cell and membranes Flashcards
how do dyes help biologists
give a better picture of cells and their insides
how were dyes used in the brain
black dye showed separate neurones in the brain, showing the brain was made of different cells
what is the zymogen granule
specialised organelle in pancreatic acinar cells for digestive enzyme storage and secretion.
what is a tight junction
a junction between animal cells which ensure a watertight seal between two adjacent animal cells. Made of transmembrane proteins which interlink both plasma membranes.
what are desmosomes
Junctions which resist tearing by a protein called cadherins which connect the cytoskeleton filaments in each cell.
what is a gap junction
channel connecting cells made of tubes called connexins
what do gap junctions do
allow passage of electrical and chemical stimuli. this synchronises contractions of smooth muscle responsible for peristaltic movements. and cardiac
what is the extracellular matrix
composed of proteins and polysaccharides which are secreted locally and form a meshwork with the cells.
how do plant cells communicate
through plasmodesmata
what is a protein channel
membrane proteins with a hydrophilic opening which allows hydrophilic molecules to pass through, most are gated
what is a carrier protein
membrane protein which changes shape when a molecule binds to it, letting the molecule inside.
what carrier protein allows glucose to diffuse
Glut1
how is the glucose gradient maintained
glucose is phosphorylated which means that glucose cannot travel back through Glut1
what are the three main ways that active transport takes place
coupled transporter
ATP driven pumps
Light-driven pumps
what are coupled tranporters
when the transport of one solute is coupled with another to allow movement against gradient. (secondary)
what are ATP driven pumps
when energy from hydrolysis of ATP is used
why must the electrochemical pump be maintained
if ions flowed down their gradients, this would affect osmotic balance
movement of ions like Na drives movement of other substances
how does the Sodium potassium pump work
pumps 3 Na out and 2 K in against conc gradients. Does this by phosphorylation
what is an example of secondary active transport (symport)
sodium glucose symporter where glucose is coupled with sodium to allow glucose to flow against conc gradient
example of antiport
diffusion of na into cardiac muscle allows ca to leave, this is important in regulating contraction
how does digoxin work
this inhibits the sodium potassium pump, increasing the levels of sodium in cells and therefore the sodium calcium antiport is less effective so more calcium inside the cardiac muscle for a contraction
how do tight junctions play a role in membrane proteins
prevent movement of proteins such as symporters away from where they are needed.
why are cells typically small
to maintain a high surface area to volume ratio
what methods can be used to see cells
staining, immunostaining and fluorescence microscopy and fluorescent protein tagging
what gives cells their shape
cell wall and cytoskeleton
where are the ribosomes made
in the nucleolus
outline lysosomes
example of compartmentalization which contain lots of catabolic enzymes in an acidic environment
they also have a role in autophagy
digestion of both external and internal bodies
What is Lysosome storage disease
where a key enzyme is not working and so material accumulates in the lysosome.
how do we know all eukaryotic cells are related
genes that are conserved across eukaryotes leave no doubt we come from a last eukaryote common ancestor
how is gene expression different in prokaryotes to eukaryotes
translation and transcription are coupled in prokaryotes but in eukaryotes they are separate
what is different in eukaryotes with gene expression
RNA can be modified by splicing
what is the transmembrane domain
the part of an integral protein which goes through the membrane
integral vs peripheral proteins
integral have a part of the protein which passes through membrane but the peripheral proteins arent inserted in membrane
may be attached by a lipid or by protein interactions
why is a fluid membrane important
allows fusing with other membranes such as vesicles
ensured membrane is equally shared in cell division
cell migration requires fluid membrane
how is the membrane fluidity demonstrated experimentally
using laser beam and bleaching
dye the lipids then bleach a part of the membrane using a laser
this will prevent the fluorescence
but when left for some time, it returns, showing lipids have moved around
how do lipids move in the membrane
by rotation, flexion and flip flop
what enzymes does flip flop require to work
flipases and flopases
what enzymes does flip flop require to work
flipases and flopases
what is the problem for pure phospholipid bilayers
they experience rapid phase change over a narrow range of temp
how do prokaryotes control membrane fluidity
they synthesise more lipids with smaller chain length and unsaturation in order to decrease van da walls when it is cold. this increases spacing between molecules
reverse when temp increases
how do eukaryotes regulate the membrane fluidity
using cholesterol
at 37 degrees the membrane would be too fluid so it stabilises interactions between phospholipids
at lower temperatures, it prevents the molecules from getting too close and becoming hard and immobile
what prevents proteins from moving too far along the membrane
tight junctions
how does number of tails influence membrane shape
two tails forms a cylinder structure and will form a bilayer
1 tail forms a cone and will interact into a micelle
how is membrane asymmetry maintained
scramblases (passive) and flipases and flopases
flipases bring PS and PE onto cytosolic side
flopases bring SM and PC onto the exoplasmic side
outline scramblases
new lipids are only added on the cytosolic side so this must be scrambled
scramblases arent specific and transfer phospholipids from one side to the other
