cells and proteins

unit 1

allosteric enzymes

allosteric enzymes

Enzymes that change conformation in response to a modulator

alpha helix

Polypeptide chain coiled into a helix with hydrogen bonding occurring to maintain the arrangement

beta pleated sheet

Polypeptide chain arranged in rows with the chain folding in parallel or anti parallel arrangements

alternative RNA splicing

Removal of non coding introns from a primary mRNA transcript to leave only the coding exons; several different mature transcripts can be produced from a single primary transcript

Conformation

Structural arrangement of the polypeptide chains within a protein; it can be altered by factors such as pH and the binding of ligands and modulators

Co-operativity

Changes in binding of a target molecule to one subunit of a multi unit polypeptide changes the affinity of the other subunits for the target molecule

disulfide bridge

a strong covalent bond that stabilises the tertiary and quaternary structures of many proteins

endoplasmic reticulum

a network of membrane tubules within the cytoplasm of eukaryotic cell; continuous with nuclear membrane

exon

section of RNA that is usually retained during splicing

glycoprotein

a protein with a carbohydrate added by post translational modification

Golgi apparatus

a series of flattened membrane discs that packages proteins into membrane bound vesicles inside the cell before they are secreted from the cell membrane

hydrogen bond

attractions between polar molecules in which hydrogen is bound to a larger atom such as oxygen or nitrogen

hydrolases

a class of enzyme that can use water to break chemical bonds

intron

a section of RNA that is usually removed during splicing

ionic bonds

a type of chemical bonding which involves the electrostatic attraction between oppositely charged ions

ligand

a substance which can bind bind to a protein; the protein has a shape complimentary to the ligand to allow binding

London dispersion forces

a temporary weak attraction between atoms and molecules

lysosome

a modified golgi vesicle containing hydrolytic enzymes

modulators

these bind to a secondary site on an enzyme to alter its conformation; positive modulators activate enzymes and negative modulators deactivate enzymes.

monomers

a molecule that can bind chemically to other monomers to form polymers

non coding RNA genes

a gene that codes for RNAs other than mRNA, so do not code for a protein

phospholipid

component of cell membranes

polymer

a macromolecule composed of many repeated subunits (monomers)

post-translational modification

addition of chemical groups to, or modification of, a protein to allow a particular function

prosthetic group

a non-protein unit tightly bound to a protein and necessary for its function

protein kinase

catalyse the transfer of a phosphate group from a donor molecule (usually ATP) to an acceptor

protein phosphatases

an enzyme that removes a phosphate group from its substrate

primary structure

sequence in which amino acids are found within a protein

secondary structure

hydrogen bonding occurring within a polypeptide forming alpha helices or beta-pleated sheets

tertiary structure

bonding of many types occurring between R groups of amino acids within a protein

quaternary structure

the arrangement of multiple folded polypeptides connected together

proteolytic cleavage

a major form of post-translational modification; it occurs when a protease cleaves one or more bonds in a target protein to activate, inhibit or destroy the protein's activity

proteome

the entire set of proteins expressed by a genome; it is much larger than the genome

Rough Endoplasmic Reticulum

organelle made up of membranes with ribosomes attached

signal sequence

a short stretch of amino acids at one end of the polypeptide that determines the eventual location of a protein in a cell

Smooth Endoplasmic Reticulum

a membranous organelle found in most eukaryotic cells; its main functions are the synthesis of lipids and steroid hormones

turns

secondary structure that reverses the direction of a polypeptide chain

vesicles

small membrane bound compartments filled with liquid

electrochemical gradient

a gradient of electrochemical potential, usually for an ion that can move across a membrane, consisting of the difference in solute concentration and the difference in charge across a membrane

facilitated diffusion

the passive transport of substances across the membrane through specific transmembrane proteins

fluid mosaic model

a model that describes the structure of the plasma membrane as a mosaic of components including a phospholipid bilayer, which gives the membrane a fluid character, and cholesterol, proteins and carbohydrates

gated channels

channel forming proteins controlled by signalling molecules or ion concentration

Glucose symport

an integral membrane protein involved in transport of glucose and sodium ions across the cell membrane at the same time and in the same direction

integral membrane proteins

they have one or more segments that are embedded in the phospholipid bilayer

ligand gated channels

transmembrane protein channels controlled by the binding of signal molecules

membrane potential

an electrical gradient that forces ions to move passively in one direction; positive ions are attracted by the negative side of the membrane and negative ions by the positive one

peripheral membrane proteins

proteins that bind to the membrane without passing through it

sodium-potassium ATPase

the enzyme that acts as the sodium-potassium pump, removing three sodium ions from the cell and taking two potassium ions into the cell during a cycle of action

transmembrane proteins

Integral proteins that span the membrane and act as channels or transporters of ions

transporter proteins

a membrane protein involved in the movement of ions, small molecules, and macromolecules (such as another protein) across a membrane

voltage gated channels

a class of transmembrane proteins that form ion channels that are activated by changes in the electrical membrane potential near the channel

action potential

a wave of electrical excitation along a neuron's plasma membrane

cones

photoreceptor cells responsible for colour vision; they only function in bright light

cyclic GMP (cGMP)

a second messenger for visual transduction; it is present in high concentrations in photoreceptor cells

depolarisation

an electrical state in an excitable cell whereby the inside of the cell is made less negative relative to the outside than it is at the resting membrane potential

diabetes mellitus

an inability to regulate blood glucose levels; in type 1 there is a failure to produce insulin; in type 2 there is a loss of function in insulin receptors on a cell surface

extracellular signalling molecule

cues (such as growth factors, hormones, cytokines and neurotransmitters) designed to transmit specific information to target cells

GLUT 4 glucose transporter proteins

the insulin regulated glucose transporter; insulin triggers the movement of GLUT 4 transporters to the membrane surface, increasing uptake of glucose to be converted to glycogen

G-proteins

also known as guanine nucleotide-binding proteins, are a family of proteins that act as molecular switches inside cells, and are involved in transmitting signals from a variety of stimuli outside a cell to its interior

hormone response elements (HREs)

a short sequence of DNA within the promoter of a gene that is able to bind a specific hormone receptor complex and therefore regulate transcription.

Hormone Receptor Complex

formed when steroid hormones bind to specific receptors in the cytosol or the nucleus; they bind to specific sites on DNA and affect gene expression

hydrophilic

having a strong affinity for water

Hydrophobic

the tendency of non-polar substances to aggregate in aqueous solution and exclude water molecules; it is responsible for cell membrane and vesicle formation

hydrophilic signalling molecules

signalling molecules that are not able to pass through the membrane; the signal is transduced across the membrane by receptor molecules on the cell surface

hydrophobic signalling molecule

signalling molecules that can diffuse through membranes, so their receptor molecules can be within the nucleus

ion concentration gradient

gradients created by ion pump enzymes that transport ionic solutes, such as sodium, potassium, hydrogen ions and calcium, across the membrane; energy is required to produce a gradient, so the gradient is a form of stored energy

opsin

a light-sensitive protein molecule found in the animal kingdom

Phosphodiesterase (PDE)

enzyme that catalyses the hydrolysis of cyclic GMP (cGMP)

phosphorylation

the addition of a phosphate group to a molecule

phosphorylation cascade

a series of events in which one kinase activates the next one in a sequence phosphorylation cascades can result in the phosphorylation of many proteins as a result of the original signalling event

photon

the basic unit of light

photoreceptor cells

cells (rods and cones) found in the retina that are capable of visual phototransduction (converting light - visible electromagnetic radiation - into electrical signals)

repolarisation

restoration of a membrane potential following depolarisation (restoring a negative internal charge)

resting membrane potential

the difference in ion concentration between the inside and outside of a cell

retinal

a light sensitive molecule within the eye that binds with opsin to form photoreceptors in the eye

rhodopsin

the retinal-opsin complex in rod cells

rods

photoreceptor cells in the retina that function in dim light and respond to low light intensities; they do not allow colour vision

signal transduction

conversion of extracellular signals into an intracellular response

threshold value

when the depolarisation reaches about -55mV, a neuron will fire an action potential- this is the threshold; if the neuron does not reach this critical threshold level, the action potential will not fire

transcription factor

a protein that binds to specific DNA sequences, thereby controlling the rate of transcription of genetic information from DNA to messenger RNA.

transducin

A protein naturally expressed in vertebrate retina rods and cones and it is very important in vertebrate phototransduction (colour vision).

affinity

the degree to which a substance is attracted and tends to bind to another

affinity chromatography

a technique used to separate and purify proteins based on a specific binding interaction between an immobilised ligand and its binding partner

antigen

a specific protein with which antibodies can bind in an immune response

aseptic technique

procedures in place to prevent contamination, including sterilising equipment and work surfaces

bright-field microscopy

microscopy commonly used to observe whole organisms, parts of organisms, thin sections of dissected tissues or individual cells

buffer

a solution used to set and maintain a particular pH

centrifugation

a process which uses centrifugal forces to components of different densities in a mixture

colorimeter

a device used to measure the absorbance of a specific wavelength of light by a solution

culture media

a nutrient-rich culture media growth medium providing the basic requirements for cell growth

fluorescence microscopy

microscopy technique that uses specific fluorescent labels to bind to and visualise certain molecules or structures within cells or tissues

gel electrophoresis

technique used to separate samples of nucleic acid and protein by size; introduced to a gel, the move through it due to an electric current; smaller fragments move further than larger fragments

growth factors

proteins that promote cell growth and proliferation

inoculum

starting material used to grow a culture from, fro example a bacterial culture

serum

vitally important as a source of growth factors, hormones, lipids and minerals for the culture of cells

haemocytometer

microscopic grid used to estimate the total number of cells within a sample

hazard

anything that poses potential risk or threat to an individual or the environment

immunoassay

technique used to detect and identify specific proteins; antibodies linked with reporter enzymes

isoelectric point (IEP)

the pH at which a soluble protein has no net charge and will precipitate out of solution

linear dilution series

a series of dilutions that differ by an equal interval