Cell Membrane and Transport Mechanisms

These flashcards cover key concepts related to cell membrane structure, transport mechanisms, and proteins.

Enzymes

Biological catalysts that speed up chemical reactions without being consumed.

Hydrogen Bonds

More like a magnetic attraction than a real bond, occurring between an electronegative atom and a nearby hydrogen atom.

G protein receptor mechanism

A signaling pathway involving binding of a ligand that activates a G protein, leading to a signal transduction pathway within the cells.

Protein Formation

Proteins are formed through peptide bonds between amino acids; their three-dimensional structure is determined by the sequence of amino acids.

Osmolarity

Total concentration of solute particles in a solution, equivalent to molar concentration.

Passive Membrane Transport

The passage of water and solutes through a membrane without atp or proteins

Active Transport

The movement of solutes across a membrane using ATP, requiring carrier proteins.

Tonicity

How a solution affects cell volume, categorized as isotonic, hypertonic, or hypotonic.

Fluid Mosaic Model

A model describing cellular membrane structure as a mosaic of phospholipids and proteins.

Osmosis

The diffusion of water across a semipermeable membrane.

Sodium Potassium Pump

A primary active transport mechanism that moves sodium and potassium ions across the cell membrane.

Endocytosis

The process of taking substances into a cell by engulfing them in a vesicle.

Exocytosis

The process of releasing substances from a cell by vesicular transport.

Enzymes

Biological catalysts that speed up chemical reactions without being consumed.

Enzyme Active Site

The region on an enzyme where substrate molecules bind and undergo a chemical reaction.

Enzyme Specificity

The ability of an enzyme to catalyze only one type of reaction or react with only one type of substrate.

Factors Affecting Enzyme Activity

Temperature, pH, substrate concentration, and the presence of inhibitors or activators.

Hydrogen Bonds

More like a magnetic attraction than a real bond, occurring between an electronegative atom and a nearby hydrogen atom.

Role of Hydrogen Bonds in Water

Responsible for water's high surface tension, specific heat capacity, and its ability to act as a universal solvent.

Hydrogen Bonds in Macromolecules

Critical for maintaining the secondary ( \alpha - ext{helices}, \beta - ext{sheets}) and tertiary structures of proteins, and the double helix structure of DNA.

G protein receptor mechanism

A signaling pathway involving binding of a ligand that activates a G protein, leading to a signal transduction pathway within the cells.

G Protein-Coupled Receptors (GPCRs)

A large family of cell surface receptors that respond to a variety of extracellular stimuli by activating internal G proteins.

G Protein Components

Composed of alpha ( \alpha ), beta ( \beta ), and gamma ( \gamma ) subunits; the alpha subunit binds GDP/GTP.

Second Messengers

Intracellular molecules (e.g., cAMP, IP3, DAG, ext{Ca}^{2+} ) that relay signals from receptors to target molecules within the cell.

Protein Formation

Proteins are formed through peptide bonds between amino acids; their three-dimensional structure is determined by the sequence of amino acids.

Peptide Bond

A covalent bond formed between the carboxyl group of one amino acid and the amino group of another, with the release of a water molecule.

Primary Protein Structure

The unique linear sequence of amino acids linked by peptide bonds.

Secondary Protein Structure

Local folding of the polypeptide chain into alpha ( \alpha )-helices or beta ( \beta )-sheets, stabilized by hydrogen bonds.

Tertiary Protein Structure

The overall three-dimensional shape of a single polypeptide chain, resulting from interactions between amino acid side chains.

Quaternary Protein Structure

The arrangement of multiple polypeptide subunits in a functional protein complex.

Osmolarity

Total concentration of solute particles in a solution, equivalent to molar concentration.

Effective Osmolarity

The concentration of osmotically active particles that cannot cross the cell membrane, determining water movement.

Passive Membrane Transport

The passage of water and solutes through a membrane, influenced by hydrostatic pressure and pressure gradients.

Diffusion

The net movement of solutes from an area of higher concentration to an area of lower concentration, down their concentration gradient.

Facilitated Diffusion

The passive movement of molecules across the cell membrane via specific transmembrane integral proteins (channels or carriers) without ATP.

Channel Proteins

Transmembrane proteins that form pores allowing specific ions or small molecules to pass through the membrane by facilitated diffusion.

Carrier Proteins

Transmembrane proteins that bind to specific molecules and undergo a conformational change to transport them across the membrane by facilitated diffusion.

Active Transport

The movement of solutes across a membrane using ATP, requiring carrier proteins.

Primary Active Transport

Directly uses ATP to move solutes against their concentration gradient, often involving pumps (e.g., Na/K pump).

Secondary Active Transport

Uses the energy stored in an electrochemical gradient (created by primary active transport) to move a second solute against its concentration gradient.

Cotransport (Symport)

A type of secondary active transport where two different solutes move in the same direction across the membrane.

Countertransport (Antiport)

A type of secondary active transport where two different solutes move in opposite directions across the membrane.

Tonicity

How a solution affects cell volume, categorized as isotonic, hypertonic, or hypotonic.

Isotonic Solution

A solution with the same solute concentration as the cell cytoplasm, causing no net water movement and no change in cell volume.

Hypertonic Solution

A solution with a higher solute concentration than the cell cytoplasm, causing water to leave the cell and the cell to shrink (crenation).

Hypotonic Solution

A solution with a lower solute concentration than the cell cytoplasm, causing water to enter the cell and the cell to swell, potentially bursting (lysis).

Fluid Mosaic Model

A model describing cellular membrane structure as a mosaic of phospholipids and proteins.

Phospholipid Bilayer

The basic structure of the cell membrane, consisting of two layers of phospholipids with hydrophilic heads facing outwards and hydrophobic tails facing inwards.

Amphipathic Phospholipids

Molecules containing both hydrophilic (water-loving) and hydrophobic (water-fearing) regions, characteristic of phospholipids.

Membrane Proteins

Integral proteins are embedded within the lipid bilayer, while peripheral proteins are loosely attached to the surface.

Osmosis

The diffusion of water across a semipermeable membrane.

Osmotic Pressure

The pressure that must be applied to a solution to prevent the net flow of water across a semipermeable membrane due to osmosis.

Aquaporins

Specific channel proteins that facilitate the rapid movement of water across cell membranes.

Sodium Potassium Pump

A primary active transport mechanism that moves sodium and potassium ions across the cell membrane.

Na/K Pump Ion Movement

Pumps 3 ext{Na}^+ ions out of the cell and 2 ext{K}^+ ions into the cell for each ATP molecule hydrolyzed, maintaining membrane potential.

Electrogenic Pump

A pump (like the Na/K pump) that generates an electrical current across the membrane by moving a net charge (e.g., 1 positive charge out per cycle).

Endocytosis

The process of taking substances into a cell by engulfing them in a vesicle.

Phagocytosis

A type of endocytosis where the cell engulfs large particles or whole cells (cell eating).

Pinocytosis

A type of endocytosis where the cell ingests extracellular fluid and its dissolved solutes (cell drinking).

Receptor-Mediated Endocytosis

A highly specific type of endocytosis where target molecules bind to specific receptors on the cell surface before being engulfed.

Exocytosis

The process of releasing substances from a cell by vesicular transport.

Constitutive Exocytosis

A continuous process of vesicle fusion with the plasma membrane, releasing substances for extracellular matrix formation or membrane renewal.

Regulated Exocytosis

Exocytosis that occurs only in response to a specific signal, such as the release of neurotransmitters or hormones.

What is Mitosis?

The process of nuclear division in eukaryotic cells that results in two daughter cells each having the same number and kind of chromosomes as the parent nucleus.

Phases of Mitosis

Mitosis is divided into four main phases: Prophase, Metaphase, Anaphase, and Telophase, followed by Cytokinesis.

Prophase

Chromatin condenses into visible chromosomes, the nuclear envelope breaks down, and the spindle fibers begin to form from the centrosomes.

Metaphase

Chromosomes align at the metaphase plate (equatorial plate) in the center of the cell, with each chromatid attached to a spindle fiber from opposite poles.

Anaphase

Sister chromatids separate and move towards opposite poles of the cell, becoming individual chromosomes, as the spindle fibers shorten.

Telophase

Chromosomes arrive at opposite poles and begin to decondense, the nuclear envelope reforms around each set of chromosomes, and the spindle fibers disappear.

Cytokinesis

The division of the cytoplasm follows nuclear division, resulting in two separate daughter cells, each with its own nucleus and complete set of organelles.