Cellular Form + Function Flashcards
Saccharomyces Cerevisaie
Example of a single-celled eukaryote
contains the regular components of an eukaryote but contains a cell wall
Do all Eukaryotes have a cell wall
No but some do
What is included in an animal cell
Lysosomes and extracellular matrix
Extracellular matrix
specialized material outside the cell
Lysosomes
Degradation of cellular components
Plant cell architecture
cell wall, vacuole, and chloroplasts
Cell Wall
helps with cell shape and protection against mechanical stress
Vacuole
degradation and storage
Chloroplast
site of photosynthesis
Cytoplasm
contents outside the nucleus
includes membrane bound organelles excluding the nucleus
Cytosol
Aqueous par of the cytoplasm
does not include membrane bound organelles
includes ribosomes and cytoskeleton
Lumen
inside of organelles
the lumen is in between two membranes of nucleus
What cellular functions occur at the membrane
- compartmentalization (closed regions of a eukaryotic cell cytoplasm)
- Scaffold for biochemical
- Selectively permeable barrier
- Transport solutes
- Respond to external signals
Membrane Bilayers
Also the lipid bilayer consists of one membrane and two leaflets
The fluid mosaic is made up of proteins and lipids that are able to move around and contains many different types of protein / lipid
What makes up the lipid bilayer
Contains lipid molecule with polar hydrophilic heads and 2 hydrophobic tails that are either saturated/unsaturated
Are lipid molecules amphipathic? What does this mean?
Yes lipid molecules are amphipathic because they contain different biochemical properties
What type of lipids can membranes be composed of?
Phospholipids, glycolipids, and steroles
What is the general structure of phospholipids?
different polar head
phosphate (what makes the lipid a phospholipid
glycerol (what makes it a phosphoglyceride)
2 hydrophobic tails
What is meant by saturated/unsaturated tails?
Unsaturated tails have a little kink to them making them a bit bent.
The unsaturated tails contain a cis-double bond
How do lipids form into a sphere shape?
In its planar lipid bilayer form, the hydrophobic tails are near water so the bilayer will fold until all of the hydrophilic heads are facing water and its tails are protected from water
Cellular membranes are fluid. What does this mean?
“fluid” means that the lipids are able to move around in different ways in the bilayer
What evidence is there to prove that membranes can be deformed without being damaged?
Laser tweezers manipulate the membrane but doesn’t tear or rip
How do phospholipids move?
-Lateral diffusion
- Flex (wobble side to side)
- Rotation (they can spin around)
**rarely they can flip-flop
Why is fluidity important for the membrane proteins
fluidity allows membrane proteins for transportation, enzyme activity and signalling
What happens when membrane changes temperature?
It becomes stiff and less fluidy when membrane is at lower temperatures
How do we fix the issue of viscous membranes
- Phospholipid saturation: making hydrocarbon tail unsaturated with cis bonds making more room in the bilayer
- Shortening the hydrocarbon tails also makes room in the bilayer
Can a membrane that is too fluid be problematic as well?
How do we fix this?
If a membrane is too fluid, it can interfere with cellular functions and the way they fix this is through lipid composition or adding cholesterol to the bilayer
What exactly happens when we add cholesterol to the bilayer?
In the structure of cholesterol, it has a hexagonal structure in between the polar head and single tail. This makes cholesterol very rigid and stiff. Adding this to the bilayer in a 1:1 ratio with phospholipids will decrease the mobility of the phospholipid tails
What is the difference in cholesterol vs phospholipid structure
Phospholipids have a head, glycerol, phosphate, and 2 tails whereas cholesterol has a head, hexagonal stiff planar and 1 tail
Describe how flip-flopping to the other leaflet works
There is a random flip-flopping that happens in the ER through enzymes. SCRAMBLASE that causes rapid flip flopping from cytosolic to ER side so that there is an equal amount of lipids on both leaflets
Why is this random flip flopping necessary?
Because phospholipids are only synthesized on the cytosilic side, we need random flipping to even out the lipids on the ER lumen
Where do lipids get made?
They mostly get made in the ER on the cytosolic side
How do proteins get transported between organelles in the membrane?
- Starting in the ER membrane where random flip flopping is happening and a lipid is formed and facing the lumen side
- The transport vesicle gets snapped off and moves to the the golgi membrane there are specific flip flopping
- This transport vesicle will snap and move to the plasma membrane facing noncytosolic face
How does flip flopping occur?
Random flipping occurs in the ER with the help of scramblase
Specific flipping in the golgi membrane through enzymes flippase
after golgi membrane no flipping happens
What are Glycolipids and glycoproteins
lipid/proteins that have sugars attached to them
How do these glycolipids/proteins form?
In the golgi membrane a sugar is added to lipids/proteins on the luminal face
Orientation of these glycolipids
They always face luminal/non-cytosolic face
Summarize the fluid mosaic model and how lipids move?
- The fluid mosaic is made up of a bilayer with lipids that contain polar heads and 2 hydrocarbon tails
- They can include phospholipids, sterols, or glycolipids
- They can diffuse laterally, flex, rotate, and rarely flip-flop
- Fluidity can be maintained through alterations to hydrocarbon tail length and its saturation and also by adding cholesterol
- Random flip-flopping also occurs by enzymes, scramblase that properly and evenly distribute lipids
Asymmetry of the lipid bilayer
Within the cytosolic face that is where lipids are made in the ER and the non-cytosolic face and luminal face is where sugars attached to proteins are facing.
There is specific flip-flopping that happens in the golgi membrane
What is the difference between integral and peripheral membrane proteins
Integral membrane proteins insert some way into the membrane
Includes transmembrane, monolayer associated and lipid-linked
Peripheral membrane are proteins that interact with other proteins that insert into the membrane. These associations are made non-covalently
What exactly are membrane proteins?
They carry out a lot of functions within the membrane and are associated with the lipid bilayer in a variety of ways
Briefly describe the different types of integral membranes
Transmembrane are proteins that pass entirely through the membrane on both sides
Monolayer: only associated with one side of the lipid bilayer
Lipid-linked: This is where proteins are attached to lipids and these lipids are inserted into the membrane
How are proteins and lipids attached in lipid-linked membrane proteins?
They are covalently bonded to one another
How do protein-attached membrane proteins interact with the membrane?
These proteins bind to either other proteins or lipids through non-covalent interactions
Transmembrane protein properties
Because they pass entirely through the membrane, these proteins are amphipathic, the sides that hang outside the extracellular space are hydrophilic and their AA side chains are polar
The portion that is located within the bilayer is hydrophobic and AA side chains are non-polar
X-ray Crystallography
Method that shoots x-rays at proteins to crystalize them and based on the defracture you can determine its structure
Hydrophobicity plots
Easier method for identifying membrane proteins.
The y-axis, hydropathy index ranges from hydrophilic (bottom) to hydrophobic (top)
The x-axis is the amino acid number
To figure out the structure of a M.P. we want to look for 20-30 amino acids in a row. These hydrophobic AA gives us the curly coil that we see in an a-helix
Why are proteins anchored by amphipathic a-helix in monolayer M.P?
Due to the fact that these proteins only interact with one side of the bilayer, it needs to be secured to the membrane somehow and these proteins are secured through hydrophobic AA side chains of the a-helix binding to the hydrocarbon tails
What types of anchors are present in lipid-linked M.P?
GPI anchor that is synthesized in the ER and ends up on the cell surface
Lipid anchors that direct proteins to the cytosolic face. The cytosolic enzymes catalyze this process
How can you extract membrane proteins using detergents?
Detergents have a single hydrocarbon tail (micelle) which interact with the lipid tails and separate the membrane proteins from the lipids
How can lateral diffusion of MP be studied?
Tagging a protein with GFP and then photobleaching a portion of the protein white and then measuring how quickly the white spot turns green again
The speed will show how fast proteins move in the bilayer
