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
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