General Biology: Cell Structure, Genetics, and Human Biology – Study Guide

Cell Structure and Function

Cell Theory

The Cell Theory is a fundamental concept in biology that describes the properties of cells, the basic unit of life.

• All living organisms are composed of one or more cells.

• The cell is the basic unit of structure and organization in organisms.

• All cells arise from pre-existing cells.

Prokaryotic vs. Eukaryotic Cells

Cells are classified as either prokaryotic or eukaryotic based on their structural features.

• Prokaryotic cells lack a true nucleus and membrane-bound organelles. Example: Bacteria.

• Eukaryotic cells have a true nucleus and membrane-bound organelles. Example: Plants, animals, fungi, protists.

• Key difference: Presence of a nucleus and organelles in eukaryotes.

Features of Prokaryotic Cells

• No nucleus; DNA is in the nucleoid region.

• Lack membrane-bound organelles.

• Usually smaller and simpler than eukaryotic cells.

• Cell wall present (in most), plasma membrane, ribosomes, sometimes flagella or pili.

Organelles and Their Functions

Organelles are specialized structures within eukaryotic cells that perform distinct processes.

• Nucleus: Contains genetic material (DNA); controls cell activities.

• Mitochondria: Site of cellular respiration; produces ATP.

• Endoplasmic Reticulum (ER): Synthesizes proteins (rough ER) and lipids (smooth ER).

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.

• Lysosomes: Contain digestive enzymes; break down waste.

• Chloroplasts: (Plants only) Site of photosynthesis.

• Cell Wall: (Plants, fungi, some protists) Provides structure and protection.

Unique Organelles in Plant Cells

• Chloroplasts – photosynthesis.

• Cell wall – structural support.

• Large central vacuole – storage and maintaining cell rigidity.

Genetics and Chromosomes

Chromosomes, Chromatids, and Homologous Chromosomes

• Chromosome: A DNA molecule with part or all of the genetic material of an organism.

• Chromatid: One of two identical halves of a duplicated chromosome.

• Sister chromatids: Two identical chromatids joined by a centromere.

• Homologous chromosomes: Chromosome pairs (one from each parent) with the same genes but possibly different alleles.

Relation: Each chromosome duplicates to form two sister chromatids. Homologous chromosomes are similar but not identical and pair during meiosis.

Chromosome Pairs in Humans

• Humans have 23 pairs of chromosomes (46 total).

• 22 pairs are autosomes; 1 pair is sex chromosomes (XX or XY).

• Pairs allow for genetic diversity and proper segregation during cell division.

Cell Division: Mitosis and Meiosis

Phases of Mitosis

Mitosis is the process by which a cell divides to produce two genetically identical daughter cells.

• Interphase: Cell grows and DNA replicates.

• Prophase: Chromosomes condense, spindle forms.

• Metaphase: Chromosomes align at the cell equator.

• Anaphase: Sister chromatids separate to opposite poles.

• Telophase: Nuclear envelope reforms, chromosomes decondense.

• Cytokinesis: Division of cytoplasm, forming two cells.

Haploid vs. Diploid

• Diploid (2n): Cells with two sets of chromosomes (e.g., somatic cells in humans).

• Haploid (n): Cells with one set of chromosomes (e.g., gametes: sperm and egg).

• Mitosis produces diploid daughter cells; meiosis produces haploid gametes.

Meiosis and Its Phases

Meiosis is a type of cell division that reduces the chromosome number by half, producing four genetically unique haploid cells (gametes).

• Meiosis I: Homologous chromosomes separate.

• Meiosis II: Sister chromatids separate.

• Phases: Prophase I, Metaphase I, Anaphase I, Telophase I, Prophase II, Metaphase II, Anaphase II, Telophase II.

Significance: Increases genetic diversity through crossing over and independent assortment.

Comparison Table: Mitosis vs. Meiosis

Feature	Mitosis	Meiosis
Number of divisions	1	2
Number of daughter cells	2	4
Genetic identity	Identical	Unique
Chromosome number	Diploid (2n)	Haploid (n)
Function	Growth, repair	Gamete production

Cancer and Cell Division

How Cancer Differs from Normal Cell Division

• Cancer cells divide uncontrollably and do not respond to normal regulatory signals.

• They can invade nearby tissues and spread (metastasize) to other parts of the body.

• Normal cells undergo apoptosis (programmed cell death) if damaged; cancer cells often evade this process.

Genetics: Terminology and Principles

Key Terms

• Character: A heritable feature (e.g., flower color).

• Trait: A specific variant of a character (e.g., purple or white flowers).

• Phenotype: Observable physical or physiological traits.

• Genotype: Genetic makeup of an organism.

• Homozygous: Two identical alleles for a gene.

• Heterozygous: Two different alleles for a gene.

Mendelian Genetics

• Principle of Segregation: Each individual has two alleles for each gene, which segregate during gamete formation.

• Principle of Independent Assortment: Genes for different traits can segregate independently during gamete formation.

Monohybrid and Dihybrid Crosses

• Monohybrid cross: Involves one gene (e.g., Aa x Aa).

• Dihybrid cross: Involves two genes (e.g., AaBb x AaBb).

• Use Punnett squares to predict offspring genotypes and phenotypes.

Sex-Linked Inheritance

• Genes located on sex chromosomes (X or Y) show unique inheritance patterns.

• X-linked traits are more commonly expressed in males (XY) than females (XX).

• Example: Color blindness, hemophilia.

Chromosomal Structure and Karyotypes

Karyotype

• A karyotype is an image of an individual's chromosomes arranged in pairs.

• Used to detect chromosomal abnormalities (e.g., Down syndrome).

• Primary uses: Genetic diagnosis, prenatal screening, research.

Human Body: Basic Structure and Function

Human Body Overview

• The human body is composed of multiple organ systems (e.g., circulatory, respiratory, nervous).

• Each system has specialized structures and functions that contribute to overall health and survival.

Additional info: For exam preparation, students should be able to define all key terms, compare processes (e.g., mitosis vs. meiosis), and apply genetic principles using Punnett squares and karyotype analysis.