Biology Chapter on Membrane Fluidity and Diffusion

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Questions and Answers

What is a characteristic feature of disaccharides?

They can only consist of pentose sugars.

They are formed through a condensation reaction that releases a water molecule. (correct)

They always take a linear structure.

They are always made of three monosaccharides.

What distinguishes aldose sugars from ketose sugars?

Aldose sugars have a carbonyl group at the end of the carbon chain. (correct)

Aldose sugars are exclusively found in polysaccharides.

Aldose sugars have a ketone group, while ketose sugars have an aldehyde group.

Aldose sugars contain multiple hydroxyl groups only.

Which of the following best describes the structure of starch?

It consists of glucagon molecules linked together.

It acts only as a structural component in plants.

It is a highly branched polymer of glucose with 1-4 and 1-6 linkages. (correct)

It is a linear polymer of glucose with no branching.

What role does glycogen serve in animals?

It is the main carbohydrate energy source found in muscle and liver cells. Signup and view all the answers

What effect can a low carbohydrate diet have on humans?

It can result in weakness and fatigue due to depleted glycogen stores. Signup and view all the answers

What effect do steroids have on membrane fluidity at high temperatures?

They decrease lipid movement, restraining the membrane's fluidity. Signup and view all the answers

How does temperature affect the packing of phospholipids in membranes?

Cold temperatures cause phospholipids to pack tightly together. Signup and view all the answers

What is the process by which water diffuses across a selectively permeable membrane called?

Osmosis Signup and view all the answers

What adaptation might a fish living in extreme cold have regarding its membrane composition?

A high proportion of unsaturated hydrocarbons. Signup and view all the answers

What characterizes tonicity in relation to cell water movement?

The ability of a surrounding solution to cause a cell to gain or lose water. Signup and view all the answers

What is the primary role of NAD+ in cellular respiration?

To carry electrons from one molecule to another Signup and view all the answers

During glycolysis, what is the net yield of ATP and NADH produced?

2 ATP and 2 NADH Signup and view all the answers

Which of the following accurately describes the citric acid cycle?

It generates CO2 and reduces NAD+ to NADH. Signup and view all the answers

What occurs during pyruvate oxidation before entering the citric acid cycle?

A carboxyl group is removed, and CoA is attached to form acetyl CoA. Signup and view all the answers

What effect does an increase in temperature have on proteins?

It causes proteins to denature. Signup and view all the answers

Which term describes the process of generating ATP by transferring a phosphate group from a substrate to ADP?

Substrate-level phosphorylation Signup and view all the answers

How do competitive inhibitors affect enzyme activity?

They reduce the productivity of enzymes by blocking substrates from entering the active sites. Signup and view all the answers

What role do cofactors play in enzymatic activity?

They are necessary for catalytic activity. Signup and view all the answers

What is allosteric regulation?

The binding of a regulatory molecule to a site other than the active site. Signup and view all the answers

What is the primary function of feedback inhibition in metabolic pathways?

To halt the pathway when sufficient product is made. Signup and view all the answers

What happens during cooperativity in allosteric enzymes?

Binding of one substrate increases the likelihood of additional substrates binding. Signup and view all the answers

Which of the following best describes non-competitive inhibitors?

They bind to a site other than the active site and change enzyme shape. Signup and view all the answers

What is a common characteristic of enzymes localized within cellular organelles?

They may serve as structural components of membranes. Signup and view all the answers

What type of respiration uses an electron transport chain without oxygen as a terminal electron acceptor?

Anaerobic respiration Signup and view all the answers

Which process generates 2 ATP through the oxidation of glucose without utilizing an electron transport chain?

Alcohol fermentation Signup and view all the answers

Which statement accurately describes the function of NAD+ in fermentation processes?

NAD+ acts as an oxidizing agent to accept electrons. Signup and view all the answers

Which of the following accurately characterizes lactic acid fermentation?

Leads to the conversion of pyruvate to lactate. Signup and view all the answers

Which class of organisms can survive both in the presence and absence of oxygen and can switch between aerobic respiration and fermentation?

Facultative anaerobes Signup and view all the answers

What is the primary purpose of glycolysis in both aerobic and anaerobic respiration?

To oxidize glucose to pyruvate. Signup and view all the answers

How much ATP is produced through fermentation compared to cellular respiration?

Fermentation produces 2 ATP while cellular respiration can produce up to 32 ATP. Signup and view all the answers

Why is glycolysis considered significant in the history of life?

It is the most widespread metabolic pathway and predates the use of oxygen. Signup and view all the answers

Study Notes

Membrane Fluidity

Membranes solidify at low temperatures.
Membrane fluidity depends on the types of fatty acid chains within phospholipids.
Cholesterol can insert between phospholipids to affect fluidity, acting as a buffer.
At high temperatures, cholesterol restrains lipid movement.
At low temperatures, cholesterol hinders close packing of phospholipids, preventing solidification.
Organisms adapt membrane fluidity to meet their specific environmental needs.
For example, fish in cold water have a higher proportion of unsaturated hydrocarbons.
Prokaryotes in hot springs have unusual lipids that prevent excessive fluidity.
Plants increase the percentage of unsaturated phospholipids in autumn to tolerate extreme cold.

Diffusion

Diffusion is the movement of a substance down its concentration gradient: from high to low concentration.
A spontaneous process that requires no energy input.
For example, oxygen diffuses into cells across the plasma membrane.

Osmosis

Diffusion of water across a selectively permeable membrane.
Water moves from areas of high free water concentration (low solute) to areas of low free water concentration (high solute).

Tonicity

Refers to the ability of a surrounding solution to cause a cell to gain or lose water.

pH

Enzymes are affected by acidic or basic environments.
H+ and OH- ions interact with chemical groups on amino acids.

Cofactors

Non-protein helpers required for catalytic activity.
Examples include:
- Zinc, iron, copper (inorganic)
- Vitamins (coenzymes, organic)

Enzyme Inhibitors

Some inhibitors bind covalently, often irreversibly.
Some inhibitors bind weakly, often reversibly.
Competitive inhibitors block substrates from entering the active site of an enzyme.
Competitive inhibition can be overcome by increasing substrate concentration.
Non-competitive inhibitors bind to a different part of the enzyme, causing it to change shape.
This change in shape makes the active site less effective.

Allosteric Regulation of Enzymes

Allosteric regulation occurs when a regulatory molecule binds to a separate site on a protein, affecting its function at another site.
Most allosterically regulated enzymes have multiple subunits.
The enzyme oscillates between active and inactive shapes.
Activators stabilize the active form of the enzyme.
Inhibitors stabilize the inactive form of the enzyme.

Cooperativity

A type of allosteric activation.
Binding of a substrate molecule to one active site in a multi-subunit enzyme triggers a shape change in all subunits, increasing catalytic activity at other active sites.
Cooperativity amplifies the enzyme's response to substrates.

Feedback Inhibition

The product of a metabolic pathway inhibits an enzyme that acts early in the pathway.
This prevents the cell from wasting resources when enough product exists.
Allosteric inhibition of the enzyme by the final product of the reactions.

Localization of Enzymes

Teams of enzymes in a metabolic pathway can be arranged into a multienzyme complex.
Some enzymes are embedded within membranes.
Others are found in solution within membrane-enclosed eukaryotic organelles.

Monosaccharides

Simple sugars with molecular formulas that are multiples of CH2O.
Contain:
- A carbonyl group
- Multiple hydroxyl groups
Depending on the carbonyl group position, it can be an:
- Aldose sugar (aldehyde)
- Ketose sugar (ketone)
Most sugars are hexoses, but trioses and pentoses are also common.
Isomers exist due to the placement of groups around asymmetric carbons.
Sugars exist in both linear and ring forms.
Most pentoses and hexoses form ring structures, which are more stable than linear structures.

Disaccharides

Two monosaccharides joined by a glycosidic linkage using a dehydration reaction.
Examples include:
- Maltose (2 glucose molecules)
- Sucrose (glucose + fructose)
- Lactose (glucose + galactose)
Lactose intolerance results from a lack of the lactase enzyme.

Polysaccharides

Hundreds or thousands of monosaccharides joined by glycosidic linkages.
Functions include:
- Storage (starch, glycogen)
- Building materials (cellulose, chitin)

Starch

Storage molecule in plants.
Found in granules inside plant plastids (amyloplasts).
Polymer of glucose monomers joined by 1-4 linkages.
Branching points are formed by 1-6 linkages.

Glycogen

Storage molecule in animals.
Found in liver and muscle cells.
Branched polymer of glucose like starch.
Branched structures offer more free ends available for hydrolysis.
Human glycogen stores last about a day unless replenished by eating.
Low-carbohydrate diets can lead to weakness and fatigue.

Cellular Respiration: A Redox Reaction

Oxidation of organic fuel molecules (loss of hydrogen).
Reduction of oxygen (gain of hydrogen).
Electrons lose potential energy, releasing energy.
Transfer of hydrogen atoms (one proton, one electron).

NAD+ Reduction to NADH

Glucose is progressively broken down in cellular respiration.
Electrons are removed in a series of steps.
NAD+ (nicotinamide adenine dinucleotide) is a coenzyme that carries electrons from one molecule to another.
NAD+ is reduced to NADH.

Stages of Cellular Respiration

Substrate-level phosphorylation: A phosphate group is transferred from a substrate to ADP, creating ATP. This occurs in both glycolysis and the citric acid cycle.

Stage 1: Glycolysis

Glucose is split into two three-carbon sugars (pyruvate).
Energy investment phase: ATP is used.
Energy payoff phase: ATP is produced by substrate-level phosphorylation, and NAD+ is reduced to NADH.
Net yield: 2 ATP and 2 NADH.

Stage 2: Pyruvate Oxidation and the Citric Acid Cycle

Pyruvate oxidation:
- Pyruvate enters mitochondria (in eukaryotes).
- Carboxyl group is removed (CO2 is released).
- Carbon is oxidized to form acetate.
- Coenzyme A is attached to acetate, forming acetyl CoA.
  - CoA is made from vitamin B.
Citric acid cycle:
- Also known as the tricarboxylic acid (TCA) cycle or Krebs cycle.
- Acetyl CoA is oxidized to CO2.
- Each cycle generates:
  - 1 ATP
  - 3 NADH
  - 1 FADH2
  - 2 CO2
- Acetate binds to oxaloacetate to form citrate.
- Two carbon atoms are released as CO2 molecules.
- Oxaloacetate is regenerated to be used again.

Anaerobic Respiration

Uses an electron transport chain.
Occurs in some prokaryotes living in anaerobic environments.
Instead of oxygen, a different molecule serves as the final electron acceptor.
Example: Sulfate-reducing bacteria use SO42- to produce H2S as a byproduct.

Fermentation

Does NOT use an electron transport chain.
Organisms use glycolysis for energy production (2 ATP).
Glycolysis produces NADH.
NADH is recycled back to NAD+ by transferring electrons to pyruvate.

Alcohol Fermentation:

Pyruvate is converted to ethanol.
CO2 is released.
Carried out by many bacteria and yeast.
Used in brewing, winemaking, and baking.

Lactic Acid Fermentation

Pyruvate is reduced to lactate.
Carried out by some fungi and bacteria.
Used in cheese and yogurt production.
Occurs in human muscle cells under oxygen-limited conditions.
Excess lactate is transported to the liver for conversion back to pyruvate.

Fermentation/Anaerobic Respiration: Similarities

Both produce ATP from food.
Both use glycolysis to oxidize glucose and other fuels to pyruvate.
Both rely on NAD+ as the oxidizing agent.

Fermentation/Anaerobic Respiration: Differences

The mechanism for NADH recycling to NAD+.
Amount of ATP produced (fermentation: 2 ATP; cellular respiration: up to 32 ATP).

Classes of Organisms

Obligate aerobes: Require oxygen for survival (only perform aerobic respiration).
Obligate anaerobes: Cannot survive in the presence of oxygen (only ferment or perform anaerobic respiration).
Facultative anaerobes: Can survive with or without oxygen:
- In the presence of oxygen, they perform aerobic respiration.
- In the absence of oxygen, they ferment.

Evolution of Glycolysis

Glycolysis is the first stage of aerobic, anaerobic respiration, and fermentation.
It is believed to have been used by ancient prokaryotes to generate ATP before oxygen was present in the atmosphere.
It is the most widespread metabolic pathway on Earth, suggesting an early evolution.
It occurs in the cytosol, requiring no membrane-bound organelles.

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Explore the fascinating concepts of membrane fluidity and diffusion in this quiz. Understand how factors like temperature and lipid composition affect membrane behavior and learn about the spontaneous process of diffusion across membranes. Challenge yourself with questions that cover various biological adaptations related to these topics.