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Membrane Structure and Function, Exams of Biology

Liberty University (LU)Biology

An overview of the structure and function of biological membranes, including the fluid mosaic model, membrane fluidity, and different types of membrane transport processes. It discusses how membranes adapt to different temperatures, the role of phospholipids and proteins in membrane structure, and the movement of various molecules across the membrane. The document also covers topics related to enzyme function, energy metabolism, and the thermodynamics of biological systems. Overall, this document covers a wide range of fundamental concepts in cell biology and biochemistry, making it a potentially useful resource for students studying these subjects at the university level.

Typology: Exams

2024/2025

Available from 10/12/2024

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LSU Bio 1201 exam 2 written solution
update
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
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LSU Bio 1201 exam 2 written solution

update

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

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+ FADH 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 O 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

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

Which statement about the citric acid cycle is incorrect? - The oxidation of compounds by the citric acid cycle requires molecular oxygen Cells do not catabolize carbon dioxide because - CO2 is already completely oxidized Most CO2 from catabolism is released during - the citric acid cycle Most of the energy that enters electron transport enters as - FADH2 and NADH Which of the following statements about the redox reactions of the electron - The redox reactions of the electron transport chain are directly coupled to the movement of protons across a membrane In the combined processes of glycolysis and cellular respiration, what is consumed and what is produced? - Glucose is consumed, and carbon dioxide is produced