Feralis Ch 1 Flashcards
Ionic Bonds
Transfer of electrons from one atom to another where both atoms have different electronegativities
Non-polar covalent bonds
Equal sharing of electrons between two atoms of identical electronegativity
Polar covalent bonds
Unequal sharing of electrons between two atoms of different electronegativities, results in dipole formation
Hydrogen bonds
Weak bond between molecules with a hydrogen attached to a highly electronegative atom and is attracted to a negative charge on another molecule (F, O or N)
5 Properties of water
Excellent solvent, high heat capacity, ice floats, cohesion/surface tension, adhesion
Excellent solvent - water property
Dipoles of H2O break up charged ionic molecules, making it easy for water to dissolve substances
High heat capacity - water property
Water requires large amount of energy to change the temperature degree. Water also has high heat of vaporization
Ice floats - water property
Water expands when frozen and becomes less dense than liquid water. This is because the H bonds become rigid and form crystal that keeps the molecules separated
Cohesion/surface tension - water property
Water can be attracted to like substances because of its H bonds. There is strong cohesion between H2O molecules, producing a high surface tension
Adhesion - water property
Water can also be attracted to unlike substances. Capillary action is the ability of a liquid to flow without external forces (ex. up a vertical paper)
Organic molecules
Made of carbon atoms. Macromolecules from monomers, monomers form polymers
Hydroxyl
OH functional group, polar, hydrophilic
Carboxyl
COOH functional group, polar, hydrophilic, weak acid
Amino
NH2 functional group, polar, hydrophilic, weak base
Phosphate
PO4(3-) functional group, polar, hydrophilic, acid
Carbonyl
C=O functional group, polar, hydrophilic. Incorporated into aldehyde and ketone
Aldehyde
H-C=O functional group, polar, hydrophilic
Ketone
R-C=O functional group, polar hydrophilic
Methyl
CH3 functional group, non-polar, hydrophobic
Monosaccharide
Single sugar molecule (ex. glucose and fructose)
Disaccharide
Two sugar molecules joined by glycosidic linkage (occurs via dehydration reaction) (ex. sucrose, lactose, maltose)
Polysaccharide
Series of connected monosaccharides; polymer. Bonds form via dehydration synthesis and breakdown via hydrolysis
Sucrose
Disaccharide, glucose + fructose
Lactose
Disaccharide, glucose + galactose
Maltose
Disaccharide, glucose + glucose
Carbohydrates
Includes sugars, starches and fibres. Composed of the “-saccharides”
Starch
A carbohydrate, a polymer of alpha-glucose molecules, stores energy in plant cells
Glycogen
A carbohydrate, a polymer of alpha-glucose molecules, stores energy in animal cells
Cellulose
A carbohydrate, a polymer of beta-glucose, structural molecules for walls of plant cells and wood
Chitin
A carbohydrate, a polymer similar to cellulose, but each beta-glucose group has a nitrogen containing group (n-acetylglucosamine) attached to the ring, it is structural molecule in fungal cells and insect cytoskeletons
Lipids
Hydrophobic, for insulation, energy storage, make up structural components like cholesterol and phospholipids in membranes, participates in endocrine signalling
Triglycerides (Triacylglycerols)
A lipid, 3 fatty acid chains attached to glycerol backbone, can be saturated or unsaturated
Saturated triglycerides
A lipid, no double bonds, has straight chains, bad for health because straight chains stack densely and form fat plaques
Unsaturated triglycerides
A lipid, contains double bonds that cause kinks, better for health because chains can stack less densely, can be cis or trans
Phospholipids
A lipid, composed of 2 fatty acids and a phosphate group (+R) attached to a glycerol backbone. It is amphipathic
Steroids
A lipid, composed of three 6-membered rings and one 5-membered ring, includes (sex) hormones, cholesterol, corticosteroids
Waxes
A lipid, esters of fatty acids and monohydroxylic alcohols, used as protective coating or exoskeletons (lanolin)
Carotenoids
A lipid, fatty acid carbon chains with conjugated double bonds and 6-membered C-rings at each end. Includes pigments that produce colours in plants and animals. Subgroups are carotenes (orange) and xanthophylls (yellow)
Porphyrins (tetrapyrroles)
A lipid, 4 joined pyrrole rings that often complex with a metal (ex. porphyrin heme complexes with Fe in hemoglobin; chlorophyll with magnesium)
Adipocytes
A lipid, specialized fat cells, two categories are white fat cells and brown fat cells
White fat cells
An adipocyte, a lipid, composed primarily of triglycerides with a small layer of cytoplasm around it
Brown fat cells
An adipocyte, a lipid, have considerable cytoplasm, lipid droplets scattered throughout, and lots of mitochondria
Glycolipids
A lipid, similar to phospholipids but have a carbohydrate group instead of phosphate group
Lipoproteins
A lipid, transports the insoluble lipids in the blood, are lipid cores surrounded by phospholipids and apolipoproteins
Cell membrane fluidity
Part of lipids, cell membranes need to maintain certain degree of fluidity and are capable of changing membrane fatty acid composition to do so
Cell membrane fluidity in cold weather
Cell membrane becomes more rigid. To avoid rigidity, cholesterol, monounsaturated and polyunsaturated fatty acids are incorporated into the membrane, which increases fluidity
Cell membrane fluidity in warm weather
Cell membrane becomes more fluid and flexible. To avoid cell membrane collapse, cholesterol is added to restrict movement. Fatty acid tails are saturated so they become straight and pack tightly, which decreases fluidity
Protein
Polymers of amino acids joined by peptide bonds. Have alpha-carbon attached to side chain, H, amino group and carboxyl group. Functions include structure, storage, transport, defence (antibodies) and enzymes. RNA can act as an enzyme sometimes (ex. ribozymes)
Storage proteins
casein in milk, ovalbumin in egg whites, zein in corn seeds
Transport proteins
Hemoglobin carries oxygen, cytochromes carry electrons
Enzymes
Catalyze reactions based on substrate concentration, does not change spontaneity of a reaction. Enzyme efficiency determined by temperature and pH. Amylase catalyzes reactions that breaks the alpha-glycosidic bonds in starch
Cofactors
Non-protein molecule that assists enzymes by donating or accepting some component of a reaction (such as electrons or functional groups), can be organic (called coenzyme, ex. vitamins) or inorganic (ex. metal ions like Fe2+ and Mg2+)
Holoenzyme
Union of cofactor and enzyme
Apoenzyme/Apoprotein
Enzyme is not combined with a cofactor
Coenzyme
Organic cofactor, ex. vitamins, usually donate or accept electrons
Prosthetic group
Cofactor binds tightly or covalently bound to an enzyme
Simple protein
Formed entirely of amino acids
Albumins and globulins
Functional proteins that act as carriers or enzymes
Scleroproteins
Fibrous proteins, have structural function (ex. collagen)
Conjugated proteins
Simple protein + non-protein
Lipoprotein
Protein bound to lipid
Mucoprotein
Protein bound to carbohydrate
Chromoprotein
Protein bound to pigmented molecule
Metalloprotein
Protein complexed around metal ion
Nucleoprotein
Contains histone or protamine, bound to nucleic acid
Primary protein structure
Sequence of amino acids connected by peptide bonds
Secondary protein structure
3D shape resulting from hydrogen bonding between amino and carboxyl groups of adjacent amino acids (alpha helix or beta sheet). Hydrogen bonds, disulfide bonds and Van Der Waals forces
Tertiary protein structure
3D folding pattern resulting from non-covalent interactions between amino acid R groups (side chain interaction). Non-covalent interactions include H bonds, ionic bonds, hydrophobic effect (R groups push away from water), disulfide bonds, and Van Der Waals forces
Quaternary protein structure
3D shape of a protein that is a grouping of 2 or more separate peptide chains
Protein structure
All proteins have primary structure, most have secondary structure, larger proteins may have tertiary and quaternary structure.
3 main protein categories
Globular proteins, fibrous/structural proteins and membrane proteins
Globular proteins
A protein category, somewhat water soluble, mostly dominated by tertiary structure, diverse range of functions including: enzymatic, hormonal, intercellular and intracellular storage and transport, osmotic regulation, immune response
Fibrous/structural proteins
A protein category, not water soluble, mostly dominated by secondary structure, made of long polymers, function to maintain and add strength to cellular and matrix structure (ex. collagen or keratin)
Membrane protein
A protein category, includes proteins that function as membrane pumps, channels or receptors
Protein denaturation
Protein is reversed back to primary structure, usually irreversible. Denaturation may be reversed with removal of denaturing agent. Implies that all information needed for a protein to assume its native state (its folded functional form) is encoded in its primary structure
Protein denaturation vs protein digestion
Denaturation reverses protein to primary structure. Digestion eliminates all protein structure, including the primary structure
Nucleotides
Monomers that make up nucleic acids and consist of a nitrogenous base, a 5-carbon deoxyribose sugar and a phosphate group.
Nucleosides
Sugar and nitrogenous base
Nitrogenous base
Nitrogen-containing compound that makes up a nucleotide and can vary based on DNA or RNA.
Nitrogenous bases of DNA
A and T pair with 2 H bonds. C and G pair with 3 H bonds
Nitrogenous bases of RNA
A and U (uridine) pair with 2 H bonds. C and G pair with 3 H bonds
Pyrimidines
1 ring, cytosine, uracil, thymine
Purines
2 rings, adenine, guanine
DNA
Deoxyribose sugar, 2 antiparallel strands of a double helix
RNA
Ribose sugar, single stranded
Cell theory
i. All living organisms are composed of one or more cells ii. The cell is the basic unit of structure, function, and organization in all organisms iii. All cells come from preexisting, living cells iv. Cells carry hereditary information
RNA world hypothesis
Proposes that self-replicating RNA molecules were precursors to current life. States that RNA stores genetic information (similar to DNA) and catalyzes chemical
reactions (similar to enzyme). RNA may have played a major role in the evolution of cellular life. RNA is unstable, compared to DNA, due to its extra hydroxyl group that makes it more likely to participate in chemical reactions!
Central dogma of genetics
Information must travel from DNA -> RNA -> protein
Ranking Biological Scale
Relative sizes of different cell elements at structures
Stereomicroscope (light)
Uses visible light to view the surface of a sample.
Pro: can view living samples
Con: has low light resolution compared to a compound microscope
Compound Microscope (light)
Uses visible light to view a thin section of a sample.
Pro: can view some living samples (single cell layer)
Con: may require staining for good visibility
Phase Contrast Microscope
Uses light phases and contrast for a detailed observation of living organisms, including internal structures.
Pro: has good resolution and contrast
Con: not ideal for thick samples and produces a “Halo Effect” around perimeter of samples
Confocal Laser Scanning Microscope and Fluorescence
Used to observe thin slices while keeping a sample in tact; common method for viewing chromosomes during mitosis
Pro: can observe specific parts of a cell using fluorescent tagging
Con: can cause artifacts
Note: confocal laser scanning microscopes can be used without fluorescence as well, in which laser light is used to scan a dyed specimen and display the image digitally
Scanning Electron Microscope (SEM)
Pro: view surface of 3D objects with high resolution
Cons: can’t use on living samples, preparation is extensive as sample needs to be dried and coated, is costly
Cryo Scanning Electron Microscope (Cryo SEM)
Pro: sample is not dehydrated so you can observe samples in their more ‘natural form’
Cons: can’t use on living samples, samples must be frozen, which can cause artifacts
Transmission Electron Microscope (TEM)
Pros: can observe very thin cross- sections in high detail, and can observe internal structures with very high resolution
Cons: cannot be used on living samples, preparation of sample is extensive, and technique is costly
Electron Tomography
not a type of microscope, but a technique used to build up a 3D model of sample using TEM data
Pro: can look at objects in 3D and see objects relative to one another
Cons: cannot be used on living samples, preparation of sample is extensive, and technique is costly
Centrifugation
Common technique used to prepare a sample for observation or further experimentation. It spins and separates liquified cell homogenates into layers based on density.
Order of pellet in centrifugation
Cell parts separate with the most dense pelleting first and least dense separating last. We spin and extract the dense pellet, and spin again and repeat. In cells, starting from first component to pellet at the bottom and progressively spinning faster, the order is: nuclei layer -> mitochondria/ chloroplasts/lysosomes → microsomes/small vesicles → ribosomes/viruses/larger macromolecules
Differential centrifugation
Relies on density, shape, and speed at which macromolecule travels
Density centrifugation
Based on density, separates cell parts within the same pellet group created from differential centrifugation. Forms continuous layers of sediment: insoluble proteins can be found in the pellet, soluble proteins remain in the supernatant liquid above the pellet.
Reaction at equilibrium
The rate of formation of reactants and products is equal and there is 0 net production.
Anabolic reactions
Chemical reactions in which small molecules are assembled into larger molecules
Catabolic reactions
Chemical reactions in which large molecules are broken down into small molecules
Catalysts
Enzymes, lowers activation energy of a reaction, accelerates the rate of the overall reaction, enzymes are substrate specific, enzymes remain unchanged during reaction, catalyzes both forward and reverse directions of the reaction, varying function based on pH and temperature, has an active site that binds substrates via induced fit
ATP
Common source of activation energy, stores its potential energy in the form of chemical energy, formed via phosphorylation, ADP and Pi come together using energy from an energy rich molecule like glucose.
Allosteric enzymes
Enzyme that has both an active site for substrate binding and an allosteric site for the binding of an allosteric effector (can be an activator or inhibitor)
Competitive inhibition
A substance that mimics the substrate and inhibits the enzyme by binding at the active site. The effect of competitive inhibition can be overcome by increasing substrate concentration
Uncompetitive / anti-competitive inhibition
Occurs when an enzyme inhibitor binds only to the formed enzyme-substrate (ES) complex (and not to the free enzyme), preventing formation of product. Vmax and Km are lowered
Vmax
Maximum velocity of the enzyme
Km, Michaelis constant
Represents the substrate concentration at which the rate of reaction is half of Vmax.
Relationship between Km and binding affinity
Inverse relationship; higher Km equals worse
substrate binding, lower Km equals better substrate binding.
i. A small Km indicates that an enzyme only requires a small amount of substrate to become saturated. Hence, Vmax is reached at relatively low substrate concentrations.
ii. A large Km indicates the need for high substrate concentrations to achieve Vmax.
Cooperativity
Phenomenon that occurs where an enzyme becomes more receptive to additional substrate molecules after one substrate molecule binds to the active site
i. Example: hemoglobin is a quaternary protein with 4 subunits that each has an active site for binding oxygen. As the first oxygen binds, the other active sites become increasingly likely to bind oxygen.
ii. Note: hemoglobin is not an enzyme, but is used here as a simple example of biological cooperativity that you will encounter later.
8 types of membrane proteins
Channel proteins, recognition proteins, ion channels, porins, carrier proteins, transport proteins, adhesion proteins, receptor proteins
Channel proteins
A type of membrane protein, provide a passageway through the membrane for hydrophilic (water-soluble), polar, and charged substances
Recognition proteins
A type of membrane protein, type of glycoprotein (have an attached oligosaccharide) that is used to distinguish between self and foreign (e.g major-histocompatibility complex on macrophage)
Ion channels
A type of membrane protein, used to pass ions across the membrane and referred to as gated channels in nerve and muscle cells
i. Can be voltage-gated (respond to
difference in membrane protein), ligand-gated (chemical binds to open channel), or mechanically-gated (respond to pressure, vibration, pressure)
Porins
A type of membrane protein, allows the passage of certain ions and small polar molecules; increase the rate of water passing in kidney and plant root cells; tend to be less specific - if you can fit through the large passage, you can go through
Carrier proteins
A type of membrane protein, specific to movement across the membrane via integral membrane protein; changes shape after binding to specific molecule that enables it to be passed across (e.g glucose into the cell)
Transport proteins
A type of membrane protein, includes active transport that uses ATP (e.g sodium-potassium pump) and facilitated diffusion that does not use ATP
Adhesion proteins
A type of membrane protein, attach cells to neighboring cells and provide anchors for stability via internal filaments and tubules
Receptor proteins
A type of membrane protein, serve as binding sites for hormones and other trigger molecules
3 membrane properties
Phospholipid membrane permeability, cholesterol, glycocalyx
Phospholipid membrane permeability
A type of membrane property, allows small, uncharged, non-polar, hydrophobic molecules to freely pass the membrane. Polar molecules may cross if they are small and uncharged. Every other type of substance requires a transporter
Cholesterol
A type of membrane property, adds rigidity to animal cell membranes under normal conditions and maintains fluidity of the membrane at lower temperatures; sterols provide analogous function in plant cells
Note: prokaryotes do not have cholesterol in their membranes - use hopanoids instead
Glycocalyx
A type of membrane property, a carbohydrate coat that covers the outer face of the cell wall of some bacteria and the outer face of the plasma membrane in some animal cells; consists of glycolipids attached to the plasma membrane, and glycoproteins that may serve as recognition proteins. Functions include adhesive capabilities, barrier to infection, or markers for cell-cell recognition
Peripheral membrane proteins
Generally hydrophilic and are held in place by H- bonding and electrostatic interactions. Can disrupt/ detach them by changing salt concentration or pH
Integral proteins
Hydrophobic, can be destroyed using detergent
Chromatin
General packaging structure of DNA around proteins in eukaryotes; tightness in packaging depends on cell stage
Chromosomes
Tightly condensed chromatin when the cell is ready to divide
Histones
DNA coils around it into bundles called nucleosomes; these bundles are wrapped around 8 histone proteins
Nucleosomes
DNA coiled around 8 histone proteins
Nucleolus
Inside of the nucleus and serves as the site of ribosome synthesis
Ribosome synthesis
Synthesized using rRNA and ribosomal proteins, which are imported from the cytoplasm. Once ribosomal subunits form, they are exported to the cytoplasm for final assembly into a complete ribosome.
Nucleus
Bound by proteins like RNA polymerase and histones. There is no cytoplasm in the nucleus, there is nucleoplasm. Found only in eukaryotic cells, not in prokaryotic cells
Nuclear Lamina
Dense fibrillar network inside of the nucleus of eukaryotic cells that provides mechanical support; helps regulate DNA replication, cell division, and chromatin organization
Nucleoid
Irregular shaped region within prokaryote cells that contains all or most of the cell’s genetic material. Found only in prokaryotic cells
Cytoplasm
This is an area, not a structure. All of the cell’s metabolic activity and transport occur here, and the area includes the cytosol and organelles
Cytosol / Cytoplasmic Matrix
Unlike the cytoplasm, it doesn’t include the components suspended within the gel-like substance, it is JUST the gel-like substance.
Ribosomes
Organelles made of rRNA, function to make proteins
i. Composed of two subunits, 60S + 40S
= 80S in eukaryotes and 50S+ 30S = 70S in prokaryotes; the two subunits are produced inside of the nucleolus and moved into the cytoplasm where they are assembled into a single 80S ribosome
ii. A larger S value (Svedberg unit) indicates a heavier molecule
Rough ER
ER studded with ribosomes and creates glycoproteins by attaching polysaccharides to polypeptides as they are assembled by ribosomes; in eukaryotes, the rough ER is continuous with the outer nuclear membrane
Smooth ER
ER without ribosomes that synthesizes lipids and steroid hormones for export. In liver cells, the smooth ER function to break down toxins, drugs, and toxic by- products from cellular reactions. Smooth and striated muscle have smooth ER’s called sarcoplasmic reticulum that store and release ions like Ca2+
Lysosomes
Vesicles produced from the Golgi that contain digestive enzymes with low pH, and functions in apoptosis, and to break down nutrients, bacteria, and cell debris. Any enzyme that escapes from lysosomes remains inactive in the neutral pH of cytolysis
Golgi
Transport of various substances in vesicles and has flattened sacs known as cisternae. The cis face is for incoming vesicles, while the trans face is for secretory vesicles
Peroxisomes
Organelles common in the liver and kidney that function to breakdown substances (H2O2 + RH2 → R + 2H2O), fatty acids, and amino acids
i. In plant cells, peroxisomes modify by-products of photorespiration. In germinating seeds, peroxisomes are called glyoxysomes that break down stored fatty acids to help generate energy for growth
ii. Peroxisomes produce H2O2, which they use to oxidize substrates and can also break down H2O2 if necessary (H2O2 → H2O + O2)
Microtubules
Made up of the protein tubulin and serves to provide support and motility for cellular activities; is a spindle apparatus which guides chromosomes during division; Can be found in flagella and cilia of all animal cells and lower plants like mosses and ferns in a 9+2 array (9 pairs of microtubules with 2 singlets in the center)
Intermediate Filaments
Provides support for maintaining cell shape (ex: keratin)
Microfilament
Made of actin and involved in cell motility; found in skeletal muscle, amoeba pseudopod, and cleavage furrows
Microtubule Organizing Centers (MTOCs)
Structures that include centrioles and basal bodies and are found at the base of each flagellum and cilium. Found in a 9x3 array. Plant cells lack centrioles and divide via cell plates rather than cleavage furrows, but plants still do have MTOCs
Transport Vacuoles
Moves materials between organelles or between organelles and the plasma membranes
Food Vacuoles
Temporary receptacles of nutrients that merge with the cytoplasm in order to breakdown food
Central Vacuoles
Large, occupy most of the plant cell interior, exert turgor when fully filled to maintain rigidity, store nutrients, carry out functions performed by lysosomes in animal cells, and have a specialized membrane called a tonoplast
Storage Vacuoles
Location where plants store starch, pigments, and toxic substances such as nicotine
Contractile Vacuoles
Found in single-celled Protista organisms like amoeba and paramecium; function to collect and pump excess water out of the cell via active transport to prevent bursting
Cell Walls
Functions to provide support in plants, fungi, protists, and bacteria; sometimes in presence with a secondary cell wall that develops beneath the primary cell wall
Cellulose
Makes up plant cell walls
Chitin
Makes fungi cell walls
Peptidoglycan
Makes bacteria cell walls
Polysaccharides
Makes archaea cell walls
Extracellular Matrix
Found in animals in area between adjacent cells; occupied by fibrous structural proteins, adhesion proteins, and polysaccharides secreted by cells
Extracellular matrix functions
Provides mechanical support and helps bind adjacent cells. Collagen is the most common protein that binds adjacent cells, but, there is also integral and fibronectin, which is a network of collagen and proteoglycans connected to interns in the cell membrane via fibronectin or laminin. The ECM also functions in transmitting mechanical and chemical signals between the inside and outside of the cell
2 methods for the cell to adhere to ECM
Focal adhesions and hemidesmosomes
Focal adhesions
Method for the cell to adhere to ECM, involve connection of the ECM to actin filaments in the cells
Hemidesmosomes
Method for the cell to adhere to ECM, connection of ECM to intermediate filaments like keratin
Fibroblasts
Cells that produce collagen and other connective tissue elements
Plastids
Organelles found in plant cells, includes chloroplasts leucoplasts and chromoplasts
Leucoplasts
A plastid. Specializes to store starch, lipids, proteins, as amyloplasts, elaioplasts, and proteinoplasts, respectively
Chromoplasts
A plastid. Stores carotenoids
Mitochondria
Double-layered organelles that make ATP, and serve as the site of fatty acid catabolism, or Beta-oxidation; have their own circular DNA and ribosomes
Cytoskeleton
Includes microtubules (ex. flagella and cilia), microfilaments, intermediate filaments; found in eukaryotic cells, aids in cell division, cell crawling, and the movement of cytoplasm and organelles
Hypotonic solution, plant context
Normal state of plant cells; vacuole swells and becomes turgid. Fungal cells also remain turgid due to the cell wall
Isotonic solution, plant context
Plant cell is flaccid
Hypertonic solution, plant context
Cell is plasmolyzed — the cytoplasm is pulled away from the cell wall
Cytolysis
Cell bursts due to an osmotic imbalance that has caused excess water to diffuse into the cell, occurs in animal cells
Endomembrane System
Network of organelles and structures, either directly or indirectly connected, that function in the transport of proteins and other macromolecules into or out of the cell. Includes the plasma membrane,
endoplasmic reticulum, Golgi apparatus, nuclear envelope, lysosomes, vacuoles, vesicles, and endosomes, but not the mitochondria
Cell movement
Occurs via flagella, which undulate like snakes, and via cilia, which beat in a rapid back and forth motion
2 methods of circulation
Intracellular Circulation and extracellular circulation
Intracellular Circulation
i. Brownian movement: random
particle movement due to kinetic energy, spreads small suspended particles throughout cytoplasm
ii. Cyclosis/streaming: circular motion of cytoplasm around cell transport molecules
iii. Endoplasmic reticulum: provides channel through cytoplasm, provides direct continuous passageway from plasma membrane to nuclear membrane
Extracellular Circulation
i. Diffusion: if cells in close contact with external environment, can suffice for food and respiration needs. Also used for transport of materials between cells and interstitial fluid around cells in more complex animals
ii. Circulatory system: required by complex animals with cells too far from the external environment
Junctions and types of junctions
Structures that consist of protein complexes that connect neighbouring cells: anchoring junctions, tight junctions, gap junctions, plasmodesmata
Anchoring Junctions
Includes desmosomes, which are keratin filaments attached to adhesion plaques which bind adjacent cells together via connecting adhesion proteins, providing mechanical stability by holding cellular structures together. Present in animals cells in tissues with mechanical stress including cells in the skin epithelium and cervix/uterus
Tight Junctions
Junction that completely encircles each cell, producing a seal that prevents the passage of materials between cells, characteristic of cells lining the digestive tract. Materials must actually enter the cells (by diffusion or active transport) in order to pass through the tissue in animal cells
Gap Junctions
Narrow tunnels between animal cells (connexins) that prevent cytoplasms of each cell from mixing, but allow passage of ions and small molecules; essentially channel proteins of two adjacent cells that are closely aligned. Tissues like the heart include them to quickly pass electrical impulses
Plasmodesmata
A type of junction. Narrow tunnels between plant cells (narrow tube of endoplasmic reticulum - desmotubule - that exchanges material through cytoplasm surrounding the desmotubule)
Eukaryotes
Include all organisms except for bacteria, cyanobacteria, and archaebacteria
Prokaryotes
Have a plasma membrane, circular DNA, ribosomes, cytoplasm, and cell wall. In prokaryotes, there is no nucleus, single circular naked double-stranded DNA (no chromatin), Ribosomes (50S + 30S = 70S), Cell walls (peptidoglycan), flagella
Hypertonic
higher solute concentration
Hypotonic
lower solute concentration
Isotonic
equal solute concentration
Bulk Flow
Collective movement of substances such as blood in the same direction in response to a force or pressure
Passive Transport
Includes simple diffusion, osmosis, dialysis (diffusion of different solutes across a selectively permeable membrane), plasmolysis (movement of water out of a cell that results in its collapse), facilitated diffusion, countercurrent exchange (diffusion by bulk flow in opposite directions such as blood and water in fish gills)
Active Transport
Movement of molecules against their concentration gradients requiring energy. Usually solutes like small ions, amino acids, monosaccharides
Primary active transport
Energy (ATP) is directly used to move against concentration gradients
Secondary active transport
Energy is indirectly used to move against concentration gradient (usually with an ion moving down its concentration gradient) - can be anti-port or co-transport
Group translocation
Seen in prokaryotes when the substance being transported across the membrane is chemically altered in the process, which prevents it from diffusing back out
3 types of endocytosis
These are 3 types of active transport: Phagocytosis, Pinocytosis, Receptor-mediated Endocytosis
Phagocytosis
A type of endocytosis, undissolved material
(solid) enters cell; white blood cell engulfs the material as the plasma membrane wraps around the substance
Pinocytosis
A type of endocytosis, plasma membrane invaginate around dissolved material (liquid)
Receptor-mediated Endocytosis
A type of endocytosis, form of pinocytosis in which specific molecules called ligands bind to receptors. Proteins that transport cholesterol in blood (LDL) and hormones that target specific cells use this technique
Gibbs Free Energy
Tells us whether a given chemical reaction can occur spontaneously: G = H - TS (H is enthalpy, T is temperature, and S is entropy). If △G is negative, the reaction can occur spontaneously. If △G is positive, the reaction is non-spontaneous.
Gibbs Free Energy change
Chemical reactions can be “coupled” together if they share intermediates. The sum of the △G values for each reaction. An unfavorable reaction with a positive △G1 value can be driven by a second, highly favorable reaction (negative △G2 value where the
magnitude of △G2 > magnitude of △G1
Spontaneous change
Gibbs free energy goes down, stability goes up, and work capacity goes down
Exergonic (spontaneous) reactions
Free energy is released and △G is less than 0
Endergonic (non-spontaneous) reactions
Free energy is required and △G is greater than 0
Cellular Respiration
Overall oxidative, exergonic process (△G = -686 kcal/mol) that breaks down glucose to derive ATP energy. High energy H atoms are removed from organic molecules (dehydrogenation), aerobic process. Four major steps: glycolysis, pyruvate decarboxylation, the Krebs Cycle, and the electron transport chain. Equation: C6H12O6 + 6O2 –> 6CO2 + 6H2O + ATP
External respiration
Entry of air into the lungs and subsequent gas exchange between alveoli and blood
Internal respiration
Exchange of gas between blood and the cells.
Glycolysis goal and location
Decomposition of glucose into pyruvate in the cytosol
Glycolysis start and end products
Start with 1 glucose. 2 ATP added in the intermediate reactions. 2 NADH, 4 ATP, and 2 pyruvate formed (Net 2 ATP formed)
Glycolysis ATP production
ATP produced via substrate level phosphorylation, which involves direct enzymatic transfer of a phosphate to ADP (no extraneous carriers needed)
Hexokinase in glycolysis
Phosphorylates glucose, which is important as this step is irreversible and glucose can’t diffuse out of the cell
Phosphofructokinase (PFK) in glycolysis
Adds second phosphate, forming fructose 1,6- bisphosphate, which is irreversible and commits the glucose to glycolysis. Major regulatory point of glycolysis and is a point of allosteric regulation that controls the overall rate of glycolysis (rate limiting step)
Pyruvate Decarboxylation location, start and end products, enzyme
Mitochondrial matrix. Pyruvate and co-enzyme A combine and produce 1 NADH, 1 CO2 and 1 Acetyl CoA (Net: 2 NADH, 2 CO2 and 2 Acetyl CoA since 2 pyruvate formed in glycolysis). Reaction is catalyzed by PDC enzyme (pyruvate dehydrogenase complex)
Krebs Cycle/Citric Acid Cycle/Tricarboxylic Acid Cycle location and start and end products
Occurs in the mitochondrial matrix. Acetyl CoA merges with oxaloacetate to form citrate, and
the cycle continues with 7 intermediates. 3 NADH, 1 FADH2, 1 ATP (via substrate level phosphorylation) and 2 CO2 are produced per turn. Net of 6 NADH, 2 FADH2, 2 ATP (technically GTP), 4 CO2 as the cycle occurs for each of the two pyruvate formed from one glucose molecule. The CO2 produced here is the CO2 animals exhale during breathing
Electron Transport Chain (ETC) location
Inner membrane / cristae (the folds which increase surface area for more ETC action)
Electron Transport Chain (ETC) goal
Oxidative phosphorylation occurs here, which is the process of ADP → ATP from NADH and FADH2 via passing of electrons through various carrier proteins; energy doesn’t accompany the phosphate group but comes from the electrons in the ETC establishing an H+ gradient that supplies energy to ATP synthase
Electron Transport Chain (ETC): NADH vs FADH2
NADH makes more energy than FADH2, and more H+ is pumped across per NADH (both of which are coenzymes) (3:2 yield)
Electron Transport Chain (ETC): final electron acceptor and final product
Final electron acceptor: Oxygen, which combines with native H+ to form water
Final product: Water and ATP
Electron Transport Chain (ETC): ATP synthase
Makes ATP by using the pH and electrical gradient established by electron carriers that ‘extract energy from NADH and FADH2 while pumping protons into the intermembrane space’. It makes ATP as it shuttles H+ back into the inner matrix
Electron Transport Chain (ETC): Coenzyme Q (CoQ) / Ubiquinone
Soluble carrier dissolved in the membrane that can be fully reduced/ oxidized as it passes electrons
Electron Transport Chain (ETC): Cytochrome C
Protein carrier, common in many living organisms, used for genetic relations, have nonprotein parts like iron that donate or accept electrons for redox reactions
ETC coupled mechanism
Couples flow of electrons with endergonic pumping of H+ across the cristae membrane
Total energy from 1 glucose in eukaryotes vs prokaryotes
~36 ATP in eukaryotes and ~38 ATP in prokaryotes (not actual yield as mitochondrial efficacy varies)
Reasoning for difference between ATP totals in eukaryotes and prokaryotes
Prokaryotes have no mitochondria so they, unlike eukaryotes, don’t need to transfer the two NADH molecules into the mitochondrial matrix - which is done via active transport thus costing 1 ATP each. Side note - pyruvate is also actively transported into the mitochondrial matrix (in eukaryotes) but its transport is secondary active (symport with protons) and doesn’t directly use ATP.
Mitochondria
The outer membrane, intermembrane
space (H+ build up), inner membrane (ETC), and mitochondrial matrix (Krebs) are involved in cell respiration
Chemiosmosis
Mechanism of ATP generation that occurs when energy is stored in the form of a proton concentration gradient across a membrane. Krebs Cycle produces NADH/FADH2 which are oxidized and cause H+ to be
transported from the mitochondrial matrix to the intermembrane space. A pH and electrical charge gradient is created and ATP uses the kinetic energy from the flow established by this gradient (proton motive force) to create ATP as protons flow through the channel.
ATP (adenosine triphosphate)
An RNA nucleotide (due to its ribose sugar)
i. Is an unstable molecule because the 3 phosphates in ATP are negatively charged and repel one another
ii. When one phosphate group is
removed via hydrolysis, a more stable ADP molecule results
iii. The change from a less stable molecule to a more stable molecule always releases energy
iv. Provides energy for all cells by transferring phosphate from ATP to another molecule
Anaerobic Respiration (cytosol)
Includes glycolysis and fermentation
Reasoning for why fermentation occurs
Aerobic respiration regenerates NAD+ via O2, which is required for continuation of glycolysis. Without O2, there would be no replenishing of NAD+, so NADH accumulates and no new ATP can be made, so fermentation occurs
Alcohol Fermentation: location
Occurs in plants, fungi (e.g yeasts), and bacteria (e.g botulinum)
Alcohol Fermentation: start and end products
Pyruvate → acetaldehyde + CO2, then acetaldehyde → ethanol (and NADH → NAD+)
Alcohol Fermentation: final electron acceptor and final product
Acetaldehyde is the final electron acceptor, thus forming the final product of ethanol.
Lactic Acid Fermentation: location
Occurs in human muscle cells and other microorganisms
Lactic Acid Fermentation: start and end products
Pyruvate → lactate (and NADH → NAD+)
Lactate is transported to liver for conversion back to glucose once surplus ATP available
Facultative Anaerobes
Use oxygen when it’s present (more efficient) but switch to fermentation/anaerobic respiration if oxygen is not present
Obligate anaerobes
Cannot live in presence of oxygen
Similarity between fermentation and cellular respiration
Both use glycolysis and produce a pyruvate molecule.
Alternative Energy Sources
When glucose supply is low, the body uses other energy sources, in the priority order of other carbohydrates (4 calories/gram), fats (10 calories/gram, Stores more energy than carbohydrates and proteins per carbon. Carbons in fat are in a more reduced state), and proteins (4 calories/gram).
Alternative Energy Sources: Other carbohydrates
Carbohydrates are converted to glucose or glucose intermediates, and are then degraded in glycolysis or the Krebs cycle.
Alternative Energy Sources: Other carbohydrates - Gluconeogenesis
Produce glucose in liver or kidney
Alternative Energy Sources: Other carbohydrates - Insulin
After large meals, stores glucose as glycogen, activates PFK enzyme. All cells are capable of storing glycogen, but only muscle cells and liver cells store large amounts of glycogen
Alternative Energy Sources: Other carbohydrates -Glucagon
Turns on glycogen degradation to get glucose, inhibits PFK enzyme
Alternative Energy Sources: Other carbohydrates - Disaccharides
Hydrolyzed into monosaccharides, most of which can be converted to glucose or glycolytic intermediates
Alternative Energy Sources: Fats
Triglycerides, in the lumen of the small intestine, are broken down via lipase into monoacylglycerides + fatty acids, which are then absorbed into the enterocytes (cell lining of the small intestine). There, they are reassembled into triglycerides, and then, along with cholesterol, proteins, or phospholipids, are packaged into chylomicrons which move on to the lymph capillary for transport to the rest of the body where they are stored as adipose tissue
Alternative Energy Sources: Fats - Lipases in adipose tissue
Hormone sensitive (e.g to glucagon)
Alternative Energy Sources: Fats - Glycerol
Glycerol → PGAL, enters glycolysis
Alternative Energy Sources: Fats - fatty acid
When fatty acid → Acetyl CoA, every 2
carbon from fatty acid chain makes an Acetyl CoA. Fatty acids in blood combine with albumin, which carries them throughout the bloodstream
Alternative Energy Sources: Fats - Beta oxidation
Fatty acids are broken down for energy, taking place in mitochondrial matrix
i. 2 ATP are spent activating the entire fatty acid chain
ii. Saturated fatty acids produce 1 NADH and 1 FADH2 for every cut into 2 carbons — not the same as for every 2 carbons, as an 18C chain contains 9 2-carbon pieces, but it is only cut 8 times, with each cut being a beta oxidation step
iii. Unsaturated fatty acids produce 1 less FADH2 for each double bond
iv. Results in a BIG yield of ATP, as it yields more ATP per carbon than carbohydrates, with more energy in fats than sugars
v. End product is acetyl-CoA
Alternative Energy Sources: Fats - lipoproteins
Between meals, most lipids of plasma are in the form of lipoproteins (chylomicrons are large lipoproteins). In addition to chylomicrons, there are low and high density lipoproteins. LDLs have low protein density but high fat density, and are unhealthy. HDLs have high protein density and low fat density, and are healthy.
Alternative Energy Sources: Protein
Most amino acids are deaminated in liver, then converted to pyruvate or acetyl CoA or other Krebs cycle intermediates, and enter cellular respiration at these various points, which varies by amino acid.
Alternative Energy Sources: Protein - oxidative deamination
Removes ammonia molecule directly from amino acids. Ammonia is toxic to vertebrates, but most aquatic specific and invertebrates excrete it directly
Alternative Energy Sources: Protein - Converting ammonia
Insects, birds, and reptiles convert ammonia to uric acid. While mammals, sharks, and most amphibians convert ammonia to urea for excretion
Photosynthesis
Harness light energy in order to synthesize glucose: 6CO2 + 6H2O -> C6H12O6 + 6O2. Occurs in chloroplast
Photosynthesis - light-absorbing pigments in plant cells
Chlorophyll a, chlorophyll b, and carotenoids (red, orange, and yellow) function to absorb energy from light. Light is incorporated into electrons, which causes electrons to be excited and become un-stable. These electrons re-emit the absorbed energy, which is then reabsorbed by electrons in nearby pigment molecules.
Photosynthesis - Chlorophyll a structure
Porphyrin ring that consists of alternating double and single bonds. The double bonds are critical for light reactions. The porphyrin ring is also complexed with a Mg atom inside.
Photosynthesis - two special chlorophyll a molecules
P680 and P700
Photosynthesis - P680
Forms pigment cluster 2, PSII
Photosynthesis - P700
Forms pigment cluster 1, PSI
Photosynthesis - Antenna pigments
Chlorophyll b, carotenoids, phycobilins [red algae pigment], xanthophylls capture wavelengths that chlorophyll a does not, and pass energy to chlorophyll a where the direct light reactions occur.
Chloroplast - thylakoid lumen
Location where H+ accumulates as a result of the ETC.
Chloroplast - thylakoids
Suspended within the stroma and their membranes contain the two photosystems, cytochromes, and electron carriers
Chloroplast - stroma
Fluid material that fills area inside the inner membrane and is the location of the Calvin cycle.
Chloroplast - inner and outer membranes of the chloroplast
Consist of a phospholipid bilayer
Chloroplast - thylakoid membrane
Absorbs light
Non-cyclic photophosphorylation location
Thylakoid membrane
Cyclic phosphorylation location
Stroma lamellae — the pieces connecting the thylakoids
Photolysis location
Inside the thylakoid lumen, and passes electrons to the thylakoid membrane for non-cyclic photophosphorylation
Calvin cycle location
Stroma
Chemiosmosis location
Across the thylakoid membrane
Photosynthesis steps
Non-cyclic photophosphorylation, Cyclic Photophosphorylation, Calvin Cycle
Non-cyclic photophosphorylation equation and all steps
Light dependent reaction: H2O + ADP + Pi + NADP + light → ATP + NADPH + O2 + H+.
i. Electrons trapped by P680 in PSII are energized by light
ii. Two excited electrons are passed to a primary electron acceptor (first in the chain of acceptors) from PSII
iii. Excited electrons enter the electron transport chain which consists of PSII that contains cytochrome proteins and Fe2+ as a cofactor; is analogous to oxidative phosphorylation
iv. Two electrons move down the electron transport chain and lose energy, which is used to phosphorylate about 1.5 ATP
vi. Electron transport chain terminates with PSI/P700 where electrons are re- energized by sunlight and passed to another primary electron acceptor. From this point on, the electrons can enter the non-cyclic or cyclic path
vii. If continuing on the non-cyclic path, two electrons pass down a short electron transport chain with proteins like ferrodoxin to combine NADP+ & H+ & 2 electrons to form NADPH
viii. The two electrons lost in step 2 from PSII are replaced when water splits to form 2 electrons, 2 H+, and 1 oxygen molecule. The H+ is used for NADPH formation and the oxygen molecule is released as gas.
Photosystems
There are a few hundred photosystems in each thylakoid and each has a reaction center containing chlorophyll and antenna pigments that funnel energy to it
Cyclic Photophosphorylation
Alternate path that replenishes ATP when the Calvin cycle (next step) consumes it
i. 2 excited electrons from PSI join with protein carriers in the first electron transport chain and generate 1 ATP as they pass through this chain
ii. These 2 electrons are recycled into PSI and continue to have an option to enter the cyclic or non-cyclic path
Calvin Cycle
Dark reaction that fixes 6 CO2 molecules through a cycle that repeats 6 times to ultimately synthesize glucose. Light-independent process, but requires ATP and NADPH produced from light-dependent reactions. Cannot occur without light because it is dependent on the high energy molecules (ATP and NADPH) produced from the light reaction. 6CO2 + 18ATP + 12NADPH + H+ → 18ADP + 18 Pi + NADP+ + 1 glucose (or 2 G3P). Carboxylation, Reduction, Regeneration, Carbohydrate synthesis
Calvin Cycle: Carboxylation
6 CO + 6 RuBP join to form 12 PGA, and is catalyzed by the enzyme RuBisCo, or RuBP carboxylase
Calvin Cycle: Reduction
12 ATP + 12 NADPH convert 12 PGA → 12 G3P or 12 PGAL; energy is incorporated; the by-products NADP+ and ADP go into non-cyclic photophosphorylation
Calvin Cycle: Regeneration
6 ATP convert 10 G3P → 6 RuBP, which allows the Calvin cycle to repeat
Calvin Cycle: Carbohydrate synthesis
Two remaining G3P are used to build glucose.
Plant mitochondria vs Plant chloroplast
Plants do have mitochondria that make ATP, but the ATP from photosynthesis comes from the chloroplast and is used to drive photosynthesis further via the Calvin cycle. Photosynthesis primarily makes glucose for the plant’s own mitochondria to use as energy! We still need mitochondria for plant tissues but the organelle doesn’t make the ATP for photosynthesis, and photosynthesis ATP isn’t used for general cell function!
Chemiosmosis in Chloroplasts
Uses H+ gradient to generate ATP
- H+ ions accumulate inside thylakoids: H+ are released into lumen when water is split by PSII. H+ is also carried into the lumen from stroma by cytochrome between PSII and PSI
- A pH and electrical gradient is created with an approximate pH of 5
- ATP synthase generates ATP: ADP is phosphorylated with Pi to form ATP, and 3 H+ are required to make 1 ATP
- Calvin cycle produces 2 G3P using NADPH, CO2, and ATP: at the end of the electron transport chain following PSI, the 2 electrons produce NADPH
Alternatives to C3 Photosynthesis
Depending on climate, photosynthesis can occur as either photorespiration, C4 photosynthesis, or CAM photosynthesis.
Photorespiration
An alternative to C3 Photosynthesis. Process that involves the fixation of oxygen, instead of CO2, by rubisco but produces no ATP or glucose. Rubisco is not efficient or fast because it will fix both CO2 and oxygen at the same time if both are present. Peroxisomes break down the products of this process.
C4 Photosynthesis steps
An alternative to C3 Photosynthesis. Process that evolved from normal photosynthesis (C3 photosynthesis) and is a type of spatial separation.
i. When CO2 enters the leaf, it is absorbed by mesophyll cells and moved to bundle sheath cells
ii. Instead of being fixed by rubisco into PGA, CO2 combines with phosphoenol pyruvate (PEP) to form oxaloacetate (OAA) by PEP carboxylase in the mesophyll
a. OAA has 4C, therefore it follows C4 photosynthesis
b. OAA is converted to malate, and transferred through plasmodesmata into the bundle sheath cell, which requires conversion of 1 ATP to 1 AMP
c. Malate is converted into pyruvate and CO2. The CO2 can be used in the Calvin cycle and pyruvate is shuttled back into the mesophyll and converted back into PEP.
C4 Photosynthesis purposes
- Move CO2 from mesophyll to bundle sheath cells.
2. Minimize photorespiration and water loss found from the stomata, or lead pores
C4 Photosynthesis - Kranz anatomy
A specialized structure in C4 plants that has mesophyll cells clustered around bundle-sheath cells
C4 Photosynthesis - Hatch-Slack pathway
Explains that little presence of oxygen reduces competition while rubisco is deciding to fix either carbon dioxide or oxygen.
C4 Photosynthesis - climate
C4 photosynthesis is found in hot, dry climates as it allows for a faster fixation speed and is more efficient. Typically occurs in plants like corn and
sugarcane
C4 Photosynthesis - drawback
The use of extra ATP to pump 4C compounds to bundle sheath cells
CAM Photosynthesis steps
An alternative to C3 Photosynthesis. Crassulacean acid metabolism
i. PEP carboxylase fixes CO2 + PEP to OAA, forming malic acid
ii. Malic acid is shuttled into the vacuole of the cell
iii. At night, when stomata are open (opposite of normal), PEP carboxylase is active, causing malic acid to accumulate in the vacuole
iv. During the day, stomata are closed. Malic acid is out of the vacuole and converted back into OAA, which requires 1 ATP, and releases CO2 that moves onto the Calvin cycle with rubisco, and PEP
CAM Photosynthesis advantage
Photosynthesis can proceed during the day while stomata are closed, thereby reducing water loss. Therefore, this process is beneficial in cacti and crassulacean plants.
As leaves age
Chlorophyll breaks down to extract valuable components like Mg2+, and carotenoids become visible
Splitting of water in the light reactions
Provides two electrons for non-cyclic photophosphorylation, and are incorporated into NADPH and the Calvin cycle
Cell division
Nuclear division (karyokinesis), followed by cytokinesis
In diploid cells
2 copies of every chromosome, which forms a pair of homologous chromosomes. Humans have 46 chromosomes, or 23 homologous pairs. One chromosome is made up of 2 sister chromatids. Humans have a total of 92 chromatids
Mitosis
Cell division in somatic cells. Microtubule organizing centers (MTOCs), or centrosomes, are key players in cell division. A pair of MTOCs lay outside the nucleus in animal cells, and each MTOC contains a pair of centrioles. Plants have MTOCs called centrosomes, but they are not composed of centrioles. Prophase, metaphase, anaphase, telophase, cytokinesis
Prophase
Nucleus disassembles, nucleolus disappears, chromatin condenses into chromosomes, and nuclear envelope breaks down. The mitotic spindle forms, and microtubules (composed of tubulin) begin connecting to kinetochores.
Metaphase
Chromosomes line up single file along the center of the cell, forming a chromatid complete with a centromere and kinetochore. Karyotyping is performed when cells are in metaphase.
Anaphase
Microtubules shorten and each chromosome is pulled apart into 2 chromatids. Once separated, the chromatid becomes a chromosome, and the chromosome number doubles. The microtubules pull the chromosomes to opposite poles of the cell, a process known as disjunction. At the end of this phase, each pole has a complete set of chromosomes, same as the original cell before replication. This is the shortest step of mitosis. 92 chromosomes in human because the sister chromatids are split, but the cell is not split yet.
Telophase
Nuclear envelope develops. The chromosomes unravel into chromatin and the nucleoli reappears
Cytokinesis
Begins during the later stages of mitosis, usually begins towards the end of anaphase. Involves the division of cytoplasm to form two cells
Cytokinesis in animal cells
Cleavage furrow forms, which involves the shortening of actin and myosin microfilaments and the plasma membrane is pulled into the center of the cell
Cytokinesis in plant cells
Cell plate forms, which involves vesicles from Golgi bodies migrating and fusing to form a cell plate. As the plate grows, it merges with the plasma membrane, eventually separating the two new cells. Formation of the cell plate doesn’t actually separate cells from each other; the middle lamella (cell plate) cements adjacent cells together
G1
Cell increases in size and lots of proteins and ribosomes are made. The G1 checkpoint ensures that everything is ready for DNA synthesis, and the phase as a whole is the most variable in length of all phases depending on cell type
S
DNA synthesis occurs where a new DNA molecule is replicated from the first, creating sister chromatids
G2
Rapid cell growth occurs, organelles are replicated, and genetic material prepares for cell growth
Interphase vs Mitosis
More time is spent in interphase (G1, S, G2) than in mitosis. Interphase comprises about 90% of the cell cycle.
Interphase
Growth occurs in all 3 interphase phases (G1, S, G2), not just the G phases.
Checkpoints
Occurs throughout the cell cycle to ensure that every phase is occurring to plan.
First checkpoint - end of G1
Cell growth is assessed and favorable conditions are checked. If this checkpoint fails, the cell enters G0, which is a non-dividing state. Some cells (liver, kidney) can be induced out of G0, while others (nerve, muscle) permanently reside in G0
Second checkpoint - end of G2
Checks for sufficient Mitosis Promoting Factor (MPF) levels to proceed to mitosis. The accuracy of DNA replication is also evaluated
Third checkpoint - M
Occurs during metaphase and checks if all chromosomes are attached to kinetochores. This also triggers the start of G1.
Cyclin-dependent kinases (CDK’s)
Activates ‘proteins that regulate the cell cycle’ via phosphorylation. Are activated by protein cyclins, which vary in type and concentration throughout each phase of the cell cycle
Growth factors
Plasma membrane contains receptors for growth factors that stimulate cell division, such as in a damaged cell
Density-dependent inhibition
Cells stop dividing when surrounding cells density is at a maximum
Anchorage dependence
Most cells only divide when they are attached to an external surface such as neighboring cells or placed on a culture dish
Transformed cells
Cancer cells that defy 4 conditions: CDK’s, growth factors, density-dependent inhibition, anchorage dependence. Cancer drugs also inhibit mitosis by disrupting the ability of microtubules to separate chromosomes during anaphase, thus stopping replication
Meiosis I
Reduction division; homologous chromosomes pair at the plate, migrate to opposite poles, yet there is no separation of sister chromatids
Prophase I
Nucleus disassembles, nucleolus disappears, nuclear envelope breaks down, chromatin condenses, and mitotic spindle develops. The microtubules begin attaching to kinetochores, and crossing over occurs, which allows for genetic recombination.
Prophase I - Synapsis
Occurs during prophase I, which involves homologous chromosomes pairing up, forming a tetrad (group of 4 chromatids) or bivalents
Prophase I - Chiasmata
Region where crossing over of non-sister chromatids occurs
Prophase I - Synaptonemal complex
Protein structure that temporarily forms between homologous chromosomes; gives rise to tetrad with chiasmata and crossing over
Prophase I - leptotene
Step 1/5 of prophase I. Chromosomes start condensing
Prophase I - zygotene
Step 2/5 of prophase I. Synapsis begins, synaptonemal complex forms
Prophase I - pachytene
Step 3/5 of prophase I. Synapsis complete, crossing over
Prophase I - diplotene
Step 4/5 of prophase I. Synaptonemal complex disappears, chiasma still present
Prophase I - diakinesis
Step 5/5 of prophase I. Nuclear envelope fragments, chromosomes complete condensing, and tetrads are ready for metaphase
Metaphase I
Homologous pairs line up along the metaphase plate, and microtubules attach to kinetochores of one member of each homologous pair.
Anaphase I
Homologues within tetrads uncouple and pulled opposite sides (disjunction)
Telophase I
Nuclear membrane develops and each pole forms a new nucleus that has half the number of chromosomes (from homologous pair to each chromosome = 2 sister chromatids). The cell is now haploid. Interphase may occur after telophase I, depending on the species
Meiosis II
Chromosomes lining up on the metaphase plate and sister chromatids separating and migrating to opposite poles; similar to mitosis
Prophase II
Nuclear envelope disappears and spindle develops, but no chiasmata or crossing over occurs
Metaphase II
Chromosomes align on metaphase plate like in mitosis, but now with half the number of chromosomes (no extra copy)
Anaphase II
Each chromosome is pulled into 2 separate chromatids and migrate to opposite poles of the cell. 46 chromosomes total in humans because the cell is not yet split
Telophase II
Nuclear envelope reappears and cytokinesis occurs → 4 haploid cells form, with each chromosome consisting of one chromatid
Fertilization/syngamy
Fusion of 2 haploid gametes, resulting in a diploid zygote
3 Genetic variation events
- Crossing over during prophase I
- Independent assortment of homologues during metaphase I; The entry of chromosomes into one cell does not affect entry of the other chromosome into the other cell
- Random joining of gametes, aka germ cells; The sperm randomly selects an egg to fertilize
Alternation of Generations
In plants, meiosis in sporangia produces spores (haploid), which undergo mitosis to become multicellular haploid gametophytes. These gametes fuse together to form a diploid zygote that grows via mitosis into a sporophyte. Cells in the sporophyte (sporangia) undergo meiosis again to produce haploid spores that germinate and repeat the life cycle known as alternation of generations.
2 Functional Limitations to Cell Division
2 main ratios that dictate if a cell will divide: Surface to volume ratio and Genome to volume ratio
Surface to volume ratio
As cells grow, the volume grows much larger compared to the surface area. When SA:V is large, exchange across the cell becomes much easier. When SA:V is small, exchange is harder, leading to either cell death or cell division to increase SA
Genome to volume ratio
Genome size remains constant throughout life, as cell growth leads to only an increase in volume. G:V will be small and thus exceed the ability of its genome to produce sufficient amounts of regulation of activities. Some large cells like paramecium and human skeletal muscle are multinucleate to deal with this.
Joining of gametes
Random, but some sperm cells contain genetic material that gives them a competitive advantage - so they all aren’t “equally” competitive
