LSU Bio 1201 exam 2

why are membranes called phospholipid bilayers?

phospholipids have hydrophilic head and hydrophobic tail, hydrophobic face inside of cell making 2 layers

what is meant by fluid mosaic?

Mosaic of proteins drifting laterally in fluid bilayer of phospholipids

how are membranes adjusted for different temperatures?

membrane fluidity adjusted by changing the ratio of unsaturated to saturated fatty acids

how do the relative amounts of saturated and unsaturated fats change?

if you are in a cold environment you want more saturated fats for your membranes to be fluid; warm environment you want more saturated fats to make your membranes more solid

what is meant by membrane fluidity?

not too solid, not too fluid

why is fluidity an important property?

preserves membrane function

Henrique and Hanson performed experiments with pigs and examined the effects on the relative amounts of saturated and unsaturated fats. What did they find?

found that membrane fluidity can acclimate to temperature; pigs raised wearing underwear in a hot room had subcutaneous fats with higher melting point

what types of molecules can move easily across the membrane?

small nonpolar molecules, gases, steroid hormones, and water

what is simple diffusion?

down the concentration gradient; does not require supplied energy; does not use a carrier molecule

what is facilitated diffusion?

down the concentration gradient; employs carrier molecule; does not require supplied energy

what is active transport?

work must me done; must use supplied energy; employs carrier molecule

for which transport processes are carrier molecules involved?

facilitated diffusion and active transport

which transport processes require the input of additional energy?

active transport

what is a semi-permeable barrier?

only some types of molecules pass through

when equilibrium is reached in diffusion: does movement of molecules stop?

no

when equilibrium is reached in diffusion: does the net movement of molecules stop?

yes

what is meant by hypertonic?

lower water potential; more solutes dissolved; tend to gain water via osmosis

what is meant by hypertonic?

higher water potential; fewer solutes dissolved; will tend to lose water via osmosis

isotonic

equivalent water potential; equal number of solutes; no note movement of water

in which direction does water flow?

osmosis and the direction of net water movement

what are aquaporins?

channel proteins which facilitate water diffusion through the membrane

marine bony fish are...?

hypotonic to seawater

how do enzymes work?

they position the reactants in a conformation more favorable for the chemical reaction to occur

what aspects of the energetics do enzymes change?

enzymes lower activation energy barrier ΔG⧧

what aspects of energetics do enzymes not affect?

they do not reverse an energetically unfavorable reactions; they do not make a reaction go uphill

how are substrates lured into the active site?

positively charged arginine sidechain lures the negatively charged substrate into the active site

what are the analogs to these characters in the binding of substrates to enzymes?

Siren song= positively charged arginine sidechain

Negatively charged substrate= Odysseus' men

Circe= active site

how do temperature changes affect the rates of reactions catalyzed by enzymes?

temperature is a measure of how many molecules will have achieved activation energy; low temp= low energy associated with molecule

what is meant bby the thermostability of an enzyme?

Able to remain stable and function at high temperatures

Proteins can be denaturation by physical factors such as temperature and pH

Environment can alter enzyme's functional properties: denaturation

-Temperature

-Hydrogen ion concentration

-Solutes

-Hydrostatic pressure

What sets the upper temperature limit for life - the presence of liquid water or the stability of biological molecules?

Stability of biological molecules

At high temperatures biological molecules, such as protein and DNA, break down very rapidly

Why is there an upper limit?

It is energetically too costly to make biological molecules that breakdown that quickly

You can't build them faster than they are broken down

Enzyme homologs - what are they?

Comparable enzymes from different organisms

Enzyme homologs from cold- and warm-adapted species - how do they differ in order to adapt to the different thermal energy in their environments to maintain adequate catalytic rates?

At their respected temperatures the enzymes catalyze the reaction at similar rates

At a common temperature, the enzyme from cold-adapted species converts substrate to product a faster rate

Coenzymes

NAD (oxidized form)

NADH (reduced form)

NADP (oxidized form)

NADPH (reduced form)

FAD+

FADH2

What do we mean by "reducing power?"

The addition of electrons or hydrogen to a molecule (adds energy)

Oxidation= the removal of electrons or hydrogen from a molecule (reduces energy)

There is a constant pool cycling between the reduced and oxidized forms.

Competitive enzyme inhibition

Substrate and inhibitor compete for binding ot the active site of the enzyme

Inhibitor is structurally similar to the substrate

Most apparent at low [substrate]

Noncompetitive enzyme inhibition

Inhibitor binds at a site away from the substrate binding site

Causes a conformational change in the enzyme

Not overcome by increasing the [substrate]

Allosteric

"other site"

Modulator (activator or inhibitor) binds to a site other than the substrate binding site (active site)

Causes a conformational change of the enzyme which changes the activity

What is the role of inhibition in regulating metabolic pathways?

The product of a pathway may be very different from the starting material: won't be a good fit as a competitive inhibitor

Therefore inhibit at an "other site": allosteric inhibition

First Law of Thermodynamics

Within any closed system the total amount of energy remains constant

"Energy can be transferred and transformed, but it cannot be created or destroyed"

Second Law of Thermodynamics

All spontaneous processes resuilt in an increase in randomness and disorder in the universe and consequently In a loss of localized concentrations of energy

Entropy is a measure of disorder

What is the activation energy barrier (ΔG‡)?

The height of this barrier determines the rate of the reaction

Energy required for the favorable positioning of the reactant so the reaction can occur

How do enzymes affect catalytic rates (rate of conversion of substrate to product)?

Enzymes lower activation energy barrier

Enzymes speed up reaction 108-1020 times faster

What are the energy sources for burst activity?

Glucose

glycogen

Why is fat not used in anaerobic energy generation?

Fat mobilization requires O2

The high energy storage phosphagens in vertebrates and invertebrates are Creatine Phosphate and Arginine Phosphate, respectively. What their role is in energy metabolism?

Creatine Phosphate recharges ADP back to ATP

What is a kinase?

Catalyzes the transfer of a higher energy phosphate to generate ATP

In plants, where is ATP synthase located?

Thylakoid membrane and inner mitochondrial membrane

Where does the Calvin-Benson cycle occur?

Stroma of chloroplasts

The light reactions produce

ATP, NADPH, O2

What would happen to red blood cells if they were placed in a hypotonic solution?

They would lyse (explode)

What step in a metabolic pathway is it energetically most desirable to inhibit?

The first enzyme in the pathway

What type of enzyme regulation is pictured?

Competitive

Which contains more energy: NADH or FADH2?

NADH

Which contains more energy: Glucose or pyruvate?

Glucose

O2 is used by

Oxidative phosphorylation

O2 is produced by

Light reactions

Water is split in

Light reactions

Autotroph

An organism that obtains organic molecules without eating other organisms

Heterotroph

An organism that obtains organic molecules by eating other organisms

An endergonic reaction has negative or positive ΔG?

Positive (+ ΔG)

What is ΔG‡?

Activation energy barrier; determines the rate of the reaction

Is a reaction with - ΔG spontaneous?

yes

What bonds are broken during protein denaturation?

Protein unfolds due to broken weak bonds which stabilize the 3-dimensional structure

What is the energy currency of cells?

ATP

Which type of inhibition can be overcome by increasing substrate concentration?

competitive

What step in a metabolic pathway is it energetically most desirable to inhibit?

The first enzyme in the pathway

How many ATPs (net) are produced in glycolysis using glucose as the starting material?

2

Where does glycolysis occur?

cytoplasm

What are the products from the glycolysis of 1 glucose molecule?

2 ATP, 2 NADH, 2 pyruvate

Of glucose, ATP, pyruvate, and NADH, which has the most energy?

Glucose

What enzymes catalyze substrate level ATP production?

Kinases

Where in the cell does the ETC and chemiosmosis take place?

mitochondria

Creatine Phosphate - high energy phosphagen store in

vertebrates

Arginine Phosphate - high energy phosphagen store in

invertebrates

The high energy phosphagen store is used to regenerate

ATP

Catabolic processes (produce or require?) ATP and reducing power

produce

Anabolic processes (produce or require?) ATP and reducing power

require

In the (presence or absence?) of adequate oxygen, glucose is fermented in the cytoplasm

absence

In the (presence or absence?) of adequate oxygen pyruvate is channeled into the Krebs cycle in mitochondria.

presence

The free energy of the proton gradient is used to drive the synthesis of ATP which is

an exergonic reaction catalyzed by the enzymes ATP synthase

how many ATP are produced in aerobic respiration?

net of 30-32

Chemiosmosis

the movement of protons down their concentration gradient to provide the energy for ATP synthesis

Which of the following statements about the role of phospholipids in forming membranes is correct?

Phospholipids form a selectively permeable structure.

The plasma membrane is referred to as a "fluid mosaic" structure. Which of the following statements is true?

The fluid component of the membrane is phospholipid, and the mosaic is protein

Which one of the following statements is true about diffusion?

Which one of the following statements is true about diffusion?

Which of the following statements is true about passive transport?

Passive transport permits the transported molecule to move in either direction, but the majority of transport occurs down the concentration gradient of the molecule.

Cells A and B are the same size, shape, and temperature, but cell A is metabolically quiet and cell B is actively consuming oxygen. Oxygen will diffuse more quickly into cell _____ because _____.

B ... the diffusion gradient in cell B is steeper

When 1 mole of ATP is hydrolyzed in a test tube without an enzyme, about twice as much heat is given off as when 1 mole of ATP is hydrolyzed in a cell. Which of the following best explains these observations?

In the cell, the hydrolysis of ATP is coupled to other endergonic reactions

The formation of glucose-6-phosphate from glucose is an endergonic reaction and is coupled to which of the following reactions or pathways?

the hydrolysis of ATP

The mechanism of enzyme action is _____.

lowering the energy of activation for a reaction

A chemical reaction is designated as exergonic rather than endergonic when _____

the potential energy of the products is less than the potential energy of the reactants

What best characterizes the role of ATP in cellular metabolism?

The free energy released by ATP hydrolysis may be coupled to an endergonic process via the formation of a phosphorylated intermediate.

A chemical reaction is designated as endergonic rather than exergonic when _____.

the potential energy of the reactants is less than the potential energy of the products

Which of the following statements about enzymes is true?

Enzymes speed up the rate of the reaction without changing the Delta G for the reaction.

A glucose molecule is completely broken down to carbon dioxide and water in glycolysis and the citric acid cycle, but together these two processes yield only a few molecules of ATP. What happened to most of the energy that the cell obtains from the oxidation of glucose?

It is stored in NADH.

In fermentation, ________ is ________.

NADH; oxidized

In the absence of oxygen, what is the net gain of ATP for each glucose molecule that enters glycolysis?

2 ATP

Pyruvate is formed

in the cytosol