Cell Structure and Function

Overview of Cell Organelles and Structures

Cells are the basic units of life, and their internal structures (organelles) perform specialized functions necessary for survival and reproduction.

• Nucleus: Contains genetic material (DNA) and controls cellular activities.

• Ribosomes: Sites of protein synthesis.

• Endoplasmic Reticulum (ER): Rough ER is studded with ribosomes and synthesizes proteins; smooth ER synthesizes lipids and detoxifies chemicals.

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.

• Lysosomes: Contain digestive enzymes to break down waste.

• Mitochondria: Powerhouse of the cell; site of cellular respiration and ATP production.

• Chloroplasts: (in plants) Site of photosynthesis.

• Cell Membrane: Semi-permeable barrier controlling entry and exit of substances.

• Cell Wall: (in plants, fungi, and some protists) Provides structural support.

• Cytoskeleton: Network of protein filaments for cell shape, movement, and division.

• Central Vacuole: (in plants) Stores water, nutrients, and waste products.

Example: Plant cells have both chloroplasts and a cell wall, while animal cells do not.

Prokaryotic vs. Eukaryotic Cells

• Prokaryotic cells: Lack a nucleus and membrane-bound organelles; DNA is in the nucleoid region (e.g., bacteria, archaea).

• Eukaryotic cells: Have a nucleus and membrane-bound organelles (e.g., plants, animals, fungi, protists).

Key Difference: Presence of a nucleus and organelles in eukaryotes.

Plant vs. Animal Cells

• Plant cells: Have a cell wall, chloroplasts, and a large central vacuole.

• Animal cells: Lack cell walls and chloroplasts, have smaller vacuoles.

ATP and Energy Release

ATP (adenosine triphosphate) is the primary energy carrier in cells. When ATP is hydrolyzed to ADP (adenosine diphosphate), energy is released for cellular processes.

Digestion and Absorption

• Digestion: Breakdown of food into smaller molecules.

• Absorption: Uptake of nutrients into the bloodstream or cells.

These processes are essential for providing energy and building blocks for growth and repair.

Cellular Respiration and Metabolism

Cellular Respiration Overview

Cellular respiration is the process by which cells convert glucose and oxygen into ATP, carbon dioxide, and water.

• General Equation:

• Glycolysis: Occurs in the cytoplasm; breaks glucose into pyruvate.

• Krebs Cycle (Citric Acid Cycle): Occurs in mitochondria; processes pyruvate to produce electron carriers.

• Electron Transport Chain: Uses electrons from carriers to produce ATP; oxygen is the final electron acceptor.

Importance of Oxygen

Oxygen is essential for the electron transport chain to function, allowing for efficient ATP production.

Comparison: Aerobic vs. Anaerobic Respiration

• Aerobic respiration: Requires oxygen, produces more ATP.

• Anaerobic respiration (fermentation): Occurs without oxygen, produces less ATP and byproducts like lactic acid or ethanol.

Genetics and Molecular Biology

DNA Structure and Function

• DNA (deoxyribonucleic acid): Double helix structure composed of nucleotides (adenine, thymine, cytosine, guanine).

• Genes: Segments of DNA that code for proteins.

• Chromosomes: DNA packaged with proteins; humans have 23 pairs.

DNA Replication

Process by which DNA makes a copy of itself before cell division.

Protein Synthesis

• Transcription: DNA is transcribed into messenger RNA (mRNA).

• Translation: mRNA is translated into a protein at the ribosome.

Genetic Code

The genetic code is universal and redundant; each codon (three nucleotides) codes for one amino acid.

Mutations

• Definition: Changes in DNA sequence.

• Causes: Errors in replication, environmental factors.

• Effects: Can be harmful, beneficial, or neutral; source of genetic variation.

Sexual vs. Asexual Reproduction

• Sexual reproduction: Involves gametes (egg and sperm), increases genetic diversity.

• Asexual reproduction: Offspring are genetically identical to parent.

Meiosis and Chromosomes

• Meiosis: Cell division that produces gametes with half the chromosome number (haploid).

• Homologous pairs: Chromosome pairs, one from each parent.

• Human diploid cell: 23 pairs (46 chromosomes); haploid gamete: 23 chromosomes.

Hardy-Weinberg Equilibrium

Describes a non-evolving population; allele and genotype frequencies remain constant if certain conditions are met.

• Equation:

Where p and q are the frequencies of two alleles.

Evolution and Natural Selection

Natural Selection and Adaptation

• Natural selection: Process by which individuals with advantageous traits survive and reproduce more successfully.

• Adaptation: Trait that increases an organism's fitness in its environment.

Types of Selection

• Directional selection: Favors one extreme phenotype.

• Stabilizing selection: Favors intermediate phenotypes.

• Disruptive selection: Favors both extreme phenotypes.

Sexual Selection

• Definition: Selection for traits that increase mating success.

• Examples: Bright plumage in birds, antlers in deer.

Speciation

• Definition: Formation of new species.

• Types: Allopatric (geographic isolation), sympatric (without geographic isolation).

Microevolution vs. Macroevolution

• Microevolution: Small-scale changes within a population (e.g., allele frequency shifts).

• Macroevolution: Large-scale changes leading to new species or groups.

Convergent Evolution

Unrelated species evolve similar traits due to similar environmental pressures (e.g., wings in bats and birds).

Classification and Phylogeny

Taxonomic Hierarchy

• Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species

Phylogenetic Trees

• Definition: Diagrams showing evolutionary relationships.

• Clade: Group of organisms with a common ancestor.

• Horizontal gene transfer: Movement of genes between species, can affect tree structure.

Monophyly and Polyphyly

• Monophyletic group: Includes a common ancestor and all its descendants.

• Polyphyletic group: Does not include the most recent common ancestor.

Table: Comparison of Cell Types

Additional info:

• Some questions in the original file are highlighted in red, indicating their importance for exam preparation.

• Students should be able to define, compare, and apply these concepts to new scenarios.