gen bio outline 6 & 7 (membrane & transport, metabolism)

Membrane Components

• Membrane protein

• Carbohydrates

• But PRIMARLY phospholipids

Bilayer formation

• forms spontaneously

• amphipathic nature (hydrophobic+hydrophilic) due to phospholipid shape

• held together by hydrophobic interactions (van der wals)

Phospholipids

• Main Structural component of membranes

• Gylerol + 2 fatty acid tails (hydrophobic) + phosphate-head group (hydrophilic)

• Forms a phospholipid bilayer

Membrane proteins

• determine many membrane functions

• can be on one side or transmembrane (span across the membrane)

• Some move within the membrane

• Some cannot move

• amphipathic nature

Why can’t some membrane proteins move?

Attached to ECM (extracellular matrix) or cytoskeleton

Membrane protein FUNCTIONS:

• transport

• enzyme activity

• signaling/communication

• cell-to-cell recognition

• attachment to cytoskeleton & ECM

• structure

Carbohydrates

• polysaccharides attached to protein (glycoprotein) or lipid (glycolipid)

• primarily cell identification

Fluid Mosaic Model

fluid-membrane components can move laterally within the membrane

Mosaic-emergent properties of the membrane as a whole due to the combination and arrangement of components

Membrane Transport

• plasma membrane is selectively permeable (only some molecules can go through)

• 2 types of transport

Passive Transport

• does NOT need metabolic energy (ATP)

• net movement down a concentration gradient (molecules travel spontaneously from a highly crowded area to a less crowded area)

• simple diffusion, osmosis, facilitated diffusion

• results in dynamic equilibrium

Diffusion

tendency for molecules of a substance to fill an available space due to random constant molecule motion

What can diffuse directly across a membrane?

• small nonpolar molecules

• VERY small polar molecules

  • ex: gas, H₂O, small hydrocarbons

• No ions or charged molecules AT ALL

Dynamic Equilibrium

no NET movement at equilibrium; reactions do NOT stop; molecules keep changing back and forth. (ex: water bottle; water evaporates into gas and condenses back into liquid at the same speed)

Osmosis

diffusion of water across selectively permeable membrane

Solvent

a substance capable of dissolving other substances, the medium in which something is dissolved (ex: water)

Solute

a dissolved substance (ex: salt)

Direction of osmosis determined by…

difference in total solute concentration

Water diffuses from:

Lower solute concentration to higher solute concentration

Tonicity

ability of a solution to cause a cell to gain or lose water

Isotonic

solute concentration outside = solute concentration inside

no net H₂O movement (water molecules flow into and out of a cell at exact same rate, so cell stays the same size and does not swell or shrink)

Hypertonic solution

solute concentration outside > solute concentration inside

cell loses H₂O

Hypotonic solution

solute concentration outside < solute concentration inside

cell gains H₂O

What can’t diffuse directly across a membrane?

• Large molecules (too big)

• Ions and anything charged (even H+)

• Non-small polar molecules (even a lil bigger than H2O)

Faciltated Diffusion

• passive transport through a transport protein

• Doesn’t need ATP

• Transport protein specific to the substance that’s transported

• 2 types

  • channel (no change in shape)

  • carrier (change in shape)

Active Transport

• requires ATP

• works against concentration gradient (building the gradient, moving molecules from a less crowded area to a highly crowded area)

• Transport through a carrier protein

• ex: sodium-potassium pump

Sodium-Potassium Pump

• each cycle requieres one ATP

• Using energy to build gradients

Bulk transport

• transport many molecules at once using vesicles

• not carrier mediated, type of active transport; always requires ATP

• enter/exit cell WITHOUT crossing bilayer

Exocytosis

• Vesicle containing water/secretory products fuses with plasma membrane

• releases content form cell

• adds lipids to plasma membrane (primary mechanism to grow plasma membr.)

Endocytosis

• materials taken into the cell by forming vesicles from the plasma membrane

• Phagocytosis and Pinocytosis

(cells swallow large things outside of them by wrapping their outer skin around the material to bring it inside- folding the plasma membrane inwards)

Phagocytosis

large food particles, bacteria-eating

Pinocytosis

fluids and dissolved molecules, cellular-drinking

Metabolism

Sum of all chemical reactions and energy transformations in an organism

• emergent property of life

• regulated to maintain homeostasis

Metabolic Pathways

• series of chemical reactions, each involves energy transformation

• each step catalyzed(stimulated) by specific enzyme

Anabolic pathway

• synthetic, requires energy—making new bonds

• simple molecules → complex molecules

  • builds larger molecules from smaller ones

• ex: making polypeptide from amino acids

Catabolic pathways

• break bonds, releases energy—large molecules are broken into smaller ones

• complex molecule → simple molecules

• ex: cellular respiration

energy (E)

the capacity to do work (or supply heat), 2 forms of energy

Kinetic

energy of motion

Potential

stored energy, the capacity to do work

1st law of thermodynamics

Energy cannot be created nor destroyed, only converted from one form to another—”principle of conservations of energy”

2nd law of thermodynamics

every energy transfer or transformation increases entropy in the universe

Entropy (S)

measure of disorder, randomness; represents energy that isn’t usable—disperses into the environment

ex: heat released during respiration

Energy flow through ecosystems

• series of energy conversions

• (source of E) sun →stored as chemical E → converted to ATP → ultimately lost as heat

• no conversion is 100% efficient

  • Car internal combustion engine ~20-30% efficient

  • Cells ~40% efficient

Free energy (G)

• energy available to do work— E we can use

• can’t measure directly, can measure change (△G)

Free energy in cells:

• potential E stored in covalent bond:

  • Build new bonds → store E = +△G

• kinetic E released when bonds are broken:

  • Break bonds → release E = -△G

exergonic (catabolic)

• -△G

• E released

• spontaneous, just happens, no E required

endergonic (anabolic)

• +△G

• E stored

• not spontaneous, requires E input

Adenosine triphosphate

• high-energy molecule (3 phosphate groups)

• primary energy molecule of the cell

How do cells use ATP?

• coupled reactions

• pair endergonic reaction (requires E) with exergonic reaction (provides the E)

  • exergonic reaction often involves ATP hydrolysis

Exergonic reactions need…

often too slow to be useful so need a catalyst—chemical that speeds a reactions w/o being consumed

Enzymes decrease Activation Energy

• initial energy needed to start a reaction

• Causes reaction to occur faster – cannot cause reaction that wouldn’t happen anyway

Enzyme structure

• globular proteins

• substrate

• enzymes are specific

Enzyme function

enzymes work by forming enzyme substrate complex (attaching to specific molecule)

globular proteins

• often have grooves due to 3° or 4° structure

• Active site: region that interacts with the substrate

substrate

any substance acted upon by an enzyme

Induced Fit

enzyme changes shape slightly after binding to substrate for better fit, causes slight change in substrate, facilitates breaking/forming bonds

Why redox reactions matter?

make bonds → store E; break bonds → releases E

(Breaking bonds always requires energy, while making bonds always releases energy)

requires: electron transfer

Redox Reactions

• involve the movement/tranfer of an electron (e^-)

• Oxidation and reduction always happen together

• electrons alone are difficult to remove from covalent compound

Oxidation

donating an electron (losing e^-)

Reduction

accepting an electron (gaining e^-)

Oxidizing agent

e^- acceptor, becomes reduced

Reducing agent

e^- donor, becomes oxidized

A⁺ is ___ and B^- is ___

Oxidized, Reduced

A^o is ___ and B^o is ___

reducing agent, oxidizing agent