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Questions and Answers

What is pyruvate converted into?

Acetyl coenzyme A

The citric acid cycle occurs in the cytoplasm.

False

What is the primary goal of the citric acid cycle?

To build electron acceptors to give to the electron transport chain

How many turns of the citric acid cycle are needed for 1 glucose molecule?

<p>2 turns</p> Signup and view all the answers

Oxidative phosphorylation generates ATP directly during the electron transport chain.

<p>False</p> Signup and view all the answers

What is produced when electrons are transferred in the electron transport chain?

<p>Water</p> Signup and view all the answers

Which phase is NOT part of mitosis?

<p>Interphase</p> Signup and view all the answers

What are the two types of cell division?

<p>Mitosis and meiosis</p> Signup and view all the answers

Binary fission is a method of asexual reproduction.

<p>True</p> Signup and view all the answers

What is the goal of meiosis?

<p>To produce four genetically distinct haploid cells</p> Signup and view all the answers

In humans, what is the total number of chromosomes?

<p>46</p> Signup and view all the answers

What do you call two identical alleles?

<p>Homozygous</p> Signup and view all the answers

Which allele determines the organism's appearance in a heterozygous condition?

<p>Dominant</p> Signup and view all the answers

What are Mendel's two laws of inheritance?

<p>Law of segregation and law of independent assortment</p> Signup and view all the answers

In a monohybrid cross of Yy x Yy, what is the probability of getting a green phenotype?

<p>25%</p> Signup and view all the answers

Probability of an event certain to occur is 0.

<p>False</p> Signup and view all the answers

What is the term for a cross that tests an unknown genotype with a recessive genotype?

<p>Test cross</p> Signup and view all the answers

Who is associated with the chromosomal theory of inheritance?

<p>Thomas Hunt Morgan</p> Signup and view all the answers

Which of the following describes sex-linked inheritance?

<p>Genes located on sex chromosomes</p> Signup and view all the answers

In humans, which sex chromosome pair is considered heterogametic?

<p>XY</p> Signup and view all the answers

What are neurons?

<p>Nerve cells</p> Signup and view all the answers

What is neuronal plasticity?

<p>Modifications in the brain after birth</p> Signup and view all the answers

What is short-term memory also known as?

<p>Working memory</p> Signup and view all the answers

Memory equals learning.

<p>False</p> Signup and view all the answers

What does LTP stand for?

<p>Long-term potentiation</p> Signup and view all the answers

What is the scientific method?

<p>A systematic approach for investigating phenomena</p> Signup and view all the answers

Which of these is part of the scientific method?

<p>All of the above</p> Signup and view all the answers

How many elements are essential to life?

<p>25</p> Signup and view all the answers

What is formed when the electronegativity difference between two atoms is less than two?

<p>Covalent bond</p> Signup and view all the answers

Ice sinks in water.

<p>False</p> Signup and view all the answers

The monomer of proteins is called a ______.

<p>amino acid</p> Signup and view all the answers

What are macromolecules formed from?

<p>Monomers</p> Signup and view all the answers

Which organic compound is known for storing energy?

<p>Lipids</p> Signup and view all the answers

What are the two classes of nucleic acids?

<p>DNA and RNA</p> Signup and view all the answers

What is the primary role of functional groups in organic molecules?

<p>Determine molecular function</p> Signup and view all the answers

In the context of the structure of a protein, what is denaturation?

<p>Loss of protein structure and function</p> Signup and view all the answers

What is the result of dehydration synthesis?

<p>Both B and C</p> Signup and view all the answers

What are the four main chemical building blocks of life?

<p>Carbon, Hydrogen, Oxygen, Nitrogen</p> Signup and view all the answers

How old is the Earth?

<p>4.6 billion years</p> Signup and view all the answers

When did life on Earth begin?

<p>About 3.5 billion years ago</p> Signup and view all the answers

Which hypothesis suggests life formed near the Earth's surface through spontaneous formation of monomers?

<p>Prebiotic soup hypothesis</p> Signup and view all the answers

Miller and Urey created life in a laboratory.

<p>False</p> Signup and view all the answers

What type of cells are prokaryotes?

<p>Bacteria and archaea</p> Signup and view all the answers

Which of the following is a common feature of eukaryotic cells?

<p>True nucleus</p> Signup and view all the answers

What process do prokaryotic cells use to divide?

<p>Binary fission</p> Signup and view all the answers

Which organelle is known as the 'powerhouse' of the cell?

<p>Mitochondria</p> Signup and view all the answers

All cells have ribosomes.

<p>True</p> Signup and view all the answers

What is the function of the Golgi apparatus?

<p>Modifies, sorts, and packages proteins</p> Signup and view all the answers

Define osmosis.

<p>Diffusion of water across a selectively permeable membrane</p> Signup and view all the answers

What term describes a solution that has a higher solute concentration outside the cell than inside?

<p>Hypertonic</p> Signup and view all the answers

Active transport does not require ATP.

<p>False</p> Signup and view all the answers

Cellular __________ is the process of engulfing large particles.

<p>phagocytosis</p> Signup and view all the answers

What is receptor mediated endocytosis?

<p>All of the above</p> Signup and view all the answers

What are metabolic pathways characterized by?

<p>They begin with a specific molecule and end with a product.</p> Signup and view all the answers

What is the function of catabolic pathways?

<p>Release energy</p> Signup and view all the answers

Anabolic pathways require energy.

<p>True</p> Signup and view all the answers

What is the first law of thermodynamics?

<p>Energy cannot be created nor destroyed, only converted.</p> Signup and view all the answers

What does Gibbs free energy indicate?

<p>The energy available to do work during a chemical reaction.</p> Signup and view all the answers

What happens if deltaG is less than zero?

<p>Energy is released from the reaction.</p> Signup and view all the answers

ATP drives endergonic reactions by phosphorylation.

<p>True</p> Signup and view all the answers

What do enzymes do?

<p>Enzymes speed up reactions by lowering energy barriers.</p> Signup and view all the answers

What is the result of denaturation in enzymes?

<p>It slows down or stops enzyme activity.</p> Signup and view all the answers

Match the following terms with their definitions:

<p>Oxidation = Loss of an electron Reduction = Gain of an electron OILRIG = Oxidation Is Losing Reduction Is Gaining Reducing agent = Electron donor</p> Signup and view all the answers

What is photosynthesis?

<p>The process by which photoautotrophs convert light energy into chemical energy.</p> Signup and view all the answers

What is the primary function of NADH in cellular respiration?

<p>To transfer electrons</p> Signup and view all the answers

What does glycolysis convert glucose into?

<p>2 pyruvates and 2 net ATP.</p> Signup and view all the answers

Study Notes

Long Term Potentiation

  • LTP is the encoding and re-encoding of memories, it is a physical change in the brain
  • LTP makes accessing a memory easier
  • It is a physiological change

Memory and Learning

  • Memory is not equal to learning
  • Learning is how we use memories to decrease the likelihood of negative outcomes
  • Learning is a form of natural selection
  • Learning can lead to a positive outcome

Using and Discarding Information

  • Information is sorted based on use
  • Information that is used is considered important, and retained
  • Information that is not used is considered unimportant, and discarded

Themes in Biology

  • Evolution is the core theme of biology, it explains the unity and diversity of organisms
  • Living organisms are modified descendants of a common ancestor
  • Emergent properties are properties that arise from the arrangement and interaction of parts within a system
  • Emergent properties demonstrate that the whole is more than just the sum of its parts

Levels of biological organization

  • Organelles are the functional units within cells
  • Cells are the fundamental unit of life
  • Tissues are groups of similar cells that perform a specific function
  • Organs are composed of different tissues that work together
  • Organ Systems are composed of different organs that work together
  • Organisms are individual living entities
  • Populations are groups of individuals of the same specie
  • Communities are groups of different populations living in the same area
  • Ecosystems are communities interacting with their surroundings
  • The Biosphere is a global ecosystem

Methods of Investigating Biology

  • The scientific method is a process for investigating and evaluating new knowledge
  • A hypothesis is a testable explanation for observations based on available data
  • A prediction is an expected outcome based on the hypothesis
  • A theory is a broad explanation that is well supported by evidence
  • A law is a statement of what always occurs under certain circumstances

Steps of the Scientific Method

  • Start with an observation of the world around you
  • Research background information on a topic
  • Formulate a hypothesis
  • Create a prediction based on the hypothesis
  • Design experiments to test the hypothesis
  • Evaluate the experiment based on the data

Chemistry

  • 25 out of 92 elements are essential to life
  • 4 elements make up 96% of matter: Oxygen, Carbon, Hydrogen, and Nitrogen
  • Atoms have 3 subatomic particles: protons, neutrons, and electrons
  • Electrons:
    • Have a negative charge
    • Move quickly
    • Determine how atoms interact
    • The further an electron is from the nucleus, the more potential energy it has
    • A more excited electron has more energy
  • Electron shells represent an electron's potential energy
  • Valance shells are the outermost shells and where chemical bonds form
  • Molecules are compounds that contain two or more atoms
  • Emergent properties of compounds often differ from their elements

Chemical Bonds

  • Electronegativity is an atom's affinity or tendency to attract electrons
  • Oxygen is strongly electronegative
  • The difference in electronegativity between two atoms determines the type of bond
  • Covalent bonds occur when the electronegativity between two atoms is less than 2
    • Sharing a pair of valence electrons between two atoms
    • Strong bonds within a cell
    • Non-polar covalent bonds occur when electronegativity is equal and the electrons are shared equally
    • Polar covalent bonds occur when there is an uneven sharing of electrons
  • Ionic bonds occur when the difference in electronegativity is greater than 2.
    • One atom steals an electron from the other
    • Forms between anions and cations
  • Weak Interactions in cells:
    • van der Waals interactions are weak attractions between close molecules that are caused by the movement of electrons
    • Hydrogen bonds are very strong dipole-dipole interactions

Emergent Properties of Water

  • Water is polar and forms hydrogen bonds with other water molecules
  • Cohesion is the ability of water molecules to stick together
  • Adhesion is the ability of water molecules to stick to other polar molecules
  • Surface tension is the measure of how hard it is to break the surface of a liquid
  • Water moderates temperature due to its high specific heat and high heat of vaporization
    • It takes a lot of energy to change temperatures
  • Water expands upon freezing due to its ordered hydrogen bonds
  • Water is a versatile solvent
    • Hydrophilic substances will dissolve in water (ions, salts, polar molecules)
    • Hydrophobic molecules will not dissolve in water (lipids, non-polar)

Importance of Carbon

  • Organic compounds contain carbon bonded to carbon or hydrogen
  • Carbon chains form the skeletons of organic molecules
  • Carbon:
    • Has 4 single valence electrons (tetravalent)
  • Structure is key to molecular function
  • Functional groups are chemical groups that are attached to carbon chains and alter molecular function, each functional group will have a different function
  • Hydrocarbons are made of carbon and hydrogen
    • Nonpolar and uncharged
    • Hydrophobic = insoluble in water

Functional Groups

  • There are 7 important functional groups:
    • Hydroxyl
    • Carbonyl
    • Carboxyl
    • Amino
    • Sulfhydryl
    • Phosphate
    • Methyl

Biological Macromolecules

  • Macromolecules are large complex molecules that are composed of smaller building blocks
  • Monomers are the building blocks of macromolecules
  • Polymers are chains of monomers
  • 3 out of 4 biological molecules are polymers:
    • Carbohydrates
    • Proteins
    • Nucleic acids
  • Lipids are biological molecules but not polymers
  • Monomers are joined together through dehydration synthesis, where water is removed
  • Monomers are broken apart by hydrolysis, where water is added
  • Enzymes called hydrolases are used to break down polymers
  • Intramolecular bonds are within molecules
  • Intermolecular bonds are between molecules

Carbohydrates

  • Carbohydrates mostly contain C, H, and O
  • The monomer is a sugar (monosaccharide), such as glucose (C6H12O6)
  • Carbohydrates are used for fueling and building materials
  • Glucose can exist in a linear or ring form - the ring form is more common
  • Covalent bonds between monosaccharides are called glycosidic linkages
  • Sucrose is a disaccharide composed of glucose and fructose
  • Polysaccharides are chains of sugar polymers
  • Structure and function of polysaccharides:
    • Starch (energy storage in plants)
    • Glycogen (energy storage in animals)
    • Cellulose (structural in plants)
    • Chitin (structural in animals)

Lipids

  • Lipids are not true polymers
  • They are hydrophobic and consist mostly of hydrocarbons
  • 3 families of lipids:
    • Fats
    • Phospholipids
    • Steroids
  • Fats:
    • Function is to store energy
    • Composed of a glycerol backbone and 1-3 fatty acids
    • Covalent bond between fatty acids and glycerol is called an ester linkage
    • Triglyceride is the storage form of fat
    • The presence of double bonds determines if a fatty acid is saturated, unsaturated or trans
      • Saturated fatty acids are found in animal fats and coconut oil, no double bonds
      • Unsaturated fatty acids are found in vegetable oils, have double bonds
      • Trans fats do not naturally occur
  • Phospholipids:
    • Found in cell membranes
    • Amphipathic meaning they have polar and non-polar regions
    • Glycerol and 2 fatty acids (hydrophobic)
    • Phosphate group on the 3rd carbon (hydrophilic)
    • Phospholipids form bilayers to form cell membrane
  • Steroids:
    • Composed of 3 rings of 6 carbons and 1 ring of 5 carbons
    • Side chains containing functional groups vary
    • Cholesterol in animals helps with communication and structural support in cell membranes
    • Cortisol is a stress hormone

Proteins

  • Proteins have many functions and structures
  • The monomer of a protein is an amino acid - there are 20 types
  • The polymer is a protein or polypeptide
  • The structure of an amino acid:
    • Amino group
    • Carboxyl group
    • Central carbon
    • Hydrogen (bonded to central carbon)
    • Variable "R" group
  • R groups determine polarity, function, and acidity.
  • Peptide bonds form between amino acids

Protein Structure

  • A polypeptide is a chain of amino acids
  • Each amino acid in a polypeptide is joined together by a peptide bond, but to become a functional protein, the polypeptide must be folded into the correct 3D shape
  • 4 levels of protein structure:
    • Primary structure:
      • The sequence of amino acids in a polypeptide chain joined by peptide bonds
    • Secondary structure:
      • Interactions within the polypeptide chains
      • Hydrogen bonds between amino acids
      • R-groups do not participate
      • Secondary structures form helices (coils) and pleated sheets
    • Tertiary structure:
      • Interactions within the polypeptide chain
      • R-groups interact to fold into a specific 3D shape
      • All types of bonds (hydrogen, ionic, hydrophobic)
    • Quaternary structure:
      • Multiple polypeptide chains form a macromolecule (no more folding)
  • Denaturation is when the 3D shape of a protein is disrupted
    • A denatured protein is biologically inactive
    • Denaturation can be caused by pH, salt concentration, or changes in temperature

Nucleic Acids

  • Monomers are nucleotides
  • Two classes:
    • DNA (deoxyribonucleic acid)
    • RNA (ribonucleic acid)
  • Nucleic acids transmit hereditary information and determine protein production
  • Monomers are held together by phosphodiester bonds

Origin of Life

  • Abiogenesis is the theory that life arose from non-living matter
  • 4 main steps of abiogenesis:
    • Abiotic synthesis of monomers
    • Synthesis of macromolecules
    • Formation of protocells
    • Appearance of self-replication
  • Abiotic Synthesis of monomers:
    • Early earth was an oxygen-free environment
    • Oxygen breaks bonds (oxidizes)
    • A source of energy was needed to build biological molecules
    • Needed the presence of chemical building blocks (CHON) (in the form of water, dissolved inorganic minerals, and atmospheric chemicals)
    • Time was needed for the molecules to react
    • Earth is 4.6 billion years old, and life started about 3.5 billion years ago
    • Prebiotic soup hypothesis: life formed near earth's surface and monomers spontaneously formed
      • Miller-Urey Experiment in 1953 tested the hypothesis
        • They formed amino acids and other organic molecules
        • They did not create life in a lab, they demonstrated that monomers can be created from non-living matter
    • Iron-sulfur world hypothesis: life formed at cracks in the ocean floor (hydrothermal vents)
      • H2O. CO, and other minerals released from vents
      • Iron was a catalyst for building molecules
  • Synthesis of Macromolecules
    • Polymers formed from monomers (proteins or RNA)
    • Monomers polymerized on hot sand and rock
    • Negative ions bound monomers together
  • Formation of Protocells
    • Lipid membranes spontaneously formed vesicles (containers)
    • Organic polymers exhibited attributes of living cells:
      • Osmosis
      • Homeostasis
      • Division
    • No mechanism of heredity
  • Appearance of Self-Replication
    • RNA was the nucleic acid in protocells
    • RNA is capable of self-replication and catalyzing protein synthesis (Ribozymes)
    • DNA evolved later and is:
      • Double stranded
      • More stable

History of Life

  • 3.5 billion years ago - prokaryotes
  • All bacteria were heterotrophic
  • First heterotrophs were fermentative (anaerobic)
  • Photosynthetic autotrophs appeared - used energy from sunlight and released O2
  • Rise of atmospheric oxygen led to the evolution of aerobic bacteria
  • Archaea arose from aerobic bacteria
  • Eukarya arose from archaea and bacteria
  • A symbiotic relationship existed
  • Endosymbiont theory:
    • Mitochondria and chloroplasts were bacteria
  • Oldest fossils: 1.8 billion years old

Key events In History of Life

  • Abiotic synthesis of monomers under early earth conditions
  • Abiogenesis: Monomers -> polymers -> protocells -> self-replication (life)
  • Heterotrophic anaerobic bacteria
  • Photosynthetic bacteria (atmospheric O2)
  • Archaea
  • Endosymbiosis: leads to eukarya

Cellular Diversity

  • Classified by structure and morphology
  • Prokaryotic cells: bacteria and archaea
    • No membrane bound organelles
    • Smaller than eukaryotic cells
    • Usually unicellular
    • Have ribosomes
    • Have a cell wall (not made of cellulose)
    • Have a plasma membrane
    • Most have a capsule (sticky outer layer)
    • Have flagella (hair-like projections)
    • Have pili (hair-like projections)
  • Eukaryotic cells: protists, fungi, plants, and animals
    • Membrane bound organelles
    • 10 times larger than prokaryotic cells
    • Usually multicellular with a few exceptions
    • Have ribosomes
    • Most have a plasma membrane
    • Have cytoplasm
    • Have a cytoskeleton
    • Some have a cell wall
    • Include a nucleus:
      • Contains the cell's genetic material (DNA)
      • Controls the cell's activities
    • Endoplasmic Reticulum:
      • A network of membranes that transport proteins throughout the cell
      • Rough ER is covered in ribosomes, makes and modifies proteins
      • Smooth ER synthesizes lipids and metabolizes carbohydrates
    • Golgi apparatus:
      • Modifies, sorts, and packages proteins that come from the ER
      • Flattened sacs of membranes
    • Lysosomes:
      • Cellular digestion
    • Vacuoles
      • Storage and transport of waste products and water
    • Mitochondria
      • Creates the energy of the cell (ATP) through cellular respiration

Cell Structure

  • The plasma membrane is the outer cell boundary
    • Selectively permeable barrier
    • Phospholipid bilayer
    • Has embedded proteins
    • Helps with cell communication
    • Regulates what goes in and out of the cell
    • Maintains cell shape
  • Cell wall provides structural support and protection outside the plasma membrane
  • Cytoplasm is the gel-like substance that fills the cell
    • Contains many of the cell's organelles and is where many metabolic reactions occur
  • The cytoskeleton is a network of fibers that provides structural support, aids in movement, and helps with organization in the cell
    • Microtubules: responsible for cell structure, movement of organelles, and flagella and cilia formation
    • Microfilaments: responsible for movement, changes in cell shape, and muscle contractions
    • Intermediate filaments: provide structural support, anchor organelles, and form nuclear lamina
  • Centrioles are involved in cell division and microtubule formation
  • Ribosomes are responsible for protein synthesis
    • Made of two subunits that join to mRNA
    • Two types:
      • Free ribosomes - make proteins for the cell
      • Bound ribosomes - make membrane bound proteins that are exported from the cell
  • The nucleus houses the genetic material of the cell
    • Contains DNA
    • Controls cellular function
    • Nuclear envelope is a double membrane containing pores
    • Nucleolus is a dark stained region of the nucleus where rRNA is produced

Cell Structure and Function

  • Prokaryotic cells
    • Size: 1-10 micrometers
    • Nucleus: Absent. DNA is in a nucleoid region (not membrane-bound)
    • DNA: Circular, single stranded
    • Ribosomes: Located in the cytosol
    • Organelles: Absent
    • Other components: Plasma membrane, cell wall
    • Division: Binary fission
  • Eukaryotic cells
    • Size: 10–100 micrometers
    • Nucleus: Present. DNA is in linear chromosomes inside the nucleus
    • Organelles: Mitochondria, chloroplasts, endomembrane system, Golgi apparatus, lysosomes, vacuoles
    • Ribosomes: Found in the cytosol or bound to the endoplasmic reticulum (ER)
    • Cell wall: Present in some cells, not all
    • Division: Mitosis

Common Features of Cells

  • Smallest unit of life
  • Multicellular organisms: Composed of specialized, cooperative cells
  • Cell theory:
    • All living organisms are made of cells
    • All cells have four common features: plasma membrane, cytosol, chromosomes, and ribosomes
    • All cells have a common evolutionary ancestor
  • Basic cell structure:
    • Plasma membrane: Phospholipid bilayer that selectively controls what enters and exits the cell
    • Cytosol/cytoplasm: Semifluid substance that fills the cell
    • Chromosomes: Carry genes and are made of DNA
    • Ribosomes: Synthesize polypeptide chains and are made of RNA
  • Cell size:
    • Small size is due to the surface area to volume ratio. Larger cells have a smaller ratio, making it difficult for them to get nutrients in and waste out
    • Larger organisms compensate for this by having specialized compartments (organelles) or being multicellular

Eukaryotic Cell Components

  • Nucleus:
    • Structure: Surrounded by the nuclear envelope, which is a double membrane.
    • Inside: Contains DNA organized into linear chromosomes, nucleolus (site of ribosome synthesis), RNA, and proteins.
    • Nuclear envelope:
      • Two membranes, both lipid bilayers
      • Interior is connected by the nuclear lamina (a protein network)
      • Maintains the shape of the nucleus
      • Regulates transport in and out of the nucleus through nuclear pores
  • Mitochondria and chloroplasts:
    • Theory of endosymbiosis: Both mitochondria and chloroplasts have a double membrane, their own DNA and ribosomes. They replicate by binary fission and are hypothesized to have originated from prokaryotic cells that were absorbed by a larger cell.
  • Ribosomes:
    • Found in all cells
    • Structure: Non-membrane bound (not an organelle), composed of ribosomal RNA (rRNA) and proteins
    • Function: Involved in the synthesis of polypeptide chains.
      • Free ribosomes: Found in all cells.
      • Bound ribosomes: Attached to the endoplasmic reticulum (ER).
  • Endomembrane system:
    • A network of intracellular membranes composed of phospholipid bilayers that separate the cell’s interior from the exterior.
    • Structure:
      • Continuous: One long structure
      • Connected via vesicles: Transfer membrane segments to other parts of the system
    • Function:
      • Regulates the folding and movement of proteins
      • Performs metabolic functions
  • Plasma membrane:
    • All cells have one. Encloses the cell contents but isn’t equal to a cell wall
    • Selectively permeable: Regulates what and how much gets in and out of the cell
  • Nuclear envelope:
    • Encloses DNA
    • Messenger RNA (mRNA) is synthesized from DNA, leaves through nuclear pores, and then travels to the cytoplasm
  • Endoplasmic reticulum (ER):
    • Connected to the nuclear envelope
    • Two regions:
      • Smooth ER:
        • Lacks ribosomes
        • Function: synthesizes lipids, metabolizes carbohydrates, detoxifies drugs and poisons, and stores calcium ions
      • Rough ER:
        • Has ribosomes attached
        • Function: Synthesizes proteins, folds and modifies them, secretes glycoproteins, distributes transport vesicles, serves as a cell membrane factory
  • Golgi apparatus:
    • Structure: Stacks of membranous sacs called cisternae. Not continuous with the ER
    • Cis face: “Receiving” side of the ER
    • Trans face: “Shipping” side
    • Function: Modifies ER products, sorts and packages them, manufactures macromolecules, and ships products using transport vesicles
  • Lysosomes:
    • “Cell stomach”
    • Sacs of hydrolytic enzymes
    • Primary lysosome: Buds off the Golgi. Does not contain food
    • Food enters in a vacuole -> fuses with lysosome -> forms a secondary lysosome
    • Secondary lysosome: Responsible for breaking down complex molecules
  • Vacuoles:
    • Membrane-bound containers derived from the ER and Golgi apparatus
    • Function:
      • Food vacuoles: Store food
      • Contractile vacuoles: Pump out water
      • Central vacuoles: Hold water in plant cells

Membrane Structure

  • Phospholipid bilayer: Forms spontaneously due to the amphipathic nature of phospholipids. The polar head groups are hydrophilic and face the outside of the membrane, while the non-polar tails are hydrophobic and face the inside of the membrane.
  • Membrane proteins: Determine many membrane functions, can move laterally, can’t flip.
    • Integral proteins: Span the entire membrane. These are amphipathic
    • Peripheral proteins: Can be polar or non-polar and don’t span the entire membrane
  • Membrane protein functions:
    • Transport
    • Enzymes
    • Signal transduction
    • Other functions: Cell-cell recognition, intercellular joining, attachment to the cytoskeleton and extracellular matrix (ECM)
  • Carbohydrates:
    • Polysaccharides attached to proteins (glycoproteins) or lipids (glycolipids)
    • Function: Used for cell identification (ex. determining blood types)
  • The fluid mosaic model: Describes the structure of the plasma membrane as a fluid, constantly moving mosaic of lipids, proteins, and carbohydrates.
    • Fluidity is affected by: Temperature, length of tails, bends in tails (saturation), and amounts of cholesterol. Cholesterol acts as a spacer
  • Plasma membrane:
    • Selectively permeable
    • Two basic types of transport:
      • Passive transport: Movement of molecules across the membrane without the use of metabolic energy (ATP). Moves down the concentration gradient.
      • Active transport: Movement of molecules across the membrane that requires metabolic energy (ATP). Moves against the concentration gradient.

Membrane Transport

  • Passive transport:
    • Simple diffusion: Movement of molecules down a concentration gradient without the assistance of proteins.
    • Osmosis: Diffusion of water across a selectively permeable membrane, usually from a region of lower solute concentration to a region of higher solute concentration.
    • Facilitated diffusion: Movement of molecules down a concentration gradient with the assistance of transport proteins.
  • Net movement: Passive transport always occurs down the concentration gradient until dynamic equilibrium is reached.
  • No ATP required
  • Diffusion: The tendency of molecules to move from areas of high concentration to low concentration.
    • Small gases (O2, CO2, N2) diffuse easily.
    • Small non-polar molecules
    • Small polar uncharged molecules (e.g. H2O)
  • Osmosis:
    • Tonicity: The ability of a solution to cause a cell to gain or lose water
    • Isotonic solution: Equal solute concentration inside and outside the cell
    • Hypertonic solution: Higher concentration of solute outside the cell. The cell will lose water.
    • Hypotonic solution: Lower concentration of solute outside the cell. The cell will gain water.
  • Facilitated diffusion:
    • Movement of large molecules or ions, like H+, Ca^2+, Na+
    • Requires transport proteins (integral proteins)
  • Active transport:
    • Moves against the gradient
    • Requires ATP
    • Can be facilitated by proteins (carriers or pumps) or bulk transport.
    • Carriers/pumps: Integral membrane proteins that change shape to help transport molecules
    • Bulk transport: Large numbers of molecules are transported at once.
      • Not carrier-mediated
      • Formation of vesicles
  • Active transport always requires ATP
  • Doesn’t pass through the plasma membrane

Bulk Transport

  • Exocytosis: Process by which cells release waste, proteins, and secretory products.
    • Step 1: Vesicles fuse with the plasma membrane
    • Step 2: Contents are released from the cell
    • Vesicle fusion with the plasma membrane is the primary mechanism for cell membrane growth
  • Endocytosis: Process by which cells take in material by forming vesicles derived from the plasma membrane.
    • Three types:
      • Phagocytosis: "Cellular eating"
        • Cell engulfs large particles
        • Non-specific
      • Pinocytosis: "Cellular drinking"
        • Ingestion of fluid and dissolved material
        • Non-specific
      • Receptor-mediated endocytosis:
        • Receptor proteins in the plasma membrane bind specific macromolecules outside the cell
        • Form coated pits
        • Fold inward to form vesicles.
        • The main mechanism for the uptake of macromolecules.
        • Specific

Metabolism and Energy Change

  • Metabolism: The sum of all chemical reactions that occur in a living organism.
    • Metabolic pathways:
      • Begin with a specific molecule and end with a product
      • Each step is catalyzed by a specific enzyme
  • Catabolic pathways:
    • Break down complex molecules into simpler ones
    • Release energy
    • Ex: cellular respiration
  • Anabolic pathways:
    • Build complex molecules from simpler ones
    • Require energy
    • Ex: synthesis of protein from amino acids
  • Free-energy change: The amount of energy available to do work in a chemical reaction.
    • Energy: The capacity to cause change or do work
    • Kinetic energy: Energy of motion
    • Potential energy: Stored energy
    • Thermodynamics: The study of energy transformations
      • First law of thermodynamics: Energy cannot be created or destroyed, only converted.
      • Second law of thermodynamics: Every energy transformation increases entropy (disorder).
    • Entropy: A measure of disorder
      • The more energy a system loses to its surrounding, the less ordered and more random the system becomes
    • Light energy: Enters an ecosystem, and heat energy exits the ecosystem.
    • Energy conversion: Never 100% efficient
    • Total energy in the universe: Constant
    • Gibbs free energy: Energy available to do work
      • Delta G: The change in Gibbs free energy
        • Delta G < 0: Energy is released (exergonic reaction, spontaneous)
        • Delta G = 0: Chemical process is at equilibrium
        • Delta G > 0: Energy is required (endergonic reaction, nonspontaneous)
  • ATP: Adenosine triphosphate. The cell’s primary energy currency.
    • Structure: Ribose (5-carbon sugar), adenine (nitrogenous base), 3 phosphate groups
    • Coupled reactions: Pairing of an exergonic reaction to provide energy for an endergonic reaction
      • Hydrolysis of ATP: Is exergonic
      • ATP drives endergonic reactions by phosphorylation: Transfer of a phosphate group to another molecule, changing the molecule’s shape, making it a phosphorylated intermediate
      • Phosphorylation of a reactant: A phosphate group binds to a protein or reactant, causing a change in shape or function
      • Hydrolysis of ATP: Results in ADP (adenosine diphosphate) and P (inorganic phosphate).

Enzymes

  • Enzymes: Catalysts that speed up reactions by lowering the activation energy (the initial energy required to start a reaction).
  • Active site: A cleft or groove on the enzyme where the substrate binds
  • Substrate: The reactant that an enzyme acts upon
  • Change in shape: Facilitates the breaking of bonds
  • Factors affecting enzyme activity:
    • Temperature and pH: Enzymes have an optimal temperature and pH.
      • Human optimal temperature: 35-40 degrees Celsius
    • Denaturation: At high temperatures, even short exposure can denature enzymes (lose their shape and function). At low temperatures, enzymes function slowly or not at all.
    • Enzyme helpers:
      • Cofactors: Inorganic (often metals like iron or zinc)
      • Coenzymes: Organic (e.g. NAD+ and FAD+, vitamins)
    • Inhibition:
      • Competitive inhibition: Inhibitors bind to the active site and compete with the substrate (e.g. penicillin)
      • Noncompetitive inhibition: Inhibitors bind to a different part of the enzyme and cause a change in shape of the active site (e.g. cyanide)

Redox Reactions

  • Redox reactions: Reactions that involve the transfer of electrons.
    • Oxidation: Loss of electrons
    • Reduction: Gain of electrons
    • Electron carrier molecules: Molecules that transport electrons from one reaction to another (e.g. NAD+ and FAD+)
  • Importance: Redox reactions are essential for many metabolic processes, including cellular respiration and photosynthesis.

Redox Reactions

  • Redox reactions involve the transfer of electrons between reactants.
  • Oxidation is the loss of one or more electrons by a molecule, and the molecule is said to be oxidized.
  • Reduction is the gain of electrons by a molecule, and the molecule is said to be reduced.
  • OILRIG serves as an acronym for remembering the concepts: Oxidation Is Losing Reduction Is Gaining
  • A reducing agent donates electrons and is oxidized in a redox reaction.
    • It often loses a hydrogen atom (H+) during this process.
    • For example, NADH (nicotinamide adenine dinucleotide) is oxidized to NAD+ by losing a hydrogen atom (and an electron).
    • NADH is the reducing agent.
  • An oxidizing agent accepts electrons and is reduced in a redox reaction.
    • It often gains a hydrogen atom (H+) during this process.
    • For example, NAD+ is reduced to NADH by gaining a hydrogen atom (and an electron).
    • NAD+ is the oxidizing agent.

Photosynthesis

  • Photosynthesis is an endergonic process, requiring an input of energy.
  • It is driven by light energy, which is a form of electromagnetic radiation.
  • Light travels as waves and is composed of small particles of light energy called photons.
  • Shorter wavelengths of light have more energy per photon, while longer wavelengths carry less energy.
  • When a molecule absorbs a photon of light, it becomes energized, and an electron within the molecule can shift to a higher energy level.
  • The energized electron can either return to its lower energy state or leave the atom and be captured by an electron acceptor, reducing the acceptor molecule.
  • Chlorophyll is a green pigment found in chloroplasts, which are photosynthetic organelles in plants.
  • Chlorophyll absorbs light energy, giving plants their green color because they reflect and transmit green wavelengths.
  • Chloroplasts have a double membrane structure and contain internal stacks of membranous sacs called thylakoids.

Photosynthetic Pigments

  • Chlorophyll is a photosynthetic pigment that absorbs visible light.
  • It is embedded within the thylakoid membrane.

Process of Photosynthesis

  • Photosynthesis is an endergonic reaction with a positive change in Gibbs free energy (+deltaG).
  • The light-dependent reactions take place within the thylakoids of chloroplasts.
    • They involve the splitting of water molecules, releasing oxygen (O2).
    • They also reduce NADP+ to NADPH and generate ATP from ADP, which are used in the Calvin cycle.
  • The two photosystems (PSII and PSI) are involved in the light-dependent reactions.
    • They capture sunlight and transform it into chemical energy in the form of ATP and NADPH.
  • The majority of reactions in photosynthesis utilize linear electron flow.
    • Linear electron flow begins with PSII and proceeds to PSI, generating ATP, NADPH, and O2.
  • The older, pre-oxygen revolution process involves cyclic electron flow, which only produces ATP.
  • Photosystems consist of light-harvesting complexes and a reaction center.
    • The reaction center contains a specific pigment molecule (P680 in PSII and P700 in PSI).
  • Two electron transport chains (ETC) are involved in photosynthesis.
    • The PSII ETC uses electrons to pump H+ ions into the thylakoid lumen, creating a proton gradient.
    • The PSI ETC catalyzes the creation of NADPH.
  • ATP synthase is a protein complex that facilitates the flow of protons (H+) across the thylakoid membrane. This flow drives the phosphorylation of ADP to ATP.

Light-Dependent Reactions: Linear Electron Flow

  • Both photosystems participate in linear electron flow.
  • Three key processes occur in each photosystem:
    • An electron is excited by light energy.
    • The energy of the excited electron is used to perform work.
    • The electron is replaced to continue the process.
  • Several steps involve redox reactions.
    • In PSII, the P680 pigment is energized, becoming P680+.
    • The P680+ then oxidizes the primary electron acceptor, which is a redox reaction.
    • The energy of the electron is used to drive proton pumping in the ETC, ultimately leading to ATP synthesis.
    • The electron lost by P680 is replaced when water is split, releasing oxygen as a byproduct.
  • In PSI, light energy excites the P700 pigment, oxidizing it to P700+.
  • The electron from the PSII ETC is then replaced in PSI, which is then used by NADP+ reductase to produce NADPH.

Carbon Fixation Reactions

  • The carbon fixation reactions occur in the stroma of chloroplasts.
  • The Calvin cycle, consisting of three stages, is responsible for reducing carbon dioxide (CO2) to sugar using NADPH and ATP.
  • The three stages of the Calvin cycle are:
    • Carbon Fixation: CO2 combines with RuBP (ribulose bisphosphate) catalyzed by RuBisCo, forming PGA (phosphoglycerate).
    • Carbon Reduction: PGA is converted to G3P (glyceraldehyde-3-phosphate) using ATP and NADPH.
    • Regeneration: 5 molecules of G3P are rearranged to regenerate 3 molecules of RuBP.

Cellular Respiration

  • Cellular respiration is a series of redox reactions that convert energy stored in glucose into energy within the form of ATP.
  • These reactions occur in both the cytosol and mitochondria of eukaryotic cells.
  • Cellular respiration oxidizes glucose to produce a significant amount of ATP, using a series of electron carriers.
  • NAD+ and FAD are important electron carriers in respiration.
  • NADH and FADH2 are reduced forms of these electron carriers, storing energy for ATP production.

Stages of Cellular Respiration

  • Glycolysis occurs in the cytosol of the cell.
    • It converts glucose into two molecules of pyruvate, producing a net gain of 2 ATP molecules.
    • Glycolysis proceeds through two main stages: an energy investment phase, where 2 ATP are used, and an energy payoff phase, where 4 ATP and 2 NADH are produced.
    • Glycolysis does not require oxygen and occurs in the cytoplasm.
  • Pyruvate Oxidation occurs in the mitochondria.
    • Each pyruvate is converted into acetyl-CoA, a two-carbon molecule that enters the citric acid cycle.
    • In this process, NAD+ is reduced to NADH.
    • Pyruvate oxidation does not generate ATP.
  • Citric Acid Cycle (CAC) takes place in the mitochondrial matrix.
    • Acetyl-CoA combines with oxaloacetate, an organic molecule, initiating the cycle.
    • The cycle generates ATP, NADH, FADH2, and CO2.
  • Oxidative Phosphorylation occurs in the inner mitochondrial membrane, specifically the cristae.
    • This process harnesses the energy stored in NADH and FADH2 to produce ATP.
  • Chemiosmosis is a vital part of oxidative phosphorylation that utilizes a proton gradient to drive ATP synthesis.

Electron Transport Chain (ETC)

  • The ETC is a series of protein complexes embedded in the inner mitochondrial membrane.
  • Electrons from NADH and FADH2 are passed along this chain.
  • As the electrons move through the chain, the energy released from their transfer pumps protons (H+) from the mitochondrial matrix to the intermembrane space.
  • This process creates a proton gradient, which is used by ATP synthase to generate ATP.
  • Oxygen is the final electron acceptor in the ETC.
  • When oxygen accepts electrons, it combines with protons to form water.

ATP synthase

  • ATP synthase is a molecular mill that exploits the proton gradient created by the ETC.
  • Protons (H+) flow back through ATP synthase from the intermembrane space to the matrix, driving the rotation of a component within the protein.
  • This rotational movement allows ATP synthase to catalyze the phosphorylation of ADP to ATP.

Cellular Respiration: Summary

  • Glycolysis breaks glucose into pyruvate.
  • Pyruvate is oxidized to acetyl-CoA, which enters the citric acid cycle.
  • The citric acid cycle fully oxidizes acetyl-CoA, producing electron carriers like NADH and FADH2.
  • The ETC utilizes the energy in the electron carriers to create a proton gradient that powers ATP synthesis via chemiosmosis.

Binary Fission

  • Binary fission is a type of asexual reproduction common in prokaryotes.
  • The organism replicates its DNA and divides into two identical daughter cells.
  • It is a simple process due to prokaryotes' lack of a nucleus and presence of a single circular chromosome.

Cell Cycle

  • The cell cycle is a series of events that lead to the growth and division of a cell.
  • It is essential for reproduction, growth, and development, as well as tissue repair.
  • The eukaryotic cell cycle consists of two phases:
    • Interphase, where the cell prepares for division, and
    • M (mitotic) phase, where the cell divides.

Organization of Genetic Material

  • The genome encompasses all the DNA within a cell, containing the genetic instructions for the organism.
  • Prokaryotes have a single circular DNA molecule, while eukaryotic cells contain several linear DNA molecules.
  • In eukaryotic cells, DNA is associated with proteins forming chromatin, which condenses into chromosomes during cell division.
  • Humans have 46 chromosomes in their somatic cells, with each chromosome duplicated to form sister chromatids during the S phase of the cell cycle.
  • The centromere, a pinched region, holds sister chromatids together.
  • Kinetochores are protein structures that attach to the centromere and serve as attachment points for microtubules during mitosis.

Phases of the Cell Cycle

  • Interphase is a period of growth and DNA replication.

    • It includes three subphases:

  • G1 phase: The cell grows and performs normal functions.

  • S phase: DNA replication occurs, doubling the amount of genetic material.

  • G2 phase: The cell prepares for mitosis, producing necessary proteins and organelles.

  • Mitotic Phase: This phase involves both mitosis, nuclear division, and cytokinesis, the division of the cytoplasm.

Events of Interphase

  • G1 phase is the longest phase of the cell cycle, representing about 90% of a cell's life.
    • DNA is not synthesized, and the cell focuses on growth, normal functions, and protein production.
  • S phase is when DNA replication takes place.
    • Each chromosome is duplicated, forming sister chromatids connected at the centromere.
    • The ploidy of the cell remains the same (2n  2n), but the amount of genetic material doubles.
  • G2 phase is the time when the cell prepares for mitosis.
    • Critical proteins and organelles required for cell division are produced.

G2 phase

  • Centrosomes duplicate during G2 phase.
  • Each centrosome contains two centrioles.
  • The centrosomes play a crucial role in the formation of the mitotic spindle, which is essential for chromosome segregation during cell division.

M phase

  • M phase consists of Mitosis and Cytokinesis, which are necessary for a single cell to divide into two daughter cells.
  • Mitosis is further divided into four stages: prophase, metaphase, anaphase, and telophase.
  • Cytokinesis is the division of the cytoplasm, which occurs after mitosis.

Prophase

  • During prophase, chromosomes condense, becoming visible under a microscope.
  • The mitotic spindle forms, extending from the centrosomes, which migrate to opposite poles of the cell.
  • The nuclear envelope breaks down, allowing the spindle fibers to interact with chromosomes.
  • Spindle fibers attach to the kinetochore of each chromosome, which are protein structures on the centromere.

Metaphase

  • The longest stage of mitosis.
  • Chromosomes align along the metaphase plate (a plane equidistant from the two poles of the spindle).

Anaphase

  • The shortest stage of mitosis.
  • Cohesion proteins holding sister chromatids together are cleaved by an enzyme, allowing the sister chromatids to separate.
  • Sister chromatids are pulled toward opposite poles of the cell.
  • Each pole receives a complete set of chromosomes.

Telophase

  • Two new daughter cells begin to form.
  • The nuclear envelope reforms around the chromosomes at each pole.
  • Cytokinesis typically starts during telophase.

Cytokinesis

  • Not a part of mitosis, but overlaps with its final stages.
  • Cytoplasm is divided, forming two distinct daughter cells.
  • In animal cells, cytokinesis involves a cleavage furrow, constricting the cell membrane from the outside.
  • In plant cells, cytokinesis involves the formation of a cell plate in the middle of the dividing cell.
  • Each daughter cell inherits a complete set of chromosomes, organelles, and an appropriate amount of cytoplasm.

Introduction to heredity

  • Heredity is the passing of traits from parents to offspring.
  • Reproduction can be either asexual or sexual.

Asexual reproduction

  • One parent produces offspring.
  • Involves mitosis.
  • Results in genetically identical clones.
  • Advantages of asexual reproduction include speed and consistency.
  • Disadvantages of asexual reproduction include a lack of genetic variation, making them vulnerable to environmental changes.

Sexual reproduction

  • Two parents contribute genetic material to offspring.
  • Involves meiosis.
  • Produces offspring with a unique combination of genetic material.
  • Advantages of sexual reproduction include increased genetic variation, allowing for adaptation to changing environments.
  • Disadvantages of sexual reproduction include the need to find a mate and slower reproduction time.

Types of chromosomes

  • Somatic cells are diploid (2n), containing pairs of chromosomes called homologous chromosomes.
  • Humans have 46 chromosomes, organized into 23 pairs of homologous chromosomes.
  • One pair is sex chromosome (XX or XY).
  • The remaining 22 pairs are autosomes, which control traits other than gender.
  • Gametes are haploid (n) cells produced through meiosis, containing only one set of chromosomes (23 chromosomes in humans).

Life cycles of different organisms

  • A life cycle describes the stages from conception to the production of offspring.

Human life cycle

  • Life cycle involves fertilization and meiosis.
  • These processes ensure that offspring inherit the appropriate number of chromosomes.
  • Haploid and diploid stages alternate throughout the life cycle.

Fertilization

  • The fusion of a haploid sperm cell and a haploid egg cell, resulting in a diploid zygote (2n).
  • The zygote develops into a multicellular organism.

Meiosis

  • Cell division that reduces the number of chromosomes from diploid (2n) to haploid (n), producing gametes.
  • Ensures each gamete (egg or sperm) receives only one chromosome from each homologous pair.

Three types of sexual life cycles

  • Plants, fungi, and many protists exhibit different life cycles.
  • Plants have an alternation of generations, with both haploid and diploid multicellular stages.
  • Fungi and many protists have a dominant haploid stage.

Meiosis

  • A type of cell division that produces four haploid daughter cells from a single diploid cell.
  • Each daughter cell is genetically unique, contributing to genetic variation.

Stages of meiosis

  • DNA replication occurs before meiosis begins, ensuring each chromosome consists of two sister chromatids.
  • Meiosis is divided into two main phases: Meiosis I and Meiosis II.

Interphase

  • Similar to the interphase in mitosis: consisting of G1, S, and G2 phases.
  • During the S phase, chromosomes replicate.
  • In the G2 phase, centrioles replicate.

Meiosis I

  • Separates homologous chromosomes, reducing the ploidy from diploid (2n) to haploid (n).

Prophase I

  • The longest stage of meiosis.
  • Chromosomes condense.
  • Homologous chromosomes pair up, aligning by gene, forming tetrads (four sister chromatids).
  • Synapsis is the process by which homologous chromosomes pair up.
  • Crossing over occurs between non-sister chromatids, exchanging genetic material.
  • Chiasmata are the points where crossing over occurs.
  • Crossing over increases genetic diversity.

Metaphase I

  • Homologous chromosome pairs line up at the metaphase plate.
  • Alignment of homologous chromosomes is random, contributing to genetic variation.

Anaphase I

  • Homologous chromosomes separate (disjunction), with sister chromatids remaining attached.
  • The ploidy of the cell is effectively halved.

Telophase I and Cytokinesis

  • Chromosomes, each consisting of sister chromatids, are moved to opposite poles of the cell.
  • Cytokinesis typically occurs simultaneously with telophase I.

Interkinesis

  • A brief pause between meiosis I and meiosis II.
  • No chromosome replication occurs during interkinesis.

Meiosis II

  • The second phase of meiosis, similar to mitosis in terms of the stages.

Prophase II

  • The spindle forms, and the nuclear envelope breaks down.
  • No crossing over occurs in Prophase II.

Metaphase II

  • Sister chromatids align at the metaphase plate.

Anaphase II

  • Sister chromatids separate, creating individual chromosomes.
  • No change in ploidy occurs during Anaphase II.

Telophase II and Cytokinesis

  • Chromosomes arrive at opposite poles of the cell.
  • Cytokinesis follows, resulting in four haploid daughter cells, each genetically different.

Mendel's Experiments

  • Gregor Mendel (1822-1884) studied the inheritance of traits in pea plants, which became an important model system for understanding genetics.

Mendel’s Experimental Approach

  • Pea plants have several advantages for genetic studies:
    • Easy to grow and manipulate pollination.
    • Many distinct varieties with easily identifiable traits.
    • Produce numerous offspring.
  • Mendel’s experiments disproved the blending hypothesis, which suggested that traits from the parents would mix like fluids.
  • Instead, Mendel proposed the particulate inheritance model, suggesting that heritable factors (genes) determine traits.
  • Each character in an organism is controlled by two factors (alleles), one from each parent.

Mendel's Model

  • Mendel's model of particulate inheritance has four key concepts:

    • Alleles: Alternative versions of a gene (e.g., different alleles for seed color). Typically, diploid organisms have two alleles for each gene.
    • Two alleles: Individuals inherit one allele from each parent.
    • Dominant and recessive alleles: Dominant alleles determine the organism's appearance even if a recessive allele is also present. Recessive alleles only affect the phenotype when paired with another recessive allele.
    • Mendel's Laws:
      • Law of segregation: Individuals inherit two copies of each gene (alleles), and during gamete formation, each gamete receives only one allele.
      • Law of independent assortment: Genes on different chromosomes are inherited independently of each other, meaning that the inheritance of one gene does not influence the inheritance of another gene.

Genetic crosses

  • Punnett squares are helpful tools to predict the genotypes and phenotypes of offspring from crosses between parents with known genotypes.
  • A phenotype describes the physical expression of a trait, while a genotype describes the genetic makeup for a trait.
  • A monohybrid cross involves one character.
    • Crossing two homozygous parents with different alleles (e.g., homozygous yellow and homozygous green) results in F1 offspring that are all heterozygous.
    • The F1 generation, although expressing the dominant allele in the phenotype, carries the recessive allele.
    • Crossing two heterozygous individuals of the F1 generation (e.g., Yy and Yy) results in an F2 generation with a 3:1 ratio of phenotype: 75% expressing the dominant allele and 25% expressing the recessive allele.

Testcross

  • A testcross is a cross between an individual with an unknown genotype and an individual expressing the recessive allele. By analyzing the phenotypes of the offspring, you can deduce the unknown genotype of the individual.
  • By crossing a black dog with a brown dog (bb genotype), you can reveal if the black dog is BB or Bb.

Probability in genetics

  • Probabilities can be used to predict the genotypic and phenotypic ratios of offspring.
  • Multiplication rule: This rule is used to calculate the probabilities of independent events occurring together.
  • Addition rule: This rule is used to calculate the probabilities of mutually exclusive events occurring.

Chromosomes and Inheritance

Chromosomal theory of inheritance

  • Chromosomal theory of inheritance: suggests that genes reside on specific loci on chromosomes.
  • Chromosomes undergo segregation and independent assortment during meiosis, explaining Mendel's observations.
  • Thomas H. Morgan's experiments with Drosophila melanogaster (fruit flies. provided evidence supporting the chromosomal theory.
  • Drosophila is a good genetic study model due to its short generation time, ability to produce many offspring, and easily identifiable traits.
  • Morgan's studies of a white-eye mutation in fruit flies, which is sex-linked, demonstrated that genes are associated with specific chromosomes.

Sex chromosomes

  • Sex chromosomes (X and Y) determine sex in many organisms, including humans.
  • In humans:
    • Males are heterogametic (XY), producing gametes with either an X or a Y chromosome.
    • Females are homogametic (XX), producing gametes with only an X chromosome.
  • Sex-linked genes reside on the X or Y chromosomes.
  • The inheritance patterns for sex-linked genes are different due to differences in chromosome number and structure between genders.

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