Cell Biology Combined Quest 2

What are the seven major functions of membranes?

The seven major functions are compartmentalization, selective permeability, communication and signaling, energy transformation, transport, enzymatic activity, and cell recognition.

Describe the experiment that first revealed that the plasma membrane was a lipid bilayer.

The experiment involved electron microscopy to visualize the structure of membranes and differential centrifugation to separate cellular components, leading to the conclusion of a lipid bilayer.

What is the fluid-mosaic model?

The fluid-mosaic model describes the plasma membrane as a dynamic structure with various proteins embedded in or associated with a fluid lipid bilayer.

What are the primary components of membranes?

The primary components are phospholipids, cholesterol, and proteins, which vary among different cell types and organelles.

What does amphipathic mean?

Amphipathic refers to molecules that have both hydrophilic (water-attracting) and hydrophobic (water-repelling) parts.

Name and describe the three main types of membrane lipids.

The three main types are phospholipids (form bilayers), cholesterol (stabilizes membrane fluidity), and glycolipids (involved in cell recognition and signaling).

What is a liposome?

A liposome is a spherical vesicle composed of a lipid bilayer, used to deliver drugs or genetic material.

What is a stealth liposome?

A stealth liposome is a liposome designed to evade the immune system for targeted drug delivery.

Why is it important that membranes are fluid?

Fluidity allows for proper function, including protein mobility, cell signaling, and membrane fusion.

Why are the inner and outer membrane leaflets different?

They are different because of the asymmetric distribution of lipids and proteins important for various cellular functions.

How is ABO blood typing related to the membrane?

ABO blood typing is determined by the presence of specific glycoproteins on the surface of red blood cell membranes, defining blood types.

Describe the three classes of membrane proteins.

Integral proteins (span the membrane), peripheral proteins (associated with the membrane surface), and lipid-anchored proteins (attached to lipids in the membrane).

What does Freeze-fracture analysis show?

It shows the architecture of the plasma membrane, revealing the distribution of proteins and lipids.

How would you solubilize an integral membrane protein?

Use detergents or organic solvents to disrupt the lipid bilayer and isolate the protein.

What types of amino acids are typically found in transmembrane domains?

Hydrophobic amino acids are typically found in transmembrane domains to interact with the lipid bilayer.

What is a hydropathy plot?

A hydropathy plot is a graphical representation used to predict transmembrane regions of proteins based on amino acid hydrophobicity.

Describe how to use site-directed mutagenesis to identify relationships between proteins.

By introducing specific mutations and analyzing the effects on protein function, researchers can determine spatial and functional relationships.

What factors influence membrane fluidity?

Factors include temperature, lipid composition (saturation level), and cholesterol content.

What are lipid rafts?

Lipid rafts are microdomains within membranes enriched in cholesterol and sphingolipids, believed to organize signaling molecules.

Describe an experiment showing dynamic protein nature in the plasma membrane.

FRAP (Fluorescence Recovery After Photobleaching) experiments show how proteins move within the membrane over time.

Why do proteins move more rapidly in artificial membranes versus real cellular membranes?

In artificial membranes, the lack of complex cellular structures and interactions allows for greater protein mobility.

What are the four mechanisms by which solute molecules move across the membrane?

Diffusion, facilitated diffusion, active transport, and vesicular transport.

What is the difference between diffusion and active transport?

Diffusion is passive movement down a concentration gradient, while active transport requires energy to move solutes against their concentration gradient.

What is the partition coefficient?

The partition coefficient measures the solubility of a substance in a lipid phase versus an aqueous phase, indicating membrane permeability.

What is osmosis?

Osmosis is the movement of water through a semi-permeable membrane from an area of lower solute concentration to an area of higher solute concentration.

What happens to a cell in hypotonic, hypertonic, and isotonic solutions?

In hypotonic solutions, cells swell due to water intake. In hypertonic solutions, cells shrink due to water loss. In isotonic solutions, cells remain stable.

When might a plant cell undergo plasmolysis?

Plasmolysis occurs when a plant cell is placed in a hypertonic solution, causing the cell membrane to pull away from the cell wall.

What are aquaporins?

Aquaporins are channel proteins that facilitate the rapid transport of water across cell membranes.

What is turgor pressure?

Turgor pressure is the pressure exerted by the fluid inside the central vacuole of plant cells against the cell wall.

What is the permeability of membranes for ions, water, macromolecules, and small uncharged molecules?

Membranes are generally impermeable to ions and macromolecules, but permeable to water and small uncharged molecules to some extent.

What are some properties of ion channels?

Ion channels are selective, gated, and may be voltage- or ligand-gated, allowing ions to pass through when open.

What do patch clamping experiments show?

Patch clamping demonstrates the ionic currents flowing through individual ion channels and their dynamics.

What does it mean that most ion channels are gated?

Gated ion channels open or close in response to specific stimuli like voltage changes or ligand binding.

What are the three types of ion channels?

Voltage-gated, ligand-gated, and mechanically-gated ion channels.

Describe how the voltage-gated potassium channel works.

It opens in response to membrane depolarization, allowing K+ ions to flow out, repolarizing the membrane.

Describe facilitated diffusion with the glucose transporter.

Facilitated diffusion involves a glucose transporter that binds glucose and changes conformation to allow its passage into the cell.

Describe active transport using the Na+/K+ ATPase.

The Na+/K+ ATPase pump actively transports Na+ out of and K+ into the cell, using ATP to maintain gradients.

What is a P type pump? Name an example.

A P type pump is an ATPase that adds a phosphate group to itself; an example is the Na+/K+ ATPase.

What is a V type pump?

V type pumps are ATPases that transport protons across membranes, such as those found in organelles.

What is an ATP-binding cassette protein?

ATP-binding cassette (ABC) proteins are a family of transporters that utilize ATP to transport various substrates across membranes.

What is a membrane potential?

Membrane potential is the voltage difference across a membrane due to the distribution of ions.

What is a resting potential?

Resting potential is the electrical charge difference across the plasma membrane of a neuron at rest.

What types of cells have a resting potential?

Neurons, muscle cells, and other excitable cells have resting potentials.

What is a neuron?

A neuron is a specialized cell that transmits nerve impulses.

Name the parts of a typical neuron and their functions.

Dendrites (receive signals), cell body (process signals), axon (conduct signals), and axon terminals (transmit signals to other cells).

How are K+ gradients across the membrane maintained?

K+ gradients are maintained by the Na+/K+ ATPase pump and selective permeability of the membrane.

Which ions are typically more concentrated inside versus outside the cell?

K+ is more concentrated inside, while Na+, Cl-, and Ca++ are more concentrated outside.

How is an action potential generated?

An action potential is generated when depolarization reaches a threshold, leading to rapid influx of Na+.

What does it mean that excitable membranes exhibit all-or-none behavior?

It means once the threshold is reached, an action potential is generated fully, or not at all.

What two criteria primarily affect the speed of a nerve impulse?

Axon diameter and myelination influence the speed of nerve impulse conduction.

Describe impulse propagation for non-myelinated and myelinated neurons.

In non-myelinated neurons, impulses propagate continuously; in myelinated neurons, impulses jump between nodes of Ranvier, speeding transmission.

What is a synapse?

A synapse is a junction where nerve signals are transmitted between neurons or from neurons to other cells.

Describe the importance of neurotransmitters.

Neurotransmitters are chemical messengers that transmit signals across synapses, facilitating communication between neurons.

How is neurotransmitter action terminated?

Neurotransmitter action is terminated by reuptake, enzymatic degradation, or diffusion away from the synaptic cleft.

Describe impulse transmission with acetylcholine as the neurotransmitter.

Acetylcholine is released from the presynaptic neuron, binds to receptors on the postsynaptic neuron, triggering impulse transmission.

How do different cone snail toxins affect impulse transmission?

Cone snail toxins can block ion channels or interfere with neurotransmitter release, affecting nerve impulse transmission.

Bioenergetics

The study of the various types of energy transformations that occur in living organisms

Energy

capacity to do work, or the capacity to change or move something

Thermodynamics

the study of the changes in energy that accompany events in the universe

First Law of Thermodynamics

The law of conservation of energy states that energy can neither be created nor destroyed. Cells are capable of energy transduction. The universe can be divided into systems and surroundings.

Second Law of Thermodynamics

events in the universe tend to proceed from a state of higher energy to a state of lower energy (spontaneous events). Every event is accompanied by an increase in the entropy of the universe

Transduction

conversion of energy from one form to another

Examples of energy transduction

electric energy can be transduced to mechanical energy when we plug a clock in. Chemical energy is converted to mechanical energy when heat is released during muscle contraction. Animals, such as fireflies and luminous fish, are able to convert chemical energy back to light

Where is chemical energy stored?

In certain biological molecules like ATP

photosynthesis

conversion of sunlight into chemical energy

What is a system?

a subset of the universe under study

What are the surroundings in a system?

everything that is not a part of a systemthat interacts with the system.

internal energy

energy of the system. change in Eis related to heat and work.

Exothermic reactions

reactions that lose heat

Endothermic

reactions that gain heat

First law of thermodynamics equation

change in E = Q - W, where E is internal energy, Q is heat energy, and W is the work energy

Spontaneous events

events that occur without the input of external energy (second law of thermodynamics)

Entropy

measure of randomness or disorder. associated with random movements of particles or matter

First and Second Law combined equation

change in H = change in G + T change in S, where free energy is change in G, enthlapy is change in H, change in s is change in entropy. change in g is spontaneity of the reaction. <0 reaction is exergonic, >0 it is endergonic

Enzymes

catalysts that speed up chemical reactions. almost always proteins. Can be conjugated with non-protein components

Cofactors

inorganic enzyme conjugates

Coenzymes

organic enzyme conjugates

Properties of enzymes

Present in small amounts, not permanently altered during course of reaction, can’t affect thermodynamics of reactions (only rates), highly specific for their particular reactants called substrates, produce only appropriate metabolic products, and can be regulated to meet needs of cell

Activation Energy

small energy input that is required for any chemical transformation. It slows the progress of thermodynamically unstable reactants

transition state

reactant molecules that reach the peak of the EA barrier

What happens without an enzyme?

only a few substrate molecules reach transition state

What happens when there is a catalyst?

a large proportion of substrate molecules can reach the transition state

Enzyme-substrate complex

when an enzyme interacts with its substrate if forms this (active sites)

active sites

substrate that binds to a portion of the enzyme. have complementary shapes with substrates that allow substrate specificity

What is the formation of an enzyme-substrate complex?

pyruvate kinase, PEP, and ATP

induced fit

shifts in the conformation after binding.

How have researchers determined the three dimension structure of an enzyme at successive stages during a reaction?

By using time-resolved crystallography

3 ways enzymes accelerate reactions

substrate orientation, changing substrate reactivity, and inducing strain in the substrate

How can Enzymes accelerate reactions through substrate orientation?

multiple substrates brought together in correct orientation to catalyze reactions. Changes in atomic and electronic structure occur in both enzyme and substrate during reaction.

How can enzymes accelerate reactions through changing substrate reactivity?

Substrate influenced by amino acid side chains at active site that alter chemical properties (e.g. charge) of substrate. This temporarily stabilizes the transition site.

How do enzymes accelerate reactions by inducing strain in the substrate?

enzyme changes conformation of substrate to being closer to conformation of transition state. Shifts in the conformation after binding cause an induced fit between enzyme and substrate. Covalent bonds are strained

Examples of ways enzymes accelerate reactions through changing substrate reactivity

Acidic or basic R groups on the enzyme may change the charge of substrate. Charged R groups may attract substrate. Cofactors of enzyme increase the reactivity of substrate by removing or donating electrons

Kinetics

Study of rates of enzymatic reactions under various experimental conditions. These rates can increase with increasing substrate concentrations until the enzyme is saturated

What happens when an enzyme is saturated?

Every enzyme is working at maximum capacity

Maximal velocity or Vmax

velocity at saturation

turnover number

number of substrate molecules converted to product per minute per enzyme molecule at Vmax

Michaelis Constant (KM)

substrate concentration at one-half of Vmax. Units of KM are concentration units. The KM may reflect the affinity of the enzyme for the substrate.

What do Lineweaver-Burk plots show?

plots of the inverses of velocity versus substrate concentrations. facilitate estimating Vmax and KM

Enzyme inhibitors

slow the rates for enzymatic reactions

irreversible enzyme inhibitors

bind tightly to the enzyme