EXAM 2 REVIEW
Chapter 4 - Cell Structure
Fundamental Units of Life
Cells are the building blocks of all organisms.
In single-celled organisms, the cell is everything.
Organization in Multicellular Organisms
Hierarchical organization:
Cells are the basic unit.
Tissues are groups of interconnected cells with a common function.
Organs are composed of different tissues.
Organ systems consist of multiple organs working together.
Organisms are formed by multiple systems functioning together.
Cell Size
Cells vary in size, most are microscopic and cannot be seen without microscopy.
Magnification and Resolving Power
Critical parameters in microscopy that affect detail visibility.
Cell Theory
An underlying principle of biology:
Cells are the basic units of life.
All living organisms are made of cells.
All cells arise from preexisting cells.
Common Components of Cells
Four common components:
Plasma Membrane: Encloses the cell, separates interior from the environment.
Cytoplasm: Consists of cytosol and other components.
DNA: Genetic material of the cell.
Ribosomes: Synthesize proteins.
Characteristics of Prokaryotes
Lack membrane-enclosed internal compartments (e.g., nucleus).
Most have a cell wall composed of peptidoglycan.
Believed to resemble early life forms; includes Archaea and Bacteria domains.
Generalized Structure of Prokaryotic Cells
Contains chromosomal DNA in a nucleoid, ribosomes, and a cell membrane surrounded by a cell wall.
Size Comparison
Prokaryotic cells are generally smaller than eukaryotic cells.
Favorable surface area to volume ratio for efficient material transport.
Lack specialized internal structures found in eukaryotes.
Factors Limiting Cell Size
Metabolic requirements impose upper limits on cell size:
Maximum sizes include:
Human height: 1 m
Length of some nerve/muscle cells: 0.1 m
Chicken egg: 1 cm
Frog egg: 1 mm
Human egg: 100 μm
Most plant and animal cells: 30 μm
Most bacteria: 1 μm
Smallest bacteria: 0.25 μm
Viruses: 100 nm
Proteins: 10 nm
Small molecules: 1 nm
Atoms: 0.1 nm.
Surface Area to Volume Ratio
Formula:
Surface Area (SA) = $4 \, \pi \, r^2$
Volume (V) = $\frac{4}{3} \pi r^3$
As a cell grows, volume increases faster than surface area.
Decreased SA/V ratio leads to the need for cell division.
Eukaryotic Cells Structure
Contains various organelles, including:
Nucleus, Nucleolus, Plasma Membrane, Various types of Endoplasmic Reticulum (ER), Mitochondrion, Golgi Apparatus, Lysosomes, etc.
Eukaryotic plasma membrane features:
Glycoproteins and Glycolipids.
Integral and Peripheral proteins.
Cytoplasm Details
Region between the plasma membrane and nuclear envelope, contains organelles suspended in semi-solid cytosol.
70-80% is water.
Nucleus
Typically largest organelle, Contains:
Nuclear Envelope: Double membrane with nuclear pores regulating molecular flow.
Nucleolus: Site of ribosome assembly.
Chromatin: DNA in various forms.
Ribosomes
Composed of RNA and proteins, critical for protein synthesis.
Mitochondria
Conversion site of stored energy to ATP; features cristae (folds) and mitochondrial matrix.
Peroxisomes
Organelle involved in fatty acid and amino acid breakdown; detoxification.
Differences Between Animal and Plant Cells
Animal Cells:
Centrioles, lysosomes, multiple small vacuoles.
Plant Cells:
Cell wall (cellulose), chloroplasts, large central vacuole, Plasmodesmata for communication between cells.
Chloroplasts
Site of photosynthesis, has its own DNA and ribosomes, contains thylakoids organized in granum.
Central Vacuole
Main reservoir in plant cells, regulates water concentration and aids in cell expansion.
Endomembrane System
Includes nuclear envelope, ER, Golgi apparatus, lysosomes, vesicles for lipid and protein transport and processing.
Lysosomes
Contain digestive enzymes; breakdown large biomolecules and organelles.
Endoplasmic Reticulum (ER)
Two types: Smooth (SER) and Rough (RER).
RER: Protein synthesis and initial modification.
SER: Lipid synthesis and detoxification processes.
Golgi Apparatus
Modifies, sorts, and packages lipids/proteins from the ER.
Cytoskeleton
Network of protein fibers maintaining cell shape, facilitating movement within cells, and enabling cellular movement in multicellular organisms.
Three components: Microfilaments, Intermediate filaments, Microtubules.
Extracellular Structures
Plant Cell Wall: Provides support and protection; includes plasmodesmata for cell connectivity.
Extracellular Matrix in Animals: Composed of collagens and glycoproteins.
Intercellular Junctions
Specialized connections aiding cell adhesion and communication:
Tight junctions: Prevent leakage.
Desmosomes: Provide mechanical strength.
Gap junctions: Allow molecular exchange.
Endosymbiosis Theory
Explains origin of mitochondria and chloroplasts as ancestral eukaryotic cells engulfed smaller prokaryotes; mutualistic evolution led to permanent organelles.
Key characteristics promoting this theory include organelles having their DNA and ribosomes resembling independent prokaryotes; significant research by Lynn Margulis.
Chapter 5
5.1 Components and Structure
Modern scientists refer to the plasma membrane as the fluid mosaic model. A phospholipid bilayer comprises the plasma membrane, with hydrophobic, fatty acid tails in contact with each other. The membrane's landscape is studded with proteins, some which span the membrane. Some of these proteins serve to transport materials into or out of the cell. Carbohydrates are attached to some of the proteins and lipids on the membrane's outward-facing surface, forming complexes that function to identify the cell to other cells. The membrane's fluid nature is due to temperature, fatty acid tail configuration (some kinked by double bonds), cholesterol presence embedded in the membrane, and the mosaic nature of the proteins and protein-carbohydrate combinations, which are not firmly fixed in place. Plasma membranes enclose and define the cells' borders. Not static, they are dynamic and constantly in flux.
5.2 Passive Transport
The passive transport forms, diffusion and osmosis, move materials of small molecular weight across membranes. Substances diffuse from high to lower concentration areas, and this process continues until the substance evenly distributes itself in a system. In solutions containing more than one substance, each molecule type diffuses according to its own concentration gradient, independent of other substances diffusing. Many factors can affect the diffusion rate, such as concentration gradient, diffusing, particle sizes, and the system's temperature.
In living systems, the plasma membrane mediates substances diffusing in and out of cells. Some materials diffuse readily through the membrane, but others are hindered and only can pass through due to specialized proteins such as channels and transporters. The chemistry of living things occurs in aqueous solutions, and balancing the concentrations of those solutions is an ongoing problem. In living systems, diffusing some substances would be slow or difficult without membrane proteins that facilitate transport.
5.3 Active Transport
The combined gradient that affects an ion includes its concentration gradient and its electrical gradient. A positive ion, for example, might diffuse into a new area, down its concentration gradient, but if it is diffusing into an area of net positive charge, its electrical gradient hampers its diffusion. When dealing with ions in aqueous solutions, one must consider electrochemical and concentration gradient combinations, rather than just the concentration gradient alone. Living cells need certain substances that exist inside the cell in concentrations greater than they exist in the extracellular space. Moving substances up their electrochemical gradients requires energy from the cell. Active transport uses energy stored in ATP to fuel this transport. Active transport of small molecular-sized materials uses integral proteins in the cell membrane to move the materials. These proteins are analogous to pumps. Some pumps, which carry out primary active transport, couple directly with ATP to drive their action. In co-transport (or secondary active transport), energy from primary transport can move another substance into the cell and up its concentration gradient.
5.4 Bulk Transport
Active transport methods require directly using ATP to fuel the transport. In a process scientists call phagocytosis, other cells can engulf large particles, such as macromolecules, cell parts, or whole cells. In phagocytosis, a portion of the membrane invaginates and flows around the particle, eventually pinching off and leaving the particle entirely enclosed by a plasma membrane's envelope. The cell breaks down vesicle contents, with the particles either used as food or dispatched. Pinocytosis is a similar process on a smaller scale. The plasma membrane invaginates and pinches off, producing a small envelope of fluid from outside the cell. Pinocytosis imports substances that the cell needs from the extracellular fluid. The cell expels waste in a similar but reverse manner. It pushes a membranous vacuole to the plasma membrane, allowing the vacuole to fuse with the membrane and incorporate itself into the membrane structure, releasing its contents to the exterior.
Chapter 6 Metabolism Overview
Definition of Metabolism: Totality of an organism’s chemical reactions.
Involves thousands of biochemical reactions requiring energy transformations.
Transforms matter and energy adhering to the laws of physics.
Metabolic Pathways
Metabolic Pathway: A series of chemical reactions where the product of one reaction serves as a reactant for the next.
Each reaction in the pathway is catalyzed by a specific enzyme.
Example Structure:
Enzyme 1: Converts A to B
Enzyme 2: Converts B to C
Enzyme 3: Converts C to D
Types of Metabolic Pathways
Catabolic Pathways:
Break down complex molecules (food) into simpler ones.
Release energy.
Anabolic Pathways:
Build more complex molecules.
Require energy.
Evolution of Metabolic Pathways
Life shares several metabolic pathways, suggesting common ancestry and evolutionary divergence.
Specialized enzymes evolved to help organisms adapt to their environments.
Energy
Definition of Energy: Capacity to cause change or do work.
Forms of Energy:
Potential Energy (stored energy in matter):
Chemical bonds
Concentration gradients
Electrical potential
Kinetic Energy (energy of movement):
Heat (molecular motion)
Mechanical energy (moving molecules)
Electrical energy (moving charged particles)
Conversion of Energy
Energy can be converted from one form to another, such as:
Diver converting potential energy to kinetic energy while diving.
Climbing converts kinetic energy to potential energy.
Laws of Energy Transformation
Thermodynamics: Study of energy transformations.
Open Systems: Organisms absorb and release energy and matter.
Closed Systems: Matter and energy cannot enter or leave.
First Law of Thermodynamics
Energy cannot be created or destroyed; only transformed.
Example: Chemical energy to heat.
Second Law of Thermodynamics
Energy transfer increases entropy (disorder) of the universe.
No process is 100% efficient; energy is lost as heat.
Entropy
Entropy (S): Measure of disorder or randomness, representing energy dispersal.
Biological systems maintain order while contributing to increased entropy in the surroundings.
Spontaneous Reactions
Definition: Reactions that occur without energy input, increasing entropy.
Spontaneous reactions can vary in rate (quick vs. slow).
Free Energy (G)
Gibbs Free Energy: Energy available to do work; change in free energy (∆G) determines if a reaction is spontaneous.
Equation: \Delta G = \Delta H - T\Delta S
Where, (\Delta H) is total energy change, (T) is temperature in Kelvin, and (\Delta S) is change in entropy.
Exergonic Reactions (Catabolic)
If products have less potential energy than reactants, reaction releases energy.
(\Delta G < 0): Spontaneous.
Endergonic Reactions (Anabolic)
If products have more potential energy than reactants, the reaction requires energy input.
(\Delta G > 0): Non-Spontaneous.
Reaction Coupling
Energy from exergonic reactions can power endergonic reactions.
ATP plays a crucial role in performing work in cells.
ATP Hydrolysis
ATP (adenosine triphosphate): Main energy shuttle in cells.
Hydrolysis: Release of energy occurs when the terminal phosphate bond is broken.
Coupling ATP hydrolysis with endergonic reactions is essential for energy transfer.
Activation Energy (EA)
Activation Energy: Initial energy required to start a chemical reaction; represents the energy barrier.
Enzymes lower EA, aiding in catalyzing reactions.
Enzymes as Catalysts
Enzymes: Biological catalysts that speed up reactions by lowering EA.
Specific for substrates, not consumed in reactions.
Form enzyme-substrate complexes, converting reactants to products efficiently.
Factors Affecting Enzyme Activity
Local Conditions: Enzyme activity is affected by ion concentration, pH, temperature, and regulatory molecules.
Regulation of Enzymes
Enzymes can be regulated positively or negatively, affecting activity and function based on the organism's needs.
Competitive Inhibition: Inhibitor competes for enzyme's active site.
Noncompetitive Inhibition: Inhibitor binds elsewhere, altering enzyme shape.
Feedback Inhibition: End product of a pathway shuts down the pathway.
Metabolism Overview
Definition of Metabolism: Totality of an organism’s chemical reactions.
Involves thousands of biochemical reactions requiring energy transformations.
Transforms matter and energy adhering to the laws of physics.
Metabolic Pathways
Metabolic Pathway: A series of chemical reactions where the product of one reaction serves as a reactant for the next.
Each reaction in the pathway is catalyzed by a specific enzyme.
Example Structure:
Enzyme 1: Converts A to B
Enzyme 2: Converts B to C
Enzyme 3: Converts C to D
Types of Metabolic Pathways
Catabolic Pathways:
Break down complex molecules (food) into simpler ones.
Release energy.
Anabolic Pathways:
Build more complex molecules.
Require energy.
Evolution of Metabolic Pathways
Life shares several metabolic pathways, suggesting common ancestry and evolutionary divergence.
Specialized enzymes evolved to help organisms adapt to their environments.
Energy
Definition of Energy: Capacity to cause change or do work.
Forms of Energy:
Potential Energy (stored energy in matter):
Chemical bonds
Concentration gradients
Electrical potential
Kinetic Energy (energy of movement):
Heat (molecular motion)
Mechanical energy (moving molecules)
Electrical energy (moving charged particles)
Conversion of Energy
Energy can be converted from one form to another, such as:
Diver converting potential energy to kinetic energy while diving.
Climbing converts kinetic energy to potential energy.
Laws of Energy Transformation
Thermodynamics: Study of energy transformations.
Open Systems: Organisms absorb and release energy and matter.
Closed Systems: Matter and energy cannot enter or leave.
First Law of Thermodynamics
Energy cannot be created or destroyed; only transformed.
Example: Chemical energy to heat.
Second Law of Thermodynamics
Energy transfer increases entropy (disorder) of the universe.
No process is 100% efficient; energy is lost as heat.
Entropy
Entropy (S): Measure of disorder or randomness, representing energy dispersal.
Biological systems maintain order while contributing to increased entropy in the surroundings.
Spontaneous Reactions
Definition: Reactions that occur without energy input, increasing entropy.
Spontaneous reactions can vary in rate (quick vs. slow).
Free Energy (G)
Gibbs Free Energy: Energy available to do work; change in free energy (∆G) determines if a reaction is spontaneous.
Equation: \Delta G = \Delta H - T\Delta S
Where, (\Delta H) is total energy change, (T) is temperature in Kelvin, and (\Delta S) is change in entropy.
Exergonic Reactions (Catabolic)
If products have less potential energy than reactants, reaction releases energy.
(\Delta G < 0): Spontaneous.
Endergonic Reactions (Anabolic)
If products have more potential energy than reactants, the reaction requires energy input.
(\Delta G > 0): Non-Spontaneous.
Reaction Coupling
Energy from exergonic reactions can power endergonic reactions.
ATP plays a crucial role in performing work in cells.
ATP Hydrolysis
ATP (adenosine triphosphate): Main energy shuttle in cells.
Hydrolysis: Release of energy occurs when the terminal phosphate bond is broken.
Coupling ATP hydrolysis with endergonic reactions is essential for energy transfer.
Activation Energy (EA)
Activation Energy: Initial energy required to start a chemical reaction; represents the energy barrier.
Enzymes lower EA, aiding in catalyzing reactions.
Enzymes as Catalysts
Enzymes: Biological catalysts that speed up reactions by lowering EA.
Specific for substrates, not consumed in reactions.
Form enzyme-substrate complexes, converting reactants to products efficiently.
Factors Affecting Enzyme Activity
Local Conditions: Enzyme activity is affected by ion concentration, pH, temperature, and regulatory molecules.
Regulation of Enzymes
Enzymes can be regulated positively or negatively, affecting activity and function based on the organism's needs.
Competitive Inhibition: Inhibitor competes for enzyme's active site.
Noncompetitive Inhibition: Inhibitor binds elsewhere, altering enzyme shape.
Feedback Inhibition: End product of a pathway shuts down the pathway.
Chapter 10: Cell Reproduction
Key Objectives
Explain differences in chromosome constitution between somatic cells and gametes.
Name macromolecules that comprise chromosomes.
Describe key terms related to chromosomes, including chromatids, euchromatin, heterochromatin, genome, gene, homologous chromosomes.
Describe the function of mitosis and cytokinesis.
Sketch and describe different phases of the cell cycle.
Sketch and describe stages of mitosis.
Explain microtubules' role during mitosis.
Compare cell division in eukaryotes and prokaryotes.
Discuss roles of internal and external signals in the cell cycle.
Explain cyclin-CDKs’ role in cell cycle progression control.
Describe MPF structure and function during cell cycle.
Explain G1, G2, and M checkpoints.
Discuss transformations of normal cells into cancer cells.
Identify differences between benign and malignant tumors.
Explain roles of proto-oncogenes, oncogenes, and tumor suppressor genes in cancer biology.
Describe multihit/multistep model of cancer with examples.
Discuss cancer treatment options.
Factors Limiting Cell Size
Metabolic Requirements
Set critical upper limits on cell size due to metabolic demands. Sizes include:
10 m: Human height
1 m: Length of some nerve and muscle cells
0.1 m: Chicken egg
1 cm: Frog egg
1 mm: Human egg
100 μm: Most plant and animal cells
10 μm: Nucleus
1 μm: Mitochondrion
100 nm: Smallest bacteria
10 nm: Ribosomes
1 nm: Proteins
0.1 nm: Atoms
Surface Area to Volume Ratio
As cells grow, volume increases faster than surface area.
At a certain size, insufficient surface area is available to service cell's interior, causing it to stop growing and divide.
Cell Division in Multicellular Organisms
Purpose
Key facets of cell division in multicellular organisms:
Development from a fertilized cell.
Growth and development. (Example: Sand dollar embryo post-division. 200 µm, 20 µm)
Repair (Example: Dividing bone marrow cells produce new blood cells).
Cell Division in Unicellular Organisms
Purpose
Unicellular organisms reproduce through cell division.
Example: An amoeba divides into two new independent cells.
Terminology Definitions
Genome
Definition: Entire set of genetic material in an organism.
Structure: All DNA across all chromosomes, encompassing genes and noncoding regions.
Example: Human genome ≈ 3 billion base pairs of DNA.
Chromosome
Definition: Single long DNA coiled around histone proteins.
Structure: Condensed form of chromatin.
Function: Carries multiple genes; visible during cell division.
Example: Humans have 46 chromosomes (23 pairs).
Chromatin
Definition: A complex of DNA and histone proteins.
Structure: Uncoiled, thread-like form.
Function: Packages DNA in the nucleus; controls gene accessibility.
Note: Condenses into chromosomes during cell division.
Euchromatin
Definition: Lightly packed form of chromatin.
Structure: Loosely coiled.
Function: Transcriptionally active region where genes are expressed.
Visual: Appears light under a microscope.
Heterochromatin
Definition: Densely packed form of chromatin.
Structure: Tightly coiled.
Function: Transcriptionally inactive; silences genes.
Location: Primarily at centromeres and telomeres.
Gene
Definition: Specific sequence of DNA that codes for a protein or RNA molecule.
Structure: Small segment of a chromosome.
Function: Basic unit of heredity; determines specific traits.
Example: Gene coding for globin proteins in red blood cells.
Note: Different versions (alleles) influence phenotypes, e.g., earlobe attachment.
Chromatid
Definition: One of two identical copies of a replicated chromosome.
Function: Ensures identical DNA distribution during cell division.
Structure: Two sister chromatids make one duplicated chromosome.
Homologous Chromosomes
Definition: Pair of chromosomes (one from each parent) with the same genes at corresponding loci.
Function: Pair during meiosis for recombination and proper segregation.
Note: Similar in size, shape, and gene order, e.g., Chromosome 1 from mother and father.
Visualization Metaphors for Chromosomal Structures
Analogy for Chromatin: Imagine chromatin as yarn stretched on spools (histones).
Euchromatin: Loosely wound yarn is accessible for knitting (gene expression).
Heterochromatin: Tightly wound yarn is inaccessible (gene silencing).
Chromosomes: Tightly packed skeins of yarn prepared for transport.
Chromatids: Two identical skeins bound together at a centromere (narrow waist).
Chromatids Details
Sister Chromatids
Structure: Formed after DNA replication, consists of two identical copies connected at the centromere.
Separation Mechanism: Mechanical processes separate sister chromatids into two chromosomes during cell division.
DNA Compaction
Mechanism: Approximately 2 m of DNA is compacted within each nucleus by winding around histone octamers (beads on a string).
Chromosome Sets in Animals
Somatic Cells
Contain two sets of chromosomes (soma, meaning "body").
Gametes
Contain one set of chromosomes (sex cells, sperm and egg).
Examples
Two sets of Chromosome #1 from mother and father.
One Chromosome #1 set is a combination from both parents.
The Cell Cycle and Cell Division
Cell Cycle Definition
An ordered series of events in a cell’s life cycle; continuity of life is based on reproduction of cells (cell division).
Cell Division Process
Integral to the cell cycle but not the only aspect.
Chromosome Distribution During Division
Preparation for Cell Division
DNA replication and chromosomal condensation in anticipation of cell division.
Eukaryotic Cell Division Overview
Comprised of:
Mitosis: Division of the nucleus.
Cytokinesis: Division of the cytoplasm.
Meiosis: Production of sex cells post chromosome number reduction.
Phases of the Cell Cycle
Interphase (blue, 90% of cell cycle)
G1 Phase (First Gap): Biochemical activity, cell growth, cytoplasm increase, protein synthesis.
S Phase: DNA synthesis/replication.
G2 Phase (Second Gap): Cell growth, energy replenishment, organelle reproduction, cytoskeleton breakdown.
Mitotic Phase (red): Actual division phase including the mitosis of the nucleus and the division of cytoplasm (cytokinesis).
Mitosis Phases
Key Stages: Mitosis consists of:
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Mnemonic: PPMAT (for ordering the phases).
Role of Microtubules in Mitosis
Microtubules: Critical for organizing the mitotic spindle and controlling chromosome movement during mitosis and meiosis; arise from centrosomes.
Cytokinesis Processes in Animal and Plant Cells
Animal Cells: Cytokinesis occurs through cleavage furrow formation via microfilaments (actin and myosin).
Plant Cells: Vesicles from the Golgi apparatus form a cell plate at the center by coalescing during cytokinesis.
Prokaryotic Cell Division
Process: Prokaryotes do not undergo mitosis but reproduce through binary fission.
Binary Fission Mechanism
Replication: The bacterial chromosome replicates, and daughter chromosomes move apart through FtsZ protein function forming the septum.
Evolution of Mitosis
Evolutionary Perspective: Mitosis likely evolved from bacterial division; certain protists exhibit division types that bridge binary fission and typical eukaryotic mitosis.
Regulation of the Cell Cycle
Control System: The cell cycle is regulated by a complex molecular control system influenced by internal and external signals.
Checkpoints: Govern progress through phases (G1, G2, and M checkpoints) based on predetermined conditions:
G1 Checkpoint: Determines if conditions favor cell division.
G2 Checkpoint: Checks for cell size and DNA replication completion; prevents entry into mitosis if conditions are unmet.
M Checkpoint: Ensures all sister chromatids are properly attached to spindle fibers before mitosis proceeds.
Cyclins, Cyclin-Dependent Kinases (Cdks)
Regulatory Proteins: Cyclins and Cdks regulate cell cycle advancement.
CDK Activation: Cyclins activate Cdks that phosphorylate proteins to encourage cell cycle progression.
MPF (Mitosis Promoting Factor): A cyclin-Cdk complex that initiates mitosis. Cyclin accumulation leads to MPF activity rising, driving the progression through the cycle.
Cancer and Cell Cycle Disruption
Cancer Definition: A collection of diseases associated with uncontrolled cell growth.
Causes: Genetic changes disrupting normal cell cycle control, with innate roles also in DNA repair and embryonic development.
Tumor Types: Benign tumors are localized with clean boundaries, while malignant tumors invade and can metastasize into other tissues.
Key Players in Cancer Genetics
Proto-oncogenes: Normal genes regulating cell division; mutations can turn these genes into oncogenes, promoting unchecked growth.
Tumor Suppressor Genes: Genes that normally limit cell division; mutations lead to loss of function, allowing uncontrolled division.
Multi-Hit Model: Cancer cell development often requires multiple mutations accumulating to phase into a cancerous state.
Treatment Options for Cancer
Treatments vary and target cell division; common examples include therapies disrupting DNA replication or utilizing agents like Taxol, which target mitotic spindle function.
Specific Examples of Cancer Genetics
Ras Oncogene: A signaling protein regulating the cell cycle. Mutations can lead to overactivity.
p53 Tumor Suppressor: Regulates cell cycle inhibition and DNA repair; mutations can prevent cell death and progression through the cycle.
Breast Cancer Genetics: Associated with BRCA gene mutations impacting DNA repair mechanisms, leading to elevated cancer risks due to fewer required mutations for onset.
External Causes: Certain viruses and mutagens can promote the genetic changes leading to cancer.
The Importance of Early Detection
Detection and Treatment: Early detection of cancer significantly improves treatment outcomes and survivability.
Chapter 14
DNA Overview
Definition: Deoxyribonucleic acid (DNA) serves as the fundamental substance of inheritance, functioning as the genetic material that encapsulates and transmits hereditary information from one generation to the next.
Significance: It precisely directs the synthesis of proteins and RNA molecules, thereby orchestrating the development and expression of all inherited traits and characteristics in living organisms.
Structure: DNA is a complex macromolecule composed of repeating monomer units known as nucleotides, which are linked together to form two long polynucleotide strands that twist around each other to create a distinctive double-stranded helix structure.
DNA in the Cell
Chromosome: Within eukaryotic cells, all of a cell's DNA is meticulously organized into structures called chromosomes, collectively constituting the organism's entire genetic complement, known as the genome. Prokaryotic cells typically have a single circular chromosome.
Components: Each DNA strand is a polymer consisting of individual nucleotide monomers. A nucleotide comprises three essential components: a deoxyribose sugar, a phosphate group, and one of four nitrogenous bases.
Nitrogenous Bases: Adenine (A), Thymine (T), Cytosine (C), Guanine (G).
Historical Context of DNA Research
Friedrich Miescher (1869): While studying white blood cells, Miescher successfully isolated a novel acidic substance from the cell nuclei, which he termed 'nuclein.' This substance was later identified as DNA.
Early 19th and 20th century: Despite Miescher's discovery, the identification of DNA as the actual molecule responsible for heredity remained one of the most significant and perplexing biological challenges of this era. Proteins were widely believed to be the genetic material due to their greater complexity and diversity.
Transformation and Genetic Material
Transformation: This term refers to the remarkable phenomenon where a change in an organism's genotype (genetic makeup) and subsequently its phenotype (observable characteristics) occurs due to the assimilation of external DNA by a cell.
Frederick Griffith's Experiment (1928): Griffith's pioneering work with Streptococcus pneumoniae bacteria provided the first compelling evidence for genetic transformation. He demonstrated that:
Strain S (pathogenic): Possesses a smooth capsule, causing pneumonia in mice.
Strain R (non-pathogenic): Lacks a capsule, not causing disease in mice.
Results:
Live S bacteria injected into mice: Mice died.
Live R bacteria injected into mice: Mice lived.
Heat-killed S bacteria injected into mice: Mice lived.
Heat-killed S bacteria mixed with live R bacteria injected into mice: Mice died, and live S bacteria were recovered from the dead mice. This suggested a