Cellular Membranes Flashcards by Anna Safrankova

Why are cellular membranes called ‘amphiphillic’

Both hydrophobic and hydrophilic regions

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Give the 3 functions of plasma membranes

For receiving info from other cells eg using glycoproteins

A barrier to extra cellular molecules eg ions

For movement and expansion of a cell

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What can pass though membranes via simple diffusion

Very small polar molecules like H2O

Hydrophobic (non polar) molecules like co2 and 02 , urea

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What can’t pass through lipid membrane

Charged ions like NA, ca2+ (polar)

Large molecules like glucose and amino acids

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Explain the 3 parts to cholesterol structure

A hydroxyl OH head which is hydrophilic
Steroid rings (carbon)
And a fatty acid hydrophobic tail

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Explain cholesterols function and how it performs it and why is it important

Cholesterol interferes with movement of fatty acid tails vis their rigid steroid rings

This is important as it reduces permeability which some transporters and enzymes depend on less fluidity

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Name the 4 major phospholipids

Phosphatadyl ethanolamine

Phosphatadylserine

Phosphatadylcholine

Sphingomyosin

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What is sphingomyosin made of

A sphingosine with a phosphate and choline attached

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Which side of the membrane are glycolipids found

Apical (extra cellular side)

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Name the 2 main types of glycolipids and their differences

Galactocerebroside - 2 fatty tails, glycerol, and 1 GALactose

Ganglioside - same structure but 3X GAL , GLU, NANA(cialic acid) , 1x GAL nac

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Name the 4 types of membrane proteins

1- transporters - move nutrients and metabolites

2- linkers - link extra/intra molecules to the membrane eg cytoskeleton

3- receptors

4- enzymes

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What are the 3 groups of proteins on membranes showing diversity

1- integral - permanently attached eg transporters

2- lipid anchored proteins - covalently bonded to lipids in membrane EG GPI PROTEINS

3- PERIPHERAL - only associated temporarily to a specific membrane protein (dissociate eg when extreme ph)

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How are lipid anchored proteins attached to each other

By covalent bond

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What are the 2 modes of passive transport

Transporter mediated (transporter/carrier)

Channel mediated (channel protein)

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3 types of active transport / energy driven

1- coupled/cotransport

2- atp driven (hydrolysis of atp used)

3- light or redox driven - eg in chloroplasts

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What is the glycoxalyx

A cell coat which is formed by glycolipids and glycoproteins

Made of oligosaccharides

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Why are glycoproteins very important

N glycans - allow protein folding no aggregation
Mucins production- lubrications for cell signalling

Proteoglycans-

Cell to cell adhesion in matrix
Growth factor binding (proliferation)
GAG to provide a gel for connecting joints

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4 functions of the glycocalyx

Protection - from unwanted interactions

Storage - of proteins like growth factors which then are released (why glycoproteins promote metastasis)

Adhesion - carbohydrates and proteins/lipids

Recognition- cells have specific glycolysation

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Why is glycocalyx used as recognition of cells

Different cells have specific glycolysation patterns

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Name the 3 types of glycoproteins and the amino acid they bind to

N- glycans. Bind to asp(N)

O glycans - bind to serine or threonine via a oxygen bond

Proteoglycans - bind to serine

What oligosaccharide to all glycans have in common

Acetyl glucosamine

Either N or O

What is the repeated units attached to proteoglycans called and made of

Glycosaminoglycans (GAG)

Amino acid sugar

Uronic sugar

Which experiment first found that membrane proteins had ability to move around membrane

FRAP - flurescent recovery after photobleaching

What did frap find

That proteins differ in diffusion ability

In a tight stack of cells some proteins are separated in either apical or basal membrane sides. Why is this

Tight junctions between cells mean polarisation of proteins

Why is the polarity of proteins in membranes important for co transport

At the apical side, the na+ co transporter is needed to carry glucose from lumen At the basal membrane the na pump and the glucose transporter is needed

There are 4 ways of constructing protein mobility , what are they

1- self assemble together (aggregation) 2) macromolecules tether proteins outside of the cell (extracellular) 3) macromolecules tether proteins on basal side in cytosol 4) cell to cell protein interaction (joining of cells)

How is the cytoskeleton an example of the protein mobility restrictions in the red blood cells

Proteins are associated with the cytoskeleton network (spectrin protein) which restricts their movement Free protein membranes eg trans membranes are also restricted in the cytoskeletoncomplex

There are 3 ways proteins can be membrane bending - explain

1) proteins can bind to large phospholipid heads to cluster them = bending 2) rigid bent proteins attach to the membrane 3) hydrophobic protein domains are attached into the membrane bending it

Why is bending of membranes important (3 ways)

Membrane trafficking (exo and endo) Cell division

What are GPI proteins an example of and what kind of roles do they have

GPI are lipid anchored proteins Attached to phosphatidylionisitol lipids Can act as receptors etc

How did FRAP work

Proteins were modified to be GFP proteins that bound to membrane proteins Found difference in diffusion in different proteins on membrane

How do gangliosides act as entering points for cholera

Cholera binds to the cell surface receptor ganglioside and enters cells. This causes devastating impact

Why does protein kinases in signalling need phosphatidylserine on the basal side? (Showing importance of asymmetrical bilayer)

Negative charged phosphate is needed to activate proteins in cellular response

What are mucins needed for produced by n glycans

For protection at epithelial cells And for lubrications for cell signalling

Why is n glycans in particular important for viruses to survive

Their spike proteins are glycosylated which prevents binding of antibodies and they can bind to surface receptors

What are glycolipids made of and name the 2 major types and charges they have

They are made up of sphingosine and also attached covalently to oligosaccharides such as galactose Galatocerebrosides are neutral with a galactose Gangliosides are negative in charge and have a sialic acid

Explain the 3 functions of the glycolipids

1- they determine blood group by their saccharides. Eg antigen A is a gal nac is added by glycosyltransferases and B antigen is just gal 2- they are entry points for some bacteria and toxins such as cholera has gangliosides as a receptor 3- they are involved in cell to cell interaction eg the inflammatory response. They attach to lectin proteins which allow for wbc to enter inflamed tissues

What are the main functions of n glycan glycoproteins

1- they produce mucins important for lubrication for cell signalling 2- they allow folding of proteins correctly 3- they are important for viruses as they coat spike proteins to stop antibodies

What is the structure of a proteoglycan

Serine attached protein to a tetrasacharide and gag (uronic acid and amino acid sugar)

Why are GAGs important making proteoglycans important

They form gel mesh in the matrix which can withstand compression eg in joints such as knees

How can mutation to proteoglycans cause metastasis

They are growth receptor factors = cell proliferation

How can proteoglycans also help in inflammatory response / cell cell interaction aswell as glycolipids

They can bind to lectin proteins

What are aggrins and their job?

They are proteoglycans which act as receptors on NMJ and on Tcells They allow lipid clustering - acH and Tcells receptors cluster which allows for Tcells activation in immunity and also for muscle contraction

Why would mutation to proteoglycans stop immune system

Aggrins needed to cluster Tcells receptors for a response from the antigen presenting cell

Name the 2 aggrins types

Musk LRP4

Why are transmembrane proteins called amphipillic

Both a hydrophilic region (polar side chain not inside membrane) Hydrophobic region inserted in the membrane eg valine side chain

Why do unsaturated cis fatty acids cause fluidity

Became shorter and less tightly packed due to kinks

What do linker proteins do

Link cytoskeletal filaments like actin IF and microtubules and nuclear lamins