Cell Membrane Functions, Structure, and Transport Mechanisms in Biology

What is the major function of the plasma membrane?

To regulate the movement of substances into and out of the cell.

What is the composition of the plasma membrane?

Primarily a phospholipid bilayer and specialized proteins.

What is a phospholipid?

A lipid molecule made of glycerol, two fatty acid chains, and a phosphate-containing group.

What does the hydrophilic head of a phospholipid do?

It interacts with water.

What does the hydrophobic tail of a phospholipid do?

It repels water.

What affects the rate of diffusion?

Size, charge, lipid solubility, and concentration.

What happens to a cell in a hypotonic solution?

Water rushes into the cell, causing it to swell and possibly burst.

What is turgor pressure?

The pressure that keeps plant cells erect, resulting from swelling in a hypotonic solution.

What is active transport?

The movement of substances against their concentration gradient using energy (ATP).

What are proton pumps responsible for?

Moving hydrogen ions (H+) into the lumen of the stomach.

What is passive transport?

Movement of substances through the plasma membrane without using cellular energy (ATP).

What is diffusion?

The random movement of molecules from regions of greater concentration to regions of lesser concentration.

What is osmosis?

The diffusion of water across plasma membranes.

What is facilitated diffusion?

The passive movement of molecules across the cell membrane via membrane proteins.

What is filtration in the context of passive transport?

Movement of water and molecules across the cell membrane due to hydrostatic pressure.

What is a hypotonic solution?

A solution with a lower concentration of solute relative to the inside of a cell.

What is cytolysis?

The bursting of cells in a hypotonic solution.

What is a hypertonic solution?

A solution with a higher concentration of solute relative to the inside of a cell.

What is an isotonic solution?

A solution that has the same concentration of solutes as the inside of a cell.

What is endocytosis?

Transport of solid substances into a cell.

What is phagocytosis?

A form of endocytosis known as 'cellular eating'.

What is pinocytosis?

A form of endocytosis known as 'cellular drinking'.

What is exocytosis?

Transport of substances out of a cell that are too large to be transported through the membrane.

What is metabolism?

The sum total of chemical processes within an organism.

catabolic

Processes that break down substances.

What are anabolic processes?

Processes that build new substances.

What controls most chemical reactions within an organism?

Specialized proteins called enzymes.

What is an enzyme?

A biological catalyst that accelerates a chemical reaction without being affected by it.

How do enzymes improve metabolic efficiency?

By lowering the energy of activation required to initiate a reaction.

What are two physical means of attaining activation energy?

Heat and agitation.

What is a substrate?

The reactant that an enzyme works upon.

What is the active site of an enzyme?

The portion of the enzyme that binds to the substrate.

What is an enzyme-substrate complex?

The structure formed when an enzyme and substrate join.

How are enzymes reusable?

The product is released from the enzyme, freeing it to react with another substrate.

What type of chemical bond binds the substrate to the enzyme?

Usually weak ionic or hydrogen bonds.

What is the induced fit model?

It explains how an active site on an enzyme changes its shape slightly to accommodate the substrate.

Enzyme names usually end in what suffix?

-ase, such as sucrase and amylase.

Name one metabolically important enzyme in vertebrate RBCs.

Carbonic anhydrase.

What are cofactors?

Usually nonorganic metal ions such as copper, zinc, and manganese that aid the action of an enzyme.

What are coenzymes?

Nonprotein organic molecules that improve enzymatic action.

Name an important coenzyme involved in energy metabolism.

Nicotinamide adenine dinucleotide (NAD).

What factors can affect enzymatic action?

Concentration of substrate, concentration of enzymes, temperature, pH, salinity.

What are optimal conditions for enzymes?

The parameters within which enzymes work best.

What is the optimal temperature for most human enzymes?

Most human enzymes are more efficient near 37°C.

What is the optimal pH for most human enzymes?

Between 6 and 8, except for pepsin which works at pH 2.

What happens if the shape of an enzyme is altered?

The enzyme is said to have been denatured.

What are enzymatic inhibitors?

Substances that bind to an enzyme and decrease its activity.

What are enzymatic activators?

Substances that increase enzyme activity, including coenzymes and cofactors.

What is bromelain?

An enzyme produced by pineapple that breaks down proteins.

What happens to bromelain when pineapple juice is canned?

It is denatured.

What enzyme breaks down hydrogen peroxide?

Catalase.

What enzyme helps young mammals digest milk?

Rennilase (also known as rennin or chymosin).

Where is rennin produced?

In the stomach of newborn infants.

What does rennin do?

It converts milk protein (casein) to insoluble paracasein.

What does bacterial protease do to proteins?

Breaks them down into their component amino acids.

What indicator turns purple/blue in the presence of amino acids?

Ninhydrin.

How do enzymes make metabolism function more efficiently?

By lowering the energy of activation.

What is the substrate?

The reactant that the enzyme works upon.

What makes an enzyme substrate-specific?

The enzyme's unique 3-D molecular conformation.

What is formed when the enzyme and substrate join?

An enzyme-substrate complex.

What happens to the enzyme-substrate complex?

Catalytic actions convert it into one or more products.

Where does the substrate bind to the enzyme?

At the active site.

What is the difference between anaerobic and aerobic cellular respiration?

The final electron acceptor.

What is the equation for cellular respiration?

C6H12O6 + 6 O2 → 6 CO2 + 6 H2O

What is the first sequence of reactions in glucose energy release?

Glycolysis

What are the major end products of glycolysis?

Two ATP, two NADH, and two pyruvate.

What happens to pyruvate in the absence of oxygen?

They are metabolized via anaerobic fermentation.

What is another name for the Krebs cycle?

Citric Acid Cycle

What is the purpose of fermentation?

Production of ATP and regeneration of NAD+.

What is the waste product of alcoholic fermentation?

Ethanol

What is the end product of lactic acid fermentation?

Lactic acid (lactate)

How much ATP does fermentation usually produce?

4 ATP

Where does the carbon dioxide you exhale come from?

Pyruvate processing

Where does the Krebs cycle occur?

In the matrix of the mitochondrion.

What are the end products of the citric acid cycle per glucose molecule?

Two ATP, four CO2, six NADH, and two FADH2.

What are the steps of the Krebs cycle?

1. Citrate synthase, 2. Aconitase, 3. Isocitrate dehydrogenase, 4. α-ketoglutarate dehydrogenase, 5. Succinyl CoA synthetase, 6. Succinate dehydrogenase, 7. Fumarase, 8. Malate dehydrogenase.

Where does the final step of aerobic respiration occur and what is it called?

The electron transport chain occurs in the inner mitochondrial membrane of eukaryotes and in the plasma membrane of prokaryotes.

What is the product of the electron transport chain?

The product is water and a proton gradient that drives ATP synthesis via chemiosmosis.

What is the combined production of water and ATP via the electron transport chain called?

Oxidative phosphorylation.

What molecule acts as the final electron acceptor in aerobic cellular respiration?

Oxygen acts as the final electron acceptor and combines with two hydrogen ions to form water.

How many ATP are produced by the electron transport chain with oxidative phosphorylation?

Approximately 32 ATP molecules.

Name two molecules that help transport electrons in the electron transport chain.

Ubiquinone and Cytochrome C.

What is the difference between oxidative phosphorylation and substrate-level phosphorylation?

Substrate-level phosphorylation uses a substrate to phosphorylate ADP or GDP, while oxidative phosphorylation uses free energy from redox reactions in the electron transport chain to phosphorylate ADP to ATP.

What is glycolysis?

Glycolysis is a complex chemical pathway that occurs anaerobically in the cytoplasm of a cell.

Who was Joseph Priestly?

Priestly performed experiments emphasizing the importance of atmospheric gases in plant growth and is credited with the discovery of oxygen.

Who was Jan Ingenhousz?

He built on Priestley's work, hypothesizing that plants use sunlight to split carbon dioxide for growth and expel oxygen as a waste product.

Who discovered chloroplasts and their role in photosynthesis?

Julius von Sachs.

Who was Theodore Engelmann?

He was the first to describe the light-dependent reactions of photosynthesis.

Who was Melvin Calvin?

He traced the route of carbon throughout the entire process of photosynthesis.

What did James Clerk Maxwell illustrate?

He illustrated that the visible spectrum is a small portion of the electromagnetic spectrum.

Which end of the electromagnetic spectrum has more energy?

The smaller the wave, the higher the energy.

What absorbs light energy in living systems?

Pigments absorb light energy, with chlorophyll being the most important pigment in photosynthesis.

What are accessory pigments?

Accessory pigments are important pigments in plants that broaden the spectrum of visible light for photosynthesis.

What is the overall equation for photosynthesis?

6 CO2 + 6 H2O + light energy -> C6H12O6 + 6O2.

What are the two distinct metabolic pathways of photosynthesis?

Light Reactions (Light Dependent Reactions) and Light Independent Reactions.

Describe the light reactions of photosynthesis.

Chlorophyll a absorbs light energy, producing ATP, oxygen gas, and NADPH.

What is another name for the light independent reactions of photosynthesis?

Calvin Cycle, where carbon dioxide is incorporated into organic molecules.

Describe the structure of a typical leaf cross section.

A waxy cuticle covers the upper side, with an epidermis and stomata for gas exchange.

Where does most of the photosynthetic activity take place in the leaf?

In the cells of the palisade parenchyma.

What is the basic theory of paper chromatography?

It separates individual plant pigments using a stationary phase (paper) and a mobile phase (solvent).