • DNA replication leads to two sister chromatids joined at a centromere with a kinetochore.

II. RNA Types

• Types of RNA

  • mRNA (messenger), rRNA (ribosomal), and tRNA (transfer).

• Differences Between RNA and DNA

  • RNA is smaller, single-stranded, and contains ribose (not deoxyribose); uracil replaces thymine.

• Function of RNA

  • Interprets DNA code and directs protein synthesis.

III. Genes and Their Action

• Definition of a Gene

  • Information-containing segment of DNA coding for RNA production, primarily for protein synthesis.

• Human Chromosomes

  • 46 chromosomes in two sets of 23 (one from each parent), collectively called the genome (c. 3.1 billion nucleotide pairs).

• Human Genome Project (HGP)

  • Revealed sequence of over 99% of the genome.

• Genomics

  • Field studying genomes and interactions of genes and noncoding DNA.

IV. Genetic Code

• DNA and RNA Collaboration

  • The genetic code specifies protein synthesis for cells; different cells express different genes.

• Transcription

  • Process of DNA copying into RNA.

• Translation

  • Conversion of nucleotides into amino acids; involves secondary and tertiary protein structures and sometimes quaternary structures.

• Gene Regulation

  • Factors influence gene expression, including regulatory proteins that interact with RNA polymerase and DNA.

V. DNA Replication and Cell Cycle

• DNA Replication

  • Essential before cell division, involving complementary base pairing.

  • Mutations occur from replication errors or environmental factors; most do not affect protein function due to noncoding DNA.

• Cell Cycle Phases

  • Interphase includes G0 (resting), G1 (growth), S (synthesis), G2 (pre-cell division) phases.

  • Division Mechanism

    • Mitosis (general cell division) vs. meiosis (gamete production).

VI. Mitosis Phases

• Mitosis Stages: Prophase, Metaphase, Anaphase, and Telophase

  • Prophase: Chromosomes condense and align; nuclear envelope disintegrates.

  • Metaphase: Chromosomes await separation.

  • Anaphase: Chromatids separate to become daughter chromosomes.

  • Telophase: Daughter chromosomes cluster; new nuclear envelope forms.

• Cytokinesis

  • Division of cytoplasm, led by myosin interacting with actin filaments, creating cleavage furrow.

VII. Heredity and Chromosomes

• Heredity

  • Transmission of genetic traits from parents to offspring.

• Karyotype

  • Arrangement of chromosomes, with homologous chromosomes forming pairs.

  • Diploid cells have 23 pairs; haploid sperm and egg cells have half.

VIII. Genes and Alleles

• Gene Functions

  • Chromosomes carry multiple genes; each gene has a specific locus.

  • Alleles may be dominant or recessive.

• Mendelian Genetics

  • Punnett squares illustrate inheritance patterns; heterozygous carriers may possess recessive alleles for diseases.

• Multiple Alleles and Codominance

  • ABO blood groups demonstrate codominance; alleles exhibit dominance and recessiveness.

IX. Genetic Variation and Epigenetics

• Polygenic Inheritance

  • Multiple genes contribute to single traits (e.g., eye and skin color).

• Sex-Linked Traits

  • Carried on sex chromosomes, affecting inheritance patterns between sexes.

• Environmental Influence

  • Gene expression impacted by external factors, including nutrition.

• Epigenetics

  • Study of hereditary changes not caused by DNA mutations; DNA methylation as a means of altering gene expression.