Cell Physiology Flashcards
What is the plasma (cell) membrane?
Surrounds the cell surface
- separating the intercellular fluid from extracellular environment/extracellular fluid
What are cell organelles?
- Perform specific functions and compartmentalize the cell
- can be membrane bound and non-membrane bound
What are the main components of the cell?
- nucleus
- cytoplasm (region outside the nucleus) that contains organelles and cytosol (gel-like fluid)
What are the functions of the plasma (cell) membrane?
- physical barrier
- keeps organelles and proteins inside cell
- maintains difference in fluid composition between ECF/ICF (maintains ionic composition)
- maintains homeostasis
- cell-to-cell communication
- contains receptors that bind specific signalling molecules arriving at the cell surface
- structural support
- specialized connections between plasma membrane or between membranes and extracellular materials
- transport (in and out of cell)
- selectively permeable
True or False: All biological membranes are made the same
False: Biological membranes are not all made the same
- each can have a different ratio of lipid and proteins
- each ratio reflects a different function of the cell or organelle
What are lipids?
- primarily made of carbon and hydrogen (linked by non-polar / neutral covalent bonds)
- most contain oxygen and some contain phosphates (may provide polarity depending on structure)
What are the 3 main types of membrane lipids?
- phospholipids
- cholesterol
- glycolipids
What are the key characteristics of phospholipid structure?
- amphipathic (polar head group and non-polar tail)
- polar head group = hydrophilic
> phosphate attached to glycerol
> nitrogen-containing chemical group (R)
> glycerol backbone - non-polar tail = hydrophobic
> 2 fatty acid chains (carbon and hydrogen)
> saturated (single bond)
> unsaturated (double bond) - spontaneously form bilayer
What is an important steroid lipid found in cell membranes? And what is its structure? And what is its function?
1) Cholesterol
2) Structure:
- contains 3 six carbon rings
- 1 five carbon ring
- C-H chemical group attached to one of the rings (non polar)
- single polar hydroxyl group
3) Function:
- amphipathic
- prevents fatty acid chain from packing together and crystallizing to maintain membrane fluidity
What are glycolipids?
- lipids with CHO chain attached
- outer leaflet of plasma membrane
- amphipathic (polar and non-polar regions)
- form glycocalyx
What is the glycocalyx?
- layer of carbohydrates linked to lipids
- helps cell with identification and interaction between cells
What are the three main types of membrane proteins?
1) Integral:
- amphipathic
- transmembrane proteins (exposed to cytosol and extracellular fluid, can span bilayer once or more than once)
2) Peripheral:
- not amphipathic
- inner/outer surface of membrane (most on cytosolic side)
3) Glycoproteins
- protein with attached carbohydrates
- located on extracellular surface of plasma membrane (also help form glycocalx)
True or False: All proteins are distributed unequally in the cell membrane.
True: Asymmetry is related to the function of a cell
what is considered the smallest cell of the body and why is it small
the red blood cell and it helps with surface area
what is cytosol made of
proteins, electrolytes and water
what are the most abundant type of membrane lipids
phospholipids
true or false - glycoproteins form glycocalyx
true
what are the three types of desomosomes
cadherins, plaques and intermediate filaments
_____ are cell junctions that are found in areas that are exposed to a lot of tension and stretching
desmosomes
_____ are a type of desmosome that links cells together
cadherins
where can tight junctions be found
in epithelial cells and intestines
what is an example of a tight junction and what is their importance
occludins; limit movement of structures inside and outside the cell as well as form impermeable junctions
what is the importance of gap junctions
they are transmembrane channels that directly connect the cytoplasms of two cells
where are gap junctions found
mainly the heart, cardiac muscle
what is the largest organelle in the body
nucleus
what are the two organelles that have double layered porous membrane
mitochondria and nucleus
where does the synthesis of ribosomal RNA occur
nucleolus
true or false - skeletal muscle cell has no nucleus
false - it is multinucleate
what are ribosomes responsible for
protein synthesis
what are the two types of ribosomes and where are they found
free - in cytoplasm
bound - ER
what is the difference between rough and smooth ER
rough ER has ribosomes attached to its surface whereas smooth ER does not
pick the odd one out and replace it with the right answer
the smooth ER has these three functions
- stores calcium, synthesizes proteins and detoxifies drugs
it does not synthesize proteins, it synthesizes lipids - only the rough ER synthesizes proteins
what is the name of the curved membrane bound sacs in the Golgi apparatus
cisternae
true or false - lysosomes do not function at an acidic pH
false - they do
what are the two functions of lysosomes
- breakdown macromolecules into their subunits using hydrolytic enzymes
- destroy debris such as viruses and bacteria
what structure provides the mitochondria with a lot of surface area
cristae
true or false - mitochondria have their own DNA
true
what are examples of structures with lots of mitochondria
skeletal and heart muscle, sperm
what are the three ways of endocytosis
phagocytosis, pinocytosis and receptor-mediated endocytosis
what kind of substances does pinocytosis take up
small molecules, ions and nutrients
put the steps of phagocytosis in order
pseudopodia, attachment, destruction, formation of phagolysosome, recognition, release
recognition, attchment, psudopodia, formation of phagolysosome, destruction then release
what is the name of the vesicle formed from receptor-mediated endocytosis and what are its three functions
clathrin-coated vesicle
1. deposit contents into lumen
2. fuse with plasma membrane to release contents
3. fuse with endosomes so that the contents can be sorted to where they need to go
if phagocytosis is not able to digest the substance , what happens
exocytosis
what are the functions of exocytosis
- secrete specific substances
- release waste
- replace the portions of plasma membrane that were removed by endocytosis
pick the odd one out and replace it with the correct answer
- chemical
- mechanical
- electrochemical
mechanical -> electrical
what drives a chemical driving force
concentration gradient with different concentrations on other side
true or false - molecules flow from high to low concentration
true
how does the electrical driving force work
ion experiences attractive or repulsive forces due to the membrane potential
what does the direction of the electrochemical driving force depend on
on the net direction of electrical and chemical driving forces
what are examples of molecules that can pass through simple diffusion
co2, O2, fatty acids and ethanol
what is the most favorable characteristics of molecules that can pass through simple diffusion
non polar, uncharged and small
true or false - ions can pass through simple diffusion
false - they have a charge
direction of simple diffusion flow
high to low concentration
what are the three factors influencing the rate of simple diffusion
magnitude of driving force, surface area and membrane permeability
true or false - the smaller the surface area, the greater the rate of simple diffusion
false - *the greater the surface area
how does the diffusing distance affect the rate of simple diffusion
the rate of diffusion is inversely proportional to distance
true or false - the higher the temperature the greater the rate of diffusion
true
briefly explain passive transport
it is a type of mediated transport where molecules move through carriers or channels, down a concentration gradient with a help of a protein
are mediated transporters specific or non specific
specific
what is the direction of net flux for carrier mediated diffusion
high to low concentration
what determines the ion flux in channel mediated diffusion
electrochemical gradient
what are the three types of gates involved in channel mediated facilitated diffusion
voltage, ligand and mechanical
other than passive transport, what is another example of mediated transport
active transport
true or false - active transport does not require energy
false - it does, for example ATP
active transport moves ____ its concentration gradient and from ____ to ____ concentration
down/against ; high/low
against ; low to high
in primary active transport, what is the net charge as calcium and potassium are being transported
+1
3 ___ out, 2 ___ in per ATP that is hydrolyzed
Na+, K+
what are the concentrations of the sodium and potassium once the gradient has been created
high Na outside and high K inside
what is the name of the enzyme that helps create the concentration gradient in primary active transport
Na/K ATPase
what is the energy source of secondary active transport
the electrochemical gradient
how does the process of secondary active transport work
as one ion moves down its electrochemical gradient, it couples the movement of another molecule to move against the gradient
what is the name for two substances transported in the same direction
cotransport/symport
what is an example of an antiport
Na/H exchanger
what is an example of a symport
Na/glucose cotransporter
match the term to the transporter
electrogenic and electroneutral
symport and antiport
electrogenic and symport
antiport and electroneutral
what does it mean when a transport is saturable
mediated transport is saturable because there a finite/limited number of binding sites and protein transporters
true or false - simple diffusion is non saturable
true because it does not need to compete for protein transporters and there is no limitation
what are the two types intercellular communication
direct and indirect
what is an example of direct intercellular communication
gap junctions
what is an example of indirect intercellular communications
lipid soluble or insoluble chemical messengers
what are transcription factors
alters transcription of mRNA by binding to a specific sequence of DNA at the beginning of the gene
what is the term used for the specific sequence of DNA near the beginning of a gene
response element
true or false - membrane bound receptors are hydrophobic
false - they are hydrophillic because they are water soluble
what is the name of the enzyme that phosphorylates another protein
protein kinase
what does a first messenger do
it is an extracellular chemical messenger that binds to a specific membrane receptor
how does the second messenger system work
it is a substance that is generated in the cytoplasm of a cell in response to the binding of an extracellular messenger
what are the three subunits of G proteins
alpha, beta and gamma
true or false - GDP and GTP are low energy bonded molecules
false - they are high energy molecules
describe the process of G linked receptor activation
1) membrane bound receptor is bound to the G protein subunits on the inside of cell ; while the ligand binds to the receptor on the outside of cell
2) the alpha subunit is directly bound to the GDP
3) as this happens the G protein changes its structure - the GDP is replaced by GTP and the subunits unbind from the receptor
4) the alpha subunit is then activated and separates from the beta and gamma subunits , with its new GTP
5) these keeps happening as long as there is no phosphorylation
describe the process of G linked receptor inactivation
1) currently, the alpha subunit is bound to GTP but separated from the other subunits
2) when the ligand unbinds from the receptor, GTPase comes in and removes a phosphate from the GTP (hydrolytic activity)
3) all the subunits bind back together and bind to the membrane bound receptor once again
what is the result of the action of G proteins on Ion channels
once the alpha subunit and bound GTP are dissociated, it will move to an ion channel and allow it to open/close
what is the result of the action of G proteins on an enzyme
once the alpha subunit and bound GTP has dissociated, it will move to the enzyme where the stimulatory G protein will stimulate enzyme or the inhibitory G protein will inhibit it
Describe the Action of G-Proteins on Ion Channels
1) the first messenger ligand binds to it’s target receptor - causes a conformational change in the receptor
2) the alpha-subunit’s affinity for GDP decreases and affinity for GTP increases (GDP dissociates and GTP binds)
3) the now GTP and alpha subunit dissociates from the beta and gamma counterparts - GTP alpha subunit moves towards the ion channel
4) depending on previous state of ion channel, it may open or close in response to the GTP-alpha subunit (ion channel will alter the flow of ions into the cell and can affect the electric potential)
Describe the action of G-proteins on Enzymes
1) the first messenger ligand binds to it’s target receptor - causes a conformational change in the receptor
2) the alpha-subunit’s affinity for GDP decreases and affinity for GTP increases (GDP dissociates and GTP binds)
3) the now GTP and alpha subunit dissociates from the beta and gamma counterparts - GTP alpha subunit moves towards the enzyme
4) GTP alpha subunit can become a stimulatory protein (G_s) or an inhibitory protein (G_i)
5) Gs and Gi alter the production of the second messenger (amplifier) in cytosol of cell
Gs _____________ the cAMP second messenger system, while Gi _____________ the cAMP second messenger system.
activates; inhibits
inhibits; activates
activates; inhibits
Gs activates the cAMP second messenger system (STIMULATORY), while Gi inhibits the cAMP second messenger system (INHIBITORY)
Describe the cAMP second messenger system
1) Binding of the first messenger ligand to the receptor causes a conformational change in the receptor
2) the affinity for the alpha subunit for GTP increases (causing GTP to bind and GDP to dissociate)
3) GTP bound alpha subunit dissociates from beta and gamma subunits and moves towards enzyme: adenylyl cyclase
4) adenylyl cyclase is activated (via activation site located on cytoplasmic side of plasma membrane)
5) adenylyl cyclase catalyzes cytosolic ATP -> turns it into cyclic AMP (cAMP)
6) cAMP (second messenger) diffuses through the cytoplasm, binds and activates protein kinase A (PKA)
7) activated PKA catalyzes the phosphorylation of proteins in cell by transferring a phosphate group from ATP to cellular proteins
8) when cellular protein has been phosphorylated -> cellular response
9) cellular response eventually deactivated by conversion of cAMP to non-cyclic AMP via phosphodiesterase
Describe how a ligand-gated ion channel would impact Ca2+ levels
Ligand gated ion channel would undergo a conformational change when activated and allow Ca2+ to enter the cell
Describe how a G-protein would affect Ca2+ levels
1) Once G-protein is activated, it would interact with its effector protein (e.g. calcium channel)
2) calcium channel opens
3) Calcium enters the cell
Describe how calcium is used to develop a cellular response
1) first messenger binds to receptor and causes an increase in calcium entry through the plasma membrane calcium channels
2) receptor is either a ligand gated ion channel or is a G-protein
3) once receptor is activated -> increase in Ca2+ in cytosol
4) Ca2+ in cytosol binds to receptors on ER membrane, ion channel opens, calcium flows out of ER, triggers more calcium release from ER and increases cytosolic [Ca2+] (calcium moves down it’s concentration gradient)
5) when calcium levels inside the cell become high enough, calcium acts as a second messenger
6) calcium binds to inactive calmodulin and activates calmodulin
7) calcium-calmodulin complex activates a calmodulin dependent protein kinase -> phosphorylates proteins in cell -> cellular response!
