Comprehensive Study Notes for Cumulative Cell Biology Exam

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Preview of Cell Biology

Chemical Bonding and Interactions

Understanding the types of chemical bonds is fundamental to cell biology, as these interactions underpin the structure and function of biomolecules.

Covalent Bonding: Strong bonds formed by the sharing of electron pairs between atoms.
Hydrogen Bonding: Weak bonds important in stabilizing the structures of proteins and nucleic acids.
Hydrophobic Interactions: Nonpolar molecules aggregate to avoid water, influencing membrane and protein structure.

Example: The double helix of DNA is stabilized by hydrogen bonds between complementary bases.

Chemistry of the Cell: Overview

Macromolecules and Condensation Reactions

Macromolecules are synthesized from monomers via condensation reactions, which release water as a byproduct.

Condensation Reaction: Joins two molecules with the removal of water.
Hydrolysis: Breaks bonds by adding water.

Example: Formation of a peptide bond between amino acids during protein synthesis.

Macromolecules: Structure and Function

Levels of Protein Structure

Proteins have four levels of structure, each contributing to their final shape and function.

Primary Structure: Sequence of amino acids.
Secondary Structure: Local folding (α-helix, β-sheet) stabilized by hydrogen bonds.
Tertiary Structure: Overall 3D shape of a single polypeptide.
Quaternary Structure: Association of multiple polypeptide chains.

Example: Hemoglobin's quaternary structure allows cooperative oxygen binding.

Enzymes: Catalysts of Life

Enzyme Function and Specificity

Enzymes are biological catalysts that speed up reactions by lowering activation energy. They are highly specific for their substrates.

Active Site: Region where substrate binds and reaction occurs.
Induced Fit Model: Enzyme changes shape to better fit the substrate.

Equation:

Example: DNA polymerase catalyzes the addition of nucleotides during DNA replication.

Macromolecules II: Nucleic Acids

DNA and RNA Structure

Nucleic acids store and transmit genetic information. DNA is double-stranded, while RNA is usually single-stranded.

DNA: Deoxyribonucleic acid, double helix, stores genetic information.
RNA: Ribonucleic acid, involved in protein synthesis and gene regulation.

Equation:

Example: mRNA carries genetic code from DNA to ribosomes for translation.

Macromolecules III: Polysaccharides, Proteins, and Lipids

Functions and Examples

Macromolecules serve structural, storage, and functional roles in cells.

Polysaccharides: Energy storage (glycogen, starch), structural support (cellulose).
Proteins: Enzymes, structural components, signaling molecules.
Lipids: Membrane structure, energy storage, signaling.

Example: Phospholipids form the bilayer of cell membranes.

Cells and Organelles

Major Organelles and Their Functions

Organelles compartmentalize cellular functions, increasing efficiency and specialization.

Nucleus: Contains genetic material, site of transcription.
Ribosomes: Protein synthesis.
Endoplasmic Reticulum (ER): Protein and lipid synthesis (rough and smooth ER).
Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.
Mitochondria: ATP production via aerobic respiration.
Cytoskeleton: Structural support, intracellular transport, cell movement.

Membranes: Structure and Function

Plasma Membrane Organization

The plasma membrane separates the cell from its environment and regulates the movement of substances.

Phospholipid Bilayer: Hydrophilic heads face outward, hydrophobic tails inward.
Fluid Mosaic Model: Proteins and lipids move laterally within the bilayer.

Example: Membrane proteins act as receptors, channels, or enzymes.

Transport Across Membranes

Mechanisms of Transport

Cells use various mechanisms to move substances across membranes, maintaining homeostasis.

Passive Transport: Diffusion, facilitated diffusion (no energy required).
Active Transport: Requires energy (ATP) to move substances against gradients.
Osmosis: Diffusion of water across a selectively permeable membrane.

Example: Sodium-potassium pump maintains ion gradients in animal cells.

Endomembrane System

Components and Functions

The endomembrane system includes organelles involved in synthesis, modification, and transport of cellular materials.

Includes: Nuclear envelope, ER, Golgi apparatus, lysosomes, vesicles, plasma membrane.
Function: Coordinates protein and lipid synthesis, modification, and transport.

Protein Sorting

Targeting and Transport

Proteins are directed to specific cellular locations by signal sequences and sorting mechanisms.

Signal Peptides: Direct proteins to the ER, mitochondria, or other organelles.
Vesicular Transport: Moves proteins between organelles.

Example: Secretory proteins are synthesized in the ER and transported to the Golgi for modification.

Cytoskeletal Systems

Structure and Function

The cytoskeleton provides structural support, facilitates movement, and organizes cellular components.

Microtubules: Hollow tubes, involved in cell shape, transport, and division.
Microfilaments: Actin filaments, support cell shape and movement.
Intermediate Filaments: Provide mechanical strength.

Example: Microtubules form the mitotic spindle during cell division.

Cellular Movement: Motility and Contractility

Mechanisms of Movement

Cells move and change shape using motor proteins and cytoskeletal elements.

Motor Proteins: Kinesin, dynein, and myosin move along cytoskeletal filaments.
Flagella and Cilia: Specialized structures for movement.

Example: Muscle contraction is driven by actin-myosin interactions.

Structural Basis of Cellular Information: DNA, Chromosomes, and the Nucleus

DNA Organization and Nuclear Structure

DNA is packaged into chromosomes within the nucleus, which regulates gene expression and protects genetic material.

Chromatin: DNA wrapped around histone proteins.
Nuclear Envelope: Double membrane with nuclear pores for transport.

Example: Nuclear pores allow mRNA to exit the nucleus for translation.

DNA Replication and Repair

Mechanisms of Replication

DNA replication is semi-conservative, producing two identical DNA molecules from one original.

DNA Polymerase: Synthesizes new DNA strands using existing strands as templates.
Leading and Lagging Strands: Continuous and discontinuous synthesis, respectively.

Equation:

Example: Okazaki fragments are short DNA segments synthesized on the lagging strand.

Cell Cycle and Mitosis

Phases and Regulation

The cell cycle consists of interphase (G1, S, G2) and mitosis (M phase), regulated by checkpoints to ensure proper division.

G1 Phase: Cell growth and preparation for DNA synthesis.
S Phase: DNA replication.
G2 Phase: Preparation for mitosis.
M Phase: Mitosis and cytokinesis.

Example: The spindle assembly checkpoint ensures chromosomes are properly attached before division.

Cell Cycle Regulation

Checkpoints and Control

Checkpoints monitor and regulate the progression of the cell cycle, preventing errors and ensuring genomic integrity.

G1 Checkpoint: Checks for DNA damage before replication.
G2 Checkpoint: Ensures DNA is fully replicated and undamaged.
M Checkpoint: Confirms all chromosomes are attached to the spindle before anaphase.

Example: p53 protein halts the cell cycle in response to DNA damage.