exam 2 - bio 311 c

what is the fluid mosaic model of membrane structure?

fluid=rapid movement of components, especially lipids

mosaic=irregular pattern of lipids and proteins

which makes membranes more fluid at room temperature?

unsaturated hydrocarbon tails - more fluid and flexible

how does cholesterol affect membrane fluidity?

low temp: increases fluidity (loosens packing)

high temp: decreases fluidity (stabilizes membrane)

name 2 molecules that can diffuse directly through the phospholipid bilayer

• small, uncharged polar molecules (ex: water (H2O)

• hydrophobic molecules (ex: O2, CO2, N2)

why can’t sodium ions diffuse by simple diffusion?

sodium ions are charged ions therefore they need a transport protein to diffuse

why can’t glucose diffuse by simple diffusion?

needs transport protein as it is large, uncharged polar molecule

simple diffusion

crosses membrane through phospholipid bilayer (high to low)

• no energy

facilitated diffusion

crosses membrane via protein channel/carrier (high to low)

• no energy

active transport

uses ATP to move against gradient (low to high) OR moving an ion to an area of its same charge (moving H+ to postive region)

down a gradient

net movement from high concentration to low concentration

across/against a gradient

net movement from low concentration to high concentration

a membrane has 0.5 M Na+ on side A and 0.2 M Na+ on side B. With Na+ channels, which way do ions move?

facilitated diffusion → high to low concentration

net movement from side A to side B

how do ion movements generate electrochemical gradients?

transport creates differences in ion concentration and charge driving further movement toward opposite charges

what is osmosis?

movement of water across semi-permeable membrane

what determines water movement across a membrane?

water moves toward higher solute concentration

what are aquaporins?

protein channels for water

facilitated diffusion → passive transport

how does the Na+/K+ pump work

uses 1 ATP to move Na+ OUT and K+ IN

in proton-sucrose co-transport, what drives sucrose uptake?

H+ gradient powers sucrose transport against its gradient (no ATP needed)

what happens to membrane potential when positive ions enter a cell?

membrane potential becomes less negative

resting membrane voltage inside of the cell

negative

depolarization

less negative → more excitable

hyperpolarization

more negative → less excitable

potential energy

chemical bond (stored) energy

heat energy

kinetic energy

energy of motion

entropy

measure of disorder/randomness

greater entropy means

more disorder

in ΔG = ΔH - T ΔS, what is ΔH?

ΔH = enthalpy

in ΔG = ΔH - T ΔS, what is ΔS?

ΔS = entropy

in ΔG = ΔH - T ΔS, what is ΔG?

ΔG = change in free energy

ΔH enthalpy

heat/chemical bond energy

ΔS entropy

disorder

ΔS increases (entropy)

ΔG decreases (free energy)

ΔH increases (enthalpy)

ΔG increases (free energy)

why does a system at the top have more free energy than at the bottom?

top: more potential energy, less stable, less entropy

bottom: more stable, less free energy, more entropy

endergonic

ΔG>0 (positive ΔG), energy absorbed, non-spontaneous.

exergonic

ΔG<0 (negative ΔG), energy released, spontaneous.

free energy/stable: ATP

• higher free energy

• less stable

free energy/stable: ADP

• lower free energy

• more stable

what are energy coupled reactions?

exergonic reaction energy is used to power an endergonic reaction → more efficient

how do enzymes lower activation energy?

use specific substrate binding to lower energy barrier without changing ΔG

how does protein structure affect enzyme specificity?

active site shape & R-group determine substrate binding

how does protein structure affect enzyme activity?

high temp or extreme pH can denature enzyme → loss of activity

how does increasing substrate concentration affect enzyme rate?

rate increases until enzymes are saturated, then levels off

competitive inhibitors

binds at the active site → substrate can NOT bind, reaction is inhibited

non-competitive inhibitors

does NOT bind at active site→ substrate can bind but reaction is inhibited

reaction pathway A→B→C→D needs how many enzymes?

3 enzymes (one per reaction step)

how does end-product feedback inhibition regulate pathways?

excess product inhibits pathway → prevents waste of resources, only produces what’s needed

End product feedback inhibition stops a pathway when there’s plenty of product. This prevents the cell from wasting energy and materials and only makes more when its needed.

oxidation

loss of electrons / 2 H+ atoms

reduction

gain of electrons / 2 H+ atoms

OIL RIG

oxidation is loss

reduction is gain

NAD molecule

dinucleotide (2 phosphate, 2 sugar, 2 bases) coenzyme

which is oxidized? more/less free energy?

NAD+ → less energy

which is reduced? more/less free energy?

NADH → more energy

glycolysis inputs

• glucose

• 2 ADP + P

• NAD+

glycolysis outputs

• pyruvate

• 2 ATP per glucose

• NADH

reduced product of glycolysis

NADH

oxidized product of glycolysis

pyruvate

why is citric acid cycle called a cycle?

end product regenerates starting molecule

oxidized product of citric acid cycle

• CO2

reduced products of citric acid cycle

• NADH

• FADH2

inputs of citric acid cycle

• acetyl (reduced carbon)

• ADP + P

• 1 FAD (oxidized carrier)

• 3 NAD (oxidized carrier)

outputs of citric acid cycle

• 2 CO2 (oxidized carbon)

• 2 ATP (1 per cycle, 2 per glucose)

• 1 FADH2 (reduced carrier)

• 3 NADH (reduced carrier)

inputs of electron transport chain

• NADH

• FADH

• O2

outputs of electron transport chain

• FAD

• NAD

• H2O

role of NAD/FAD as shuttles

shuttle electrons

• reduced in glycolysis/citric acid cycle

• oxidized in electron transport chain to power ATP production

location of glycolysis

cytosol

pyruvate → acetyl location

inside mitochondrion

location of citric acid cycle

mitochondrial matrix within the inner membrane

location of electron transport chain and ATP synthase

inner mitochondrial membrane

are redox reactions along electron transport chain exergonic or endergonic?

exergonic

where is o2 directly used?

o2 is used at end of electron transport chain

why does citric acid cycle (krebs) stop without O2?

citric acid cycle (krebs) stops without o2 because no NAD/FAD regenerated

what provides energy to build up a high concentration of H+ ions (proton gradient between inner and outer mitochondrial membranes?

energy coupled reactions

• exergonic: electron transport chain → releases energy

• endergonic: build H+ gradient → requires energy

what exergonic process powers ATP synthesis at ATP synthase?

H+ diffusing down gradient

energy from hydrocarbon chain of fats enters aerobic respiration and is used at what point?

citric acid cycle (krebs)

energy from the hydrocarbon chain of fats enters aerobic respiration as what molecule?

acetyl

why do cells ferment when no O2 is present

to regenerate NAD+ and keep glycolysis running

A respiratory “uncoupling agent” allows H⁺ ions to diffuse across the inner mitochondrial membrane at sites other than through ATP synthase. What is the effect on ATP production?

decrease in ATP production, because H⁺ ions are no longer moving through ATP synthase, so the proton gradient is not used to make ATP.

overall photosynthesis reaction

co2 + h2o + light → C6H12O6 + O2

main reduced product of photosynthesis

sugar (C6H12O6)

light reactions inputs

• h2o

• light

light reaction outputs

• ATP

• NADPH

• O2

calvin cycle inputs

• CO2

• ATP

• NADPH

calvin cycle outputs

• sugar

• ADP

• NADP

how are light reactions and calvin cycle linked?

light reactions provide ATP/NADPH; Calvin cycle regenerates ADP/NADP

how is ATP from light reactions used? (Las Vegas)

All ATP made in light reactions remains in chloroplast and is used to make sugars in Calvin cycle

what excites electrons in chlorophyll?

light energy

as electrons move through electron transport chain in thylakoid membrane what happens to H+ ions?

energy from electron movement powers a pump which pumps H+ ions from stroma into thylakoid lumen

energy coupled reaction: thylakoid membrane

exergonic: electron movement releases energy

endergonic: pumping H+ ions uses energy

what is direct source of energy for making ATP at ATP synthase in thylakoid membrane?

diffusion of H+ ions down their proton gradient through ATP synthase

in the linear (not a cycle) light reactions, what is the role of water (H2O)?

water provides electrons (H+) to refill chlorophyll after it loses electrons to the electron transport chain

how does NADP in photosynthesis act like NAD in respiration?

both are INPUTS for respective processes

both are electron carriers (oxidized carriers)

NADP in photosynthesis

accepts electrons and H+ to form NADPH

is light used directly in calvin cycle reactions?

no, it is not DIRECTLY used

why would the calvin cycle stop in absence of light?

calvin cycle stops without light because ATP and NADPH from light reactions are required for its reactions

ATP and NADPH = light reaction products & calvin cycle inputs

why isn’t all of reduced Calvin cycle product (G3P) used to make sugar immediately?

most G3P is recycled to regenerate RuBP, which allows the cycle to continue

function of RuBP

ensure the Calvin cycle continues

• ATP is consumed and converted into ADP + P; inputs of light reactions

what reaction does rubisco catalyze?

first reaction of Calvin cycle: fixation of CO2 (carbon dioxide)

what kind of inhibitor is O2 (in terms of rubisco/CO2 fixation)?

O2 binds to active site → competitive inhibitor

calvin cycle (3 parts)

1. CO2 fixation (add to a 5C-2P sugar RuBP)

2. “energize” 3-carbon sugar (using ATP) and reduce 3-carbon sugar (using NADPH)

3. take some G3P (sugar) product to make carbs

4. regenerate the start of next cycle (RuBP)