Central Dogma and plasma membrane organisation and function Flashcards
Nucleus - function.
Central dogma basics. how does it work?
Structure?
DNA (transcription into)
is a base triplet - sequence of 3 nucleotides
double stranded
nucleus
RNA (translation into)
codon + anticodon
single stranded
nucleus and cytoplasm
Protein
amino acid
amino acid sequence determines the structure
anywhere in cell
DNA base triplet TRANSCRIPTION to RNA codon
definition of transcription
process by which genetic information encoded in DNA is spies onto a strand of RNA called messenger RNA (mRNA)
explain 3 process of transcription
initiation:
- RNA polymerase binding to START base triplet ATG
elongation;
RNAP reads a base triplet at a time and makes antisense RNA strand (mRNA)
DNA only unwrapped at site of transcription
termination;
RNAP stops transcribing when it reaches a STOP base triplet. (TAA, TAG, TGA)
RNA codon and anticodon to Protein amino acid
definition of translation
the process of reading the mRNA nucleotide sequence to determine the amino acid sequence of the protein
explain the 3 process of translation
initiation;
mRNA with a START codon first read by the ribosome with the antisense tRNA anticodon
that carries amino acid
elongation;
mRNA = template for ribosome to keep translating codons into anticodons on tRNA
which carries specific amino acid
process in ribosomes builds polypeptide chain becoming proteins
termination;
once ribosomes encounters STOP codon on mRNA
corresponding tRNA signals release of polypeptide chain from ribosome
plasma membrane
structure and function
S -
- flexible, sturdy barrier
- lipid bilayer
proteins. integral and peripheral membrane - fluid mosaic model
f -
- protect cell from the surroundings
- regulate movement of substances in and out of cell
- key role in communication among cells and between cells and external environment
lipid bilayer
structure
- phospholipids 75%
cholesterol 20%
glycolipids 5%
phospholipids
structure
- 75% of plasma membrane lips
2 parallel layers of molecules (BI/layer)
each molecule is amphipathic (BOTH polar and non polar region)
cholesterol
structure & function
S-
20% of cell membrane lips
- interspersed among other lipids in both layers
- OH group (polar)
- stiff steroid rings & hydrocarbon tail (non polar) and reside within fatty acid tails of phospholipids
Glycolipids
structure and function
comprise 5% of lipids of cell membrane
- carbohydrate group forms polar head
fatty acid tail are non polar
appear only in membrane that face ECF
f -
recognition from the outside
Membrane proteins
structure / s
classified according to whether they are firmly embedded in the membrane
integral proteins
- extend through lipid bilayer
- mostly transmembrane proteins (span entire bilayer)
- amphipathic
- firmly embedded
Peripheral proteins
- not as firmly embedded
- attached to polar head of membrane lips
- attached to integral proteins at inner or outer surface of membrane
functions of integral membrane proteins
ion channel carrier / transport protein receptor cell identity linker enzyme
functions of peripheral membrane proteins
cell identity
linker
enzyme
Functions of Integral protein Ion channel
allow specific ion t pass through water filled pore (Na+, K+, CI- channels)
functions of integral protein carrier / transporter
bind specific substance, change their shape and move it across membrane
(amino acid (glutamate) and glucose transporters)
functions of integral protein receptor protein
recognises specific extracellular ligand and alters cell’s function
(hormone receptors)
functions of integral and peripheral protein cell identity markers
allow for recognition of self
MHC proteins
functions of integral and peripheral protein linkers
anchors intracellular and extracellular filaments to the cell membrane and allow cell movement, cell shape and structure
(E-cadherin)
functions of integral and peripheral protein Enzymes
Catalyses reactions inside or outside the cell
lactase
what are the two Physical properties of plasma membrane
membrane fluidity
membrane permeability
membrane fluidity.
structure and function
S-
depends on number of double bonds in fatty acid tails of lipids (that make up bi layer)
and amount of cholesterol present
f-
- ensures free rotation / movement of proteins and lips within bilayer
- helps formation of cell junctions
- allows lipid bilayer to self seal if damaged
Membrane permeability
structure and function
S-
- lipid bilayer
- membrane proteins
- selectively self permeable (to small, non polar, uncharged molecules & water)
(impermeable to ions and charged (polar) molecules)
f-
ensures tight control of cellular homeostasis
- if cell adaption of concentration of intracellular ion levels is needed, its able to free movement of water across membrane and control transport of ion thus establishing gradients
what are the two gradients across membrane
concentration gradient
electrical gradient
what is the concentration gradient
the difference in concentration of molecule b/w two sides of plasma membrane
(oxygen & sodium ions are more concentrated outside cell with carbon dioxide. potassium ions more concentrated inside the cell)
What is electrical gradient
different in electrical charged across bilayer
(inner surface of plasma membrane is more negatively charged. outer surface is more positively charged. membrane potential)
what is the combined concentration and electrical gradients called?
electrochemical gradient
what are the 3 types of transport across plasma membrane?
Passive transport
active transport
vesicular transport
what are the 3 parts involved with passive transport?
simple diffusion
facilitated diffusion (channel and carrier)
osmosis
what are the two parts involved with active transport?
primary
secondary
what re the two types of vesicular transport?
endocytosis
exocytosis
definition of passive transport across plasma membrane
diffusion is the random mixing of particles (solute) that occurs in a solution (solvent) as result of kinetic energy of the particles.
what concentration do the molecules of solute / solution diffuse from?
high to low concentration
what influences diffusion rate across plasma membrane?
steepness of concentration gradient
temperature
size or mass of diffusing substance
surface area
diffusion distance
definition of passive transports simple diffusion
passive process where solute moves freely through lipid bilayer of plasma membrane of cell
without the help of membrane transport proteins.
(non polar, hydrophobic molecules (respiratory gases, some lipids, ammonia, fat soluble vitamins (A,D,E,K) and some small uncharged polar molecules (water, urea, small alcohols)
definition of passive transports facilitated diffusion.
how many types of facilitated diffusion is there?
spontaneous passive process of solute movement across biological membrane via specific transmembrane integral proteins
there are two types.
channel mediated
carrier mediated
(facilitated diffusion)
describe facilitated diffusion - channel mediated
a solute moves down its concentration gradient
across the lips bilayer
through a transmembrane protein acting as an ION channel
- allow passages of small, inorganic ions which ae hydrophilic (K+, Na+, Ca2+, CI-)
- ion channels are selective and specific on ion’s shape and charge leading to possibly gated (K+) or open all the time
describe facilitated diffusions - carried mediated
transmembrane protein acting a a carrier (transporter)
used to move solute down concentration gradient across plasma membrane
- molecule binds to carrier on one side of P.M
- causes carrier to undergo a change in shape
- so molecule can be released on other side
- solute binds more often on side of membrane with HIGHER concentration
- process depends on steepness of concentration gradient across membrane
explain facilitated diffusion of glucose
1 - glucose in ECF binds to specific carrier / transporter protein. (GluT) outside surface of membrane
2 - transporter undergoes change in shape. glucose passes through
3 - transporter release glucose into cytosol
definition of passive transport - osmosis
(Simple diffusion) net movement of solvent (water) through selectively permeable membrane from area of higher WATER concentration to area of lower water concentration.
OR from area of low SOLUTE concentration to area of high solute concentration
- only occurs when membrane is permeable to water but not certain solutes
- moves via simple diffusion
can move through aquaporins
(integral membrane proteins that function as water channels)
definition of tonicity. what are the three types of solutions
measure of solutions ability to change the volume of cells by altering their water concentration.
- isotonic
- hypotonic
- hypertonic
describe the three types of tonicity solutions
isotonic
- cell maintains shape and volume
- solute concentration same in solution and cell
hypotonic
- cell swells and bursts (lysis)
solute concentration lower in solution than in cell (inside force)
hypertonic
- cells shrink (crenation)
- solute concentration high in solution than in cell (outside force)
Active transport. Definition and why are the two types
energy requiring process that moves solutes via carrier proteins against a concentration gradient
- primary active
- secondary active
Describe primary active transport
energy derived from hydrolysis of ATP pumps substance across plasma membrane
against its concentration gradient
through a carrier protein
- maintain a low concentration of Na+ in cytosol
- maintain a high concentration of K+ in cytosol
- 3 Na+ expelled into ECF, 2 K+ imported into the cell
describe secondary active transport
energy stored in a Na+ or H+ concentration gradient drives OTHER substance against their own concentration gradient through carrier proteins (contras porter)
describe Antiporters and Symporters in relations to secondary active transport and allowing Na+ to leak back into cells
Antiporters
- carrier protein moves 2 substances in opposite direction
Symporters
- carrier protein moves 2 substances in same direction
describe Na+/glucose symporter
1 - primary active transport via Na+/K+ pump drives increase of Na+ outside cell
2 - Na+ travels down concentration gradient and enters cell via symporter
3 - Glucose enters the cell against concentration gradient via the same symporter
Describe Na+/Ca2+ antiporter
1 - primary active transport via Na+/K+ ATPase (3 Na+ out / 2 K+ in) drives increase of Na+ outside cell
2 - Na+ travels down concentration gradient and enter cell via anti porter
3 - Calcium exits cell against concentration gradient via same antiporter
