1.2 proteins Flashcards
define proteome
the entire of of proteins that can be expressed by a genome
why the proteome is larger than the genome
more than one protein can be produced from a single gene as a result of alternative RNA splicing
alternative RNA splicing
one gene can produce different proteins as a result of which segments are treated as introns or exons
non-coding RNA genes
genes that don’t code for proteins
are transcribed to produce tRNA, rRNA or RNA molecules that control gene expression
factors that influence gene expression (4)
metabolic activity
cellular stress
signalling molecules
healthy vs diseased cells
internal membranes in eukaryotic cells
increase the total membrane surface area
allows for vital functions to be carried out
endoplasmic reticulum
forms a network of membrane tubules continuous with the nuclear membrane
smooth = lacks ribosomes
rough = ribosomes are docked on its cytosolic face
golgi apparatus
a series of flattened membrane discs
lysosomes
membrane-bound organelle containing digestive hydrolases
vesicles
transport materials between membrane compartments
synthesis of lipids
synthesised in smooth endoplasmic reticulum and are inserted into its membrane
synthesis of cytosolic proteins
synthesised in cytosolic ribosomes and remain in the cytosol
define signal sequence
a short stretch of amino acids that determines the eventual location of a protein in a cell
synthesis of transmembrane proteins
synthesis begins in cytosolic ribosomes
signal sequence directs ribosome to dock on endoplasmic reticulum (forms rough er)
translation continues
transmembrane protein is inserted into the er membrane
movement of vesicles
vesicles containing proteins bud of from er
fusion with golgi apparatus
bud off from one golgi disc and fuse with the next in the stack
post-translational modifications
proteins undergo as they move through golgi apparatus
addition of carbohydrates to form glycoproteins
vesicles that leave golgi apparatus
take proteins to plasma membrane and lysosomes
move along microtubules to other membranes and fuse with them
synthesis of secreted proteins
translated in ribosomes on rough er and enter its lumen
secretory pathway
proteins move through golgi apparatus and are packaged into secretory vesicles
fusion with plasma membrane and are released out of the cell
proteolytic cleavage
a type of post-translational modification
can produce active proteins from inactive precursors
amino acids
amine group and carboxyl group
formed by condensation reactions
linked by peptide bonds
purpose of R groups
determine the protein’s position in the cell and overall conformation
acidic R group
second carboxyl group
negatively charged
form ionic bonds
hydrophilic
basic R group
second amine group
positively charged
form ionic bonds
hydrophilic
polar R group
hydroxyl group
overall neutral
form hydrogen bonds
hydrophilic
non-polar R group
attracts only other non-polar R groups
hydrophobic
factors affecting R groups
temperature and pH disrupt interactions between R groups
primary structure
sequence of amino acids along a polypeptide chain
secondary structure
form due to hydrogen bonds
alpha helix, beta-pleated sheets, beta turns
tertiary structure
form due to interactions between R groups
London dispersion forces, hydrophobic interactions, ionic bonds, hydrogen bonds, disulphide bridges
quaternary structure
occurs in proteins with multiple polypeptide subunits
linked by interactions between R groups of adjacent subunits
prosthetic groups
non-protein units tightly bound to a protein
essential for the protein’s function
define ligand
non-protein substance which binds to a protein and alters its conformation and function
allosteric interactions
occur between spatially distinct sites
ligand binding on one site increases affinity of other sites
co-operativity
shown in allosteric proteins of quaternary structure
changes at one subunit alters the affinity at remaining subunits
factors affecting oxygen affinity in haemoglobin
decrease in pH/ increase in temperature lowers oxygen affinity, so more oxygen is released
allosteric enzymes
have secondary allosteric sites for modulator binding
types of modulators
positive = increase affinity
negative = decrease affinity
protein kinase
catalyse the phosphorylation of proteins
protein phosphatase
catalyse the dephosphorylation of proteins
