Cell Biology Midterm 2 Flashcards
What are the functions of the Plasma Membrane? (4)
Maintain ion and chemical gradients
Control material exchange between cells and its environment
sense and control communication
Malleable: able to change shape
What are membranes composed of?
Lipids and proteins!
What are the membrane lipids? (2)
- Phospholipids
A.Glycerophospholipids: uses glycerol for backbone
B. Sphingophospholipids: uses sphingosine for backbone - Sterols
What is the structure of a glycerophosphoipid?
Glycerol backbone
ESTERFIED two fatty acid chains attach to glycerol (Hydrophobic)
The 2 fatty acid chain is cis-unsaturated (kinky) reduce packing and rigidity
Phospho-head group linked to glycerol (hydrophilic)
What are the major types of phospholipids? (5)
PhosphatidyETHANOLAMINE
PhosphotidylSERINE
PhosphatidylCHOLINE
SphingoMYELIN
SphingoSINE
Why is cholesterol a major component of membranes?
STERIOD RING IS HYDROPHOBIC
It is between fatty acid chains of phospholipids
It increase packing of phospholipids and decrease permeability of water
What movement occurs in phospholipid bilayers?
Lateral Diffusion
Flexion
Rotation
Flip-flop (rare)
Is transbilayer diffusion of lipids favourable?
No its slow.
Lateral diffusion is FAST and favourable
What are membrane rafts?
Parts of the membrane that are ENRICHED in specific lipids: Saturated lipids, cholesterol
PACK WELL
What intermolecular force does saturated lipids have?
Van der Waals Attraction
What phospholipid is faceing outwards from the cell membrane?
PhosphatidyCHOLINE
SphingoMYELIN
What phospholipid is facing inside the cytoplasm?
PhosphatidylETHANOLAMINE
PhosphotidylSERINE
Why is it important for the membrane to maitain their ASSYMETRY?
Bc loss of PS asymmetry leads to programmed cell death APOPTOSIS
Glycolipids asymmetry is responisble for BLOOD TYPES
What happens why PhosphotidylSERINE is on the cell surface (not suppose to be there)?
Cell will undergo apoptosis
Cause a disease: Antipholipid syndrome
genetic mutation alters proteins
Auto-immune
What are signaling molecules?
varity of molecules that are attach to membranes to regulate cell function
What are the four types of intergral membrane proteins?
Transmembrane alpha helix; multiple pass
Transmembrane alpha helix; single pass
Transmembrane; beta sheet; multipass
Partial Insertion; amphiphilic alpha helix
What proteins covalently modifies proteins with glycolipids (sugar+lipid=glycolipoprotein)
- Lipid-anchored proteins: Covently modified proteins with lipids
- Peripheral membrane proteins: bind non-covalent to transmembrane and/or membrane lipids.
What are the 3 types of covalently attached lipid anchors?
Myristoyl achor
palmitoyl anchor
Farnesyl anchor
What can causes a certain alpha-helices to become a transmembrane domain?
-most transmembrane proteins cross membrane as a hydrophobic alpha-helix
-Usually 20-30 amino acids long to span the lipid bilayer
-Hydrophobicity can be measure in a hydropathy plot
What is a hydropathy plot?
How much a single/multi pass transmembrane protein FREE ENERGY is associated with moving an amino acid from OIL to water
What is a Bacteriohodopsin?
is a seven transmembrane alpha helix protein in BACTERIA
capture light to pump H+ out
Make H+gradient to drive ATP production
Was covalently Modified by RETINAL
Photons change retinal shape
What is a disulphide bond? (only bond in extracellular space)
Cysteine amino acid residues react to each other to form sulphur to sulphur bridges.
HELPS STABLIZE PROTEIN SHAPE
What is glycosylation?
Covalent addition of oligosaccharides to proteins
Where are most plasma membrane proteins mostly glycosylated on?
SERINE OR ASPARAGINE RESIDUES
What is a glycocalyx?
Its glycosylated proteins coated on the cell surface. (sugar polymers)
Allows cell to adhere to the matrix and to other cells.
GIVES IDENTITY TO CELL
What can FRAP do?
Determine lateral diffusion of membrane proteins
What is free or unrestrained diffusion?
a proteins can FREELY move across the PS.
FRAP: rapid recovery of fluorescence
What is No or negligible diffusion?
A protein is completely immobile or its diffusion is slow
FRAP:slow to no recovery of fluorescence
What is restricted or partial diffusion?
protein is FREE to DIFFUSE BUT only within a subsection of a membrane
What are the three subdomains of a sperm?
Anterior head
posterior head
TAIL
use restricted diffusion
What are mechanisms to restrict membrane protein movement?
self-assemble into large complexes
Tethered to the cytoskeleton inside cells
Tethereed to the extracellular matrix
interact with proteins on another cell.
What is the red blood cell biconcave?
Due to membrane protein interactions with a spectrin cortial cytoskeleton
What is spectrin? (peripheral membrane protein)
A protein similar to actin that forms a mesh like struction UNDER the cytosolic face of PS.
what is a glycophorin and BAND 3?
two diff integral membrane proteins that binds spectrin, link “skeleton” to membrane
What does the junction complex include?
It includes a filamentous actin and it is attached to the membrane by the transmembrane GLYCOPHORIN PROTEIN
What are corrals?
spectrin cortical cytoskeleton fenced off the plasma membrane into compartments
What is the cortical cytoskeleton?
membrane domains that restrict protein diffusion (small corrals)
How can protein diffusion be restricted?
Restricted within small corrals
restricted from moving between apical and basolateral membranes in epithelial or endothelial cell layers
What happens in the G1 phase?
Preparation of cell for DNA replication
What happens in S phase?
DNA replication
What happens in G2 phase?
cell growth (size, biomass, materials)
What happens in M phase?
Sorting of materials (chromosomes, organelles) TO PREPARE TO SEPERATE
Separation of cell into two daughters cells
M-phase: prophase
Chromosomes condense,
mitotic spindle assemble
M-phase; prometaphasr
BREAKDOWN of nuclear envelope
ATTACHMENT of chromosomes to spindles
M-phase: metaphase
ALIGNMENT of chromosomes
M-phase: anaphase
Sister chromatids separate
Pulled towards spindles
M-phase: telophase
full set of DAUGHTER CHROMOSOMES arrive at spindle
Contractile ring pinch the cytosol
Nuclear membrane begins to re-form
M-phase: cytokinesis
SEPERATING INTO TWO CELLS
CONTRACTILE RING SQUEEZE to form TWO DAUGHTERs
Generates a cleavage furrow, represent final stages of separation
What can a Cdk do?
Cycling dependent kinase can phosphorykate several different substrate proteins
What is the switch mechanism to turn the Cdk on them?
Binding to one of several specific cyclin proteins
What does M-Cdk trigger??
CONDENSIN (protein complex)
Cause condensation of chromosomes
Forms mitotic spindle
What does M-Cdk activate?
Starts at Mitosis and is removed to finish mitosis
What is the APC/C ?
A protein complex that is required to allow metaphor to anaphase transition
Leads to degradation of M-Cdk
Why is control good?
Cyclin-Cdk acts as a timer, cause removal of cycling
Some cases cause upregukation of cyclin
What triggers G1-Cdk?
favorable extraceller environment
What triggers G1/S-Cdk and S-Cdk
DNA damage
What triggers M-Cdk?
Unreplicated DNA And DNA damage
What triggers APC/C-Cdc20
Chromosome unattached to spindle
How can some Cdks be good? (before mitosis)
They are effective has cancer drug targets!
Such as
-matastatic breast cancer
-pancreatic cancer
-other cancer
When does the mitotic spindle begin?
Assemble in EARLY mitosis. (PROPHASE)
What is the mitotic spindle?
A BIPOLAR array of microtublues. Involved in seperation of chromosomes and materials.
What is a spindle pole?
has a centrosome and other components. Has three types of microtubules,
ASTRAL microtubules
KINETOCHORE microtubules
INTERPOLAR microtubules
What is ASTRAL microtubules?
from spindle pole to cell cortex. Helps ANCHOR spindle poles.
What is KINETOCHORE microtubules?
From spindle pile to CHROMOSOME (attach to kinetochore)
What is INTERPOLAR microtubules?
From spindle pole to interpolar microtubule coming from other spindle
How does a cell know when it is time to proceed from metaphase to anaphase?
In metaphase, ALL CHROMOSOMES SHOULD BE ATTACH TO KINETOCHORE MICROTUBULES.
-prevent improper sorting during cell division
The metaphase to anaphase transition checkpoint sense if there is no free kinetochore remaining. APC/C
What drugs target the mitotic spindle assembly? (cancer therapy)
PACLITAXEL AND DOCETAXEL
- bind and stabilize microtubles, prevents assembly of mitotic spindle
-trigger metaphase-anaphase checkpoint arrest
What types are passive transport? (2)
- channel mediated (continous pore)
- transporter-mediated
What types are active transport? (3)
- coupled transporter
- ATP-driven pump
- light-driven pump
What happens to the membrane when charged solutes are transported by passive transport?
created a electrochemical gradient (membrane potential)
Helps molecules move by faciliated diffusion
What are the conformational states during passive transport?
Outward-open
occluded
inward-open
What are the 3 couples transporter pump?
Uniport- only 1 molecule in
Symport- 2 molecules can go in same direction
Antiport- 2 molecules can go in opposite directions
What does Na+ glucose symporter do?
recover glucose from extracellular medium before excretion.
Glucose is passivly diffused by the electrochemical gradient of Na+
What does ATP-Driven pumps do?
membrane transport enzymes that use energy released by ATP HYDROLYSIS to drive transport
What are the types of ATP-driven pumps? (4)
- P-type-transport IONS
- ABC transporter- Transport small molecules
- V-type proton pump- transport H+ and CONCUSME ATP
- F-type ATP synthase- transport H+ and makes ATP
How does P-type Na+ K+ pump work?
Exchange 3 Na+ to 2K+
IT IS ELECTROGENIC
drives electrical currect accross the membrane
What does P-type Na+ K+ control ?
CONTROL OSMOLARTIY
the Na+ electrochemical gradient draw Cl- and balanced the inter and extracellular
What are the gating mechanisms of ion channels? (4)
Voltage gated
Ligand-gated(extracellular)
Ligand-gated (intracellular)
mechanically gated
What are the functions of channels?
regulate electrical signals in neurone
regulate neuron to neuron communication
muscle contraction and senses
leaf-closing response
MEMBRANE POTENTIAL
How does a K+ channel select K+ and excludes Na+?
Bc there’s a bacterial K+ channel
Four subunits
-negative charges on CYTOSOLIC side allows +ve ions to pass
-Vestibule is a hydrating area (H2O bound ions)
-Pore helix also selects for +ve ions
-Selectivity filter allows only K+ to pass
What is an action potential?
signal is a change in MEMBRANE POTENTIAL that goes a long the length of the neuron
What is the process of an action potential?
short, local DEPOLARIZATION of the plasma membrane that migrates along the axon
MORE POSITIVE OR NEUTRAL MEMBRANE POTENTIAL
controled by VOLTAGE GATED CATION CHANNELS
What is happing to the electrochemical gradients during action potential>
Before AP: Lots of Na+ OUTSIDE
Lots of K+ INSIDE
During AP: Na+ rush IN
Na+ channels openning
How is membrane polarity reestablished?
Voltage gated Na+ channels INACTIVATION
DELAYED VOLTAGE GATED K+ CHANNELS
k+OUT and Na+ INN CELL
What are the types of glial cell
Schwann cells enclose PERIPHERAL NERVES
Oligodendrocytes enclose nerves of the CNS
What is a neuronal synapse
neurons form contact sites with other neurons
permind UNIDIRECTIONAL chemical communication between cells
Whats happens when an action potential is activated? (6 steps)
- It activates voltage-gated Ca+2 channels to open the presynaptic neurone.
Ca+2 cause secretion of ACETYLCHOLINE
- ACETYLCHOLINE binds and OPENS acetylcholine receptors, causing Na+ to enter and DEPOLARIZE Cell
- nearby voltage-gated Na+ channels open to further DEPOLARIZE and speak action potential in MUSCLE CELL
- plasma membrane voltage-gated Ca+2 channels open ALLOWING Ca+2 to enter cells
- Sarcoplasmic reticulum voltage gated Ca+2 channels open to release stored Ca+2 into cytosol
- VERY LARGE SPIKE IN CYTOSOLIC CA+2 CAUSES MUSCLES TO CONTRACT
What are the 2 membrane transport proteins?
Channels
Carriers or permeases (Active and Passive)
Are all membrane transport proteins MULTIPASS INTEGRAL membrane proteins?
YES
What is the electrochemical gradient?
A net driving force that consist of concentration and ELECTRON POTENTIAL DIFFERENCE
What can remove integral membrane proteins?
DETERGENTS
What can remove peripheral membrane proteins?
CHANGES IN PH AND SALT
What is a P-type pump?
Self-phosphorylate and transports ions
MAINTAIN ION GRADIENTS ACCROSS MEMBRANWS
wHAT are membrane rafts?
PARTS OF MEMBRANE ENRICHED IN SPECIFIC LIPIDS: SATURATED LIPIDS AND CHOLESTORL
What are two examples of membrane proteins?
Bacteriorhodopsin, and GLYCOPHORIN
What is the partial repolarization stage?
Closing Na VOLTED gated channels
What is complete repolarization stage?
Closing K+ VOLTED gated channels
Activity of the sodium-potassium pump
K+ leak channels