BIOL 111 - Exam 2

Prokaryote

A microscopic, single-celled organism (bacteria, archaea etc.)

Nucleoid

Where DNA is located in prokaryotes

Peptidoglycan cell wall

A rigid layer surrounding bacterial cells, providing support and protection. Composed of alternating sugar chains linked by peptides

Pili

Help prokaryotes exchange genetic information during conjugation using plasmids; also help bacteria move

Flagella

Long, whip-like structures found in some cells that aid in movement. They are made up of microtubules and can be found in organisms like bacteria and sperm cells

Fimbriae

Short, hair-like structures found on the surface of some bacteria that help them attach to surfaces or other cells.

Bacterial resistance

Occurs because bacteria can exchange genetic information

Transduction

used to insert the genes of choices in animals & plant cells to modify their DNA & achieve desired characteristics. It can be used for gene therapy

Endosymbiosis

The hypothesis that mitochondria and chloroplasts originated as independent prokaryotic organisms.

Evidence for endosymbiosis

• Mitochondria and chloroplasts have their own DNA and ribosomes

• Mitochondria have a bacterial structure in their inner membrane and a eukaryotic structure in their outer membrane

• Mitochondria divide by a binary fission like mechanism like bacteria

Extracellular matrix

• A large network of proteins and other molecules that surround, support, and give structure to cells and tissues in the body

• Allows cells in tissue to communicate with each other

Secretory vesicles

Move molecules (signaling and functional) outside of the cell through exocytosis

Exocytosis

Vesicles fusing with the plasma membrane & releasing contents to the outside of the cell

Endocytosis

Capturing a substance or particle from outside the cell by engulfing it with the cell membrane

Intracellular junctions

• Direct channels of communication between cells

• Connect plasma membranes of adjacent cells

Tight junctions

• Watertight seals between 2 adjacent cells

• Proteins claudins and occludins hold the cells against each other

• Found in epithelial cells that line internal organs and cavities

Gap junctions

• Channels allow ions, nutrients and other small molecules to move between cells

• Develop when 6 proteins (connexins) form an elongated doughnut-like structure (connexon) in the plasma membrane

• Coordinates the activity of adjacent cells

• Important in cardiac muscles

Desmosomes

• Strong adhesions between cells in tissues that are under a lot of mechanical stress

• Maintains a sheet-like formation

• Includes cadherins, plaques and intermediate filaments

• Known as spot welds because they are tethered to the intermediate filament network

Where are tight junctions found?

Blood brain-barrier, bladder

Where are gap junctions found?

Cardiac muscles, nerves and smooth muscles in intenstines

Where are desmosomes found?

Cardiac cells, bladder, gastrointestinal tract, and epithelia

Plasmodesmata

• How plant cells communicate

• Transports water, nutrients and proteins

Apoplastic pathway

• Inside cell wall, outside plasma membrane

• Transports water

Symplastic pathway

• Cytoplasm to cytoplasm

• Transports metabolites and proteins

Cell membrane functions

• Defines cell borders

• Selectively permeable

• Must serve cell’s functions

• Carries surface markers

• Contains complex integral proteins

Components of the cell membrane

• Phospholipids

• Proteins

• Carbohydrates

Fluid mosaic model

A collections of cellular membrane components give the membrane a complete and fluid character

Membrane fluidity factors

• Temperature

• Cholesterol

• Unsaturated/saturated fats

Increases in membrane viscosity (thickness) →

disease states ( onset of atherosclerosis, malignancy, diabetes and hypercholesterolemia)

Increase in membrane fluidity (liquidity) →

effects on normal cell function via lipids in the membrane

Phospholipid head components

• glycerol molecule

• polar phosphate group

Phospholipid tail components

2 fatty acid chains (saturated and unsaturated)

Protein function in cell membranes

• Transporters

• Receptors

• Enzymes

• Binding and adhesion

Integral proteins

• Combined completely into the bilayer

• One or more hydrophobic regions

Peripheral proteins

Occur only on the surfaces

Carbohydrates

• Found on the exterior of the plasma membrane bound to proteins or lipids

• Function as labels and points of attachment for other cells

Passive transport

Cellular transport that does not require energy

Types of passive transport

• Diffusion

• Facilitated diffusion

• Osmosis

Active transport

Cellular transport that requires energy

Types of active transport

• Protein pumps

• Endocytosis

• Exocytosis

Osmosis

Diffusion of water across a membrane

Direction of osmosis

High water concentration → low water concentration

Aquaporins

Quickly transport water across a cell membrane (ex: liver, kidneys, lungs, eyes, etc.)

Tonicity

The ability of a solution to modify the volume of cells by altering their water content

Osmolarity

Total solute concentration of a solution

Hypotonic osmolarity

• Outside water concentration > inside water concentration

• Water moves inside

• Lysed cell

Isotonic osmolarity

• Outside water concentration = inside water concentration

• Equilibrium

• Normal cell

Hypertonic osmolarity

• Outside water concentration < inside water concentration

• Water moves outside

• Shriveled cell

Osmoregulation

The process by which organisms regulate the balance of water and solutes in their bodies to maintain internal stability

Osmoregulation in organisms with cell walls

• Prefer hypotonic extracellular solutions

• Turgor pressure

Plasmolysis

Process in which a plant cell loses water due to a hypertonic environment, causing the cell membrane to shrink away from the cell walld

Freshwater protist osmoregulation

Contractile vacuoles pump water out of the cell to prevent bursting

Molecules that can be passively transported

• O₂

• CO₂

• lipid hormones

Factors that increase diffusion rates

• Greater concentration gradient difference

• Smaller molecules

• Higher temperature

• Lower solvent density

• Nonpolar solutes

• Increased surface area

• Smaller distance traveled

• Greater cell pressure

Facilitated passive transport

Moves substances (ions and small polar molecules) down their concentration gradients using integral membrane proteins; energetically spontaneous

Channel protein

Passively transports ions and polar molecules; has a hydrophilic amino acids

Carrier protein

Passively transports glucose; changes shape

Function of active transport

• Moves substances against the concentration gradient

• Moves substances against its electrochemical gradient

Primary active transport

Active transport when ATP provides the energy to establish a gradient

Secondary active transport

Active transport when an electrochemical gradient provides the energy

Uniporter carrier protein

Carries one molecule or ion

Symporter carrier protein

Carries two different molecules or ions in the same direction

Antiporter carrier protein

Carries two different molecules or ions in different directions

Electrogenic pumps

• Primary active transport

• Generate voltage across the cell membrane

Sodium-potassium pump

• Primary active transport

• Pumps sodium out and potassium in; ratio of 3Na per 2K

• Nerve transmission

Proton pump

• Primary active transport

• Pushes protons across the membrane

When does secondary active transport happen?

When glucose is more concentrated inside than outside but the cell needs more glucose to meet its metabolic needs.

How is ATP made from using active transport?

Potential energy accumulated in stored hydrogen ions gets translated into kinetic energy when the ions move through the channel protein which is used to convert ADP into ATP

Endocytosis

Importing particles in bulk

Exocytosis

Exporting particles in bulk

Types of endocytosis

• Phagocytosis

• Pinocytosis

• Receptor mediated endocytosis

Phagocytosis

Cellular eating; a particle is surrounded and engulfed by the cell membrane

Pinocytosis

Cellular drinking; cell membrane forms a cavity, surrounds a fluid and pinches off

Receptor mediated endocytosis

Specific substances are targeted by binding receptors on the external surface of the membrane

Bioenergetics

The study of energy flow through living organisms

Metabolism

All chemical reactions taking place inside a cell that keep the body alive and healthy

1st Law of Thermodynamics

The total energy of an isolated system is constant; energy cannot be created nor destroyed, only transformed

2nd Law of Thermodynamics

Entropy constantly increases in a closed system

Potential energy

Electrochemical gradients across the plasma membrane

Kinetic energy

Energy released when a bond breaks

Anabolic pathway

• Small molecules are built into large ones

• Uses energy

• Endergonic

Catabolic pathway

• Large molecules are broken down into large ones

• Releases energy

• Exergonic

Gibbs free energy

Amount of energy available to perform work

Exergonic reactions

• ∆G<0; energy released

• Energy of products < energy of substrates

• Cellular respiration

Endergonic reactions

• ∆G>0; energy required

• Energy of products > energy of substrates

• Photosynthesis, Na-K pump

ATP energy coupling via phosphorylation

• ATP is hydrolyzed

• ATP phosphate transfers to another molecule

• Conformational change is induced

Endergonic and exergonic reaction relationship

• Energy released by exergonic is used for the endergonic reaction

• If not coupled, energy is lost as heat

Activation energy

• Energy required for a reaction to proceed

• Heat energy is the main source

Transition state

The state when reactants become unstable which allows bonds to be broken/made

Enzymes

• Biological catalysts

• Lower activation energy

• Very specific but recyclable

Enzyme specificity

The ability of an enzyme to select a specific substate from a range of chemically similar compounds

Active site

The location where the enzymes interacts with substrates

Induced fit

Mild shift in shape that triggers catalysis

How enzymes lower activation energy

• Positioning

• Optimal environment (temperature, pH)

• Contorting/stressing the substrate to make it less stable

• Temporarily reacting with substrate

Factors that regulate enzymes

• Changes in temperature or pH

• Production of molecules that can inhibit/promote enzyme function

• Availability of coenzymes or cofactors (enzyme helper molecules)

Competitive inhibitors

• Slow enzyme function

• Similar shape to the substrate

• Competition for substrate

Noncompetitive inhibitors

• Slow enzyme function

• Bind to enzyme at allosteric location (different location)

• Decreased affinity for the substrate

Positioning two substrates so they align perfectly for the reaction

Enzymes lowering activation energy

Providing an optimal environment (i.e. acidic or polar), within the active site for the reaction

Enzymes lowering activation energy

Contorting/stressing the substrate so it is less stable and more likely to react

Enzymes lowering activation energy