Cell Membranes and Nucleic Acids: Structure, Function, and Enzyme Kinetics

What is the primary function of cell membranes?

To serve as barriers, separating cellular contents from the external environment.

What is the composition of cell membranes?

Cell membranes are composed of a lipid bilayer formed by two layers of phospholipids.

What are the characteristics of the lipid bilayer in cell membranes?

The inner portion consists of nonpolar tails, while the outer portion features polar heads, making it amphiphilic.

What does amphiphilic mean in the context of cell membranes?

It means the lipid bilayer has both hydrophilic (water-attracting) and hydrophobic (water-repelling) properties.

What is selective permeability in cell membranes?

It allows the cell to control its internal environment by regulating what enters and exits.

List one essential function of biomembranes.

Acting as barriers to toxic molecules.

How do biomembranes facilitate nutrient transport?

They help in the transport and accumulation of nutrients necessary for cellular processes.

What role do biomembranes play in energy transduction?

They convert energy from one form to another.

What is the significance of lipid self-association in membrane formation?

It is driven by the hydrophobic effect, which minimizes the exposure of nonpolar tails to water.

What are monolayers and where do they form?

Monolayers form at the air-water interface, with lipid tails oriented away from water.

What are micelles?

Spherical structures where nonpolar tails are buried in the center, minimizing contact with water.

Describe the Fluid Mosaic Model of biomembranes.

It describes biological membranes as a fluid matrix where lipids and proteins can move laterally.

What are the two classes of membrane proteins in the Fluid Mosaic Model?

Peripheral (extrinsic) and integral (intrinsic) proteins.

What is the difference between peripheral and integral membrane proteins?

Peripheral proteins are loosely associated with the membrane, while integral proteins are embedded within the lipid bilayer.

What is passive diffusion?

The movement of uncharged species across a membrane based solely on concentration gradients.

What is facilitated diffusion?

A process involving transport proteins that increase the rate of diffusion for specific solutes.

What is the role of ligands in cell signaling?

Ligands interact with receptor proteins to initiate signaling and trigger signal transduction.

What are gated ion channels?

Membrane receptors that open in response to ligand binding, allowing specific ions to pass through the membrane.

What is the significance of membrane proteins in cell signaling?

They facilitate communication between cells and play crucial roles in signal transduction.

What influences the fluidity of the lipid bilayer?

Temperature and lipid composition.

What is the function of integral membrane proteins?

They often function in transport and signaling and are embedded within the lipid bilayer.

What is the importance of understanding membrane transport mechanisms?

It is essential for studying how cells interact with their environment and maintain homeostasis.

What is the role of membrane receptors in physiological processes?

They coordinate responses to external stimuli through cell signaling pathways.

What is the process of active transport?

A transport mechanism that requires energy to move substances against their concentration gradient.

What is the significance of the spontaneous formation of lipid bilayers?

It is a key characteristic of lipid behavior that stabilizes membrane structure.

How do integral proteins typically stabilize their structure?

They feature α-helices and β-sheets that stabilize their structure within the hydrophobic core.

What is the maximum transport rate in facilitated diffusion characterized by?

Saturation kinetics, where transport rates reach a maximum at high solute concentrations.

What is the function of potassium channels in facilitated diffusion?

They open and close in response to pH changes, facilitating the transport of potassium ions.

What are enzymatic receptors?

Receptors activated by ligands that often function as protein kinases, initiating signaling cascades.

What do GPCRs stand for?

G Protein-Coupled Receptors, which utilize G-proteins to transmit signals from receptors to downstream effectors.

What is the Fluid Mosaic Model?

A model describing the structure of cell membranes as a fluid combination of lipids and proteins.

What are peripheral proteins?

Proteins that are loosely attached to the membrane and can interact with the lipid headgroups.

What are integral proteins?

Proteins embedded within the membrane that can only be removed by disrupting the membrane.

What is active transport?

Movement of ions against a concentration gradient using energy, such as ATP.

What is a ligand?

A signaling molecule that binds to a receptor protein.

What is the primary structure of nucleic acids?

Nucleotides linked by 3' to 5' phosphodiester bonds, forming a sugar-phosphate backbone.

What are the two primary types of nucleic acids?

DNA (Deoxyribonucleic Acid) and RNA (Ribonucleic Acid).

What are the components of a nucleotide?

A nitrogenous base, a sugar, and a phosphate group.

What is the significance of Chargaff's rules?

They state that A pairs with T and G pairs with C, leading to complementary base pairing in DNA.

What is tautomerism in nitrogenous bases?

A chemical phenomenon where compounds exist in interconvertible forms, affecting base pairing and stability.

What is the role of restriction enzymes?

Proteins that cut DNA at specific sequences, crucial for genetic engineering.

What is the difference between nucleosides and nucleotides?

Nucleosides are formed when a nitrogenous base is linked to a sugar, while nucleotides have an additional phosphate group.

What is the sugar in RNA?

D-ribose.

What is the sugar in DNA?

2-deoxy-D-ribose.

What is the structure of DNA?

Typically double-stranded with a double helix structure featuring major and minor grooves.

Who provided critical insights into DNA structure through x-ray crystallography?

Rosalind Franklin.

What is the significance of the antiparallel nature of DNA strands?

It is crucial for the proper base pairing and stability of the DNA double helix.

What are membrane rafts?

Microdomains rich in cholesterol and sphingolipids within cell membranes.

What is the function of glycophorin?

A transmembrane protein found in human erythrocytes, characterized by its α-helical structure.

What is bacteriorhodopsin?

A seven-spanner integral protein involved in light-driven proton transport.

What are the two groups of nitrogenous bases?

Pyrimidines (C, U, T) and purines (A, G).

What is the direction in which the nucleotide sequence is read?

From 5' to 3'.

What are restriction enzymes?

Proteins that cleave DNA at specific sequences, crucial for genetic engineering and molecular biology techniques.

What is electrophoresis used for?

A technique used to separate DNA fragments based on size.

Define nucleic acids.

Linear polymers of nucleotides linked by phosphodiester bonds, including DNA and RNA.

What are nucleotides composed of?

A nitrogenous base, a sugar, and a phosphate group.

What is a phosphodiester bond?

A covalent bond that links the 3' carbon atom of one sugar molecule to the 5' carbon atom of another, forming the backbone of nucleic acids.

What are the two types of nitrogenous bases?

Pyrimidines (Cytosine, Uracil, Thymine) and Purines (Adenine, Guanine).

What is the structure of RNA?

Single-stranded, composed of ribonucleotides linked by phosphodiester bonds.

Who contributed to the understanding of DNA structure through x-ray crystallography?

Rosalind Franklin.

What do Chargaff's Rules state?

The amount of adenine equals thymine (A=T) and the amount of guanine equals cytosine (G=C).

What is the function of enzymes?

To act as protein catalysts that significantly accelerate biochemical reactions.

How do enzymes lower the activation energy?

By forming an enzyme-substrate (ES) complex at the active site, stabilizing the transition state.

What is enzyme kinetics?

The study of the rates of enzyme-catalyzed reactions and the factors affecting them.

What is the rate constant (k)?

A value that relates the rate of reaction to the concentrations of reactants, forming the basis of the rate law.

Define reaction order.

The dependence of the rate on the concentration of reactants, which can be zero, first, second, or higher order.

What is the active site of an enzyme?

A specific region within the enzyme that binds the substrate and facilitates the reaction.

What is the significance of coenzymes and cofactors?

Non-protein components that assist enzymes in their catalytic activity.

What is the typical yield of products from enzyme-catalyzed reactions?

Often exceeding 95%.

What is keto-enol tautomerism?

A chemical phenomenon where a compound exists in two interconvertible forms, affecting the structure of nucleobases.

What is the difference between DNA and RNA in terms of sugar?

DNA contains deoxyribose, while RNA contains ribose.

What are the naming conventions for nucleosides?

Purines end with 'osine', Pyrimidines end with 'idine', and DNA nucleosides start with 'deoxy'.

What is the role of enzymes in metabolic pathways?

They control the rates of essential biochemical processes in living organisms.

What is the molecularity of a reaction?

The number of reactant particles involved in a reaction, influencing the reaction mechanism.

What is the energy diagram in enzyme action?

It illustrates the difference in activation energy between uncatalyzed and catalyzed reactions.

How do enzymes achieve specificity?

Through the unique fit between the enzyme and its substrate.

What is the significance of studying enzyme kinetics?

It provides insights into enzyme mechanisms and metabolic pathways, which can be exploited for therapeutic purposes.

What forms when a substrate binds to the active site of an enzyme?

The enzyme-substrate (ES) complex.

What happens to the enzyme after it catalyzes a reaction?

The enzyme remains unchanged and can catalyze subsequent reactions.

What is the general reaction equation for enzyme-catalyzed reactions?

E + S ↔ ES → E + P, where E is the enzyme, S is the substrate, and P is the product.

What factors can influence the efficiency of enzymes?

Temperature, pH, and substrate concentration.

What is the transition state in enzyme kinetics?

A high-energy state that occurs during the conversion of substrates to products.

What is activation energy (ΔG‡)?

The energy required to reach the transition state, which enzymes help to lower.

How do enzymes affect activation energy?

Enzymes lower the activation energy, increasing reaction rates.

What does the Michaelis-Menten equation describe?

The rate of enzyme-catalyzed reactions as a function of substrate concentration.

What is Vmax in the context of enzyme kinetics?

The maximum reaction velocity of an enzyme-catalyzed reaction.

What does Km represent in enzyme kinetics?

The Michaelis constant, indicating the substrate concentration at which the reaction velocity is half of Vmax.

What is the significance of the saturation effect in enzyme kinetics?

At high substrate concentrations, the enzyme becomes fully utilized, limiting the reaction rate.

What is the purpose of measuring initial velocity (V0) in enzyme kinetics?

To gain insight into enzyme activity by measuring product formation over time at varying substrate concentrations.

What is the Lineweaver-Burk equation?

A linear representation of enzyme kinetics derived from the Michaelis-Menten equation.

What does the slope of the Lineweaver-Burk plot represent?

Km/Vmax.

What does a lower Km value indicate about an enzyme?

Higher substrate binding affinity and efficiency.

What is the turnover number (kcat)?

The number of substrate molecules converted to product per second.

What characterizes the active site of an enzyme?

A specific region where substrate binding occurs, influenced by the enzyme's structure.

What is enzyme specificity determined by?

The molecular architecture of the active site and its interactions with substrates.

What does the induced fit model describe?

How the active site undergoes conformational changes upon substrate binding.

What does the Lock and Key model suggest?

The enzyme's active site is complementary to the substrate, allowing for a precise fit.

How does temperature affect enzyme activity?

Enzyme activity generally increases with temperature up to an optimum point, beyond which denaturation occurs.

What is the optimum pH for enzymes?

The specific pH level at which an enzyme exhibits optimal activity.

How does substrate concentration influence reaction velocity?

Increasing substrate concentration typically increases reaction velocity until the enzyme becomes saturated.