structure of cell membrane - matteus de silva

Question 1

Nuclear envelope

Answer 1

membrane enclosing the nucleus . the protein lined pores allow material to move in and out

Question 2

chromatin

Answer 2

DNA plus associated protein

Question 3

nucleolus

Answer 3

condensed region where ribosomes are formed

Question 4

peroxisome

Answer 4

metabolises waste

Question 5

rough endoplasmic reticulum

Answer 5

associated with ribosomes ; makes secretory and membrane proteins

Question 6

smooth endoplasmic reticulum

Answer 6

makes lipids

Question 7

microtubules

Answer 7

form the mitotic spindle and maintain the cell shape

Question 8

centrosome

Answer 8

microtubule organising centre

Question 9

intermediate filaments

Answer 9

fibrous protein that hold organelles in place

Question 10

microfilaments

Answer 10

fibrous proteins that form the cellular Cortex

Question 11

lysosome

Answer 11

digests food and waste material

Question 12

Golgi apparatus

Answer 12

modifies proteins

Question 13

mitochondria

Answer 13

produces energy

Question 14

functions of the cell membrane

Answer 14

protective barrier
contains cytoplasm (fluid in cell)
regulated transport in and out of cell (selectively permeable)
interlocking surfaces bind cells together
allow cell recognition
provide binding site for enzymes
provide anchoring sites for filaments of cytoskeleton
receives signals from outside the cell for internal cellular activities
imports and exports molecules
movement of the cell

Question 15

general structure of the cell membrane

Answer 15

a lipid bilayer that contains 2 sheets of lipids inter dispensed with proteins

Question 16

Lipid structure

Answer 16

hydrophilic head- H2O loving due to polar group in the head
hydrophobic tail - H20 hating due to the long hydrocarbon tail

Question 17

Amphiphatic molecules

Answer 17

contain both hydrophobic and hydrophilic parts

Question 18

Lipids

Answer 18

most abundant lipid is the phospholipid
phospholipids have a PO4 group in the third OH- group of the glycerol instead of hydrocarbon
this can attach a hydrophilic group
- choline - phosphylicitycholine
-polar amino acids like serine - phosphatidylserine

Question 19

properties of the lipid bilayer

Answer 19

due to the amphiphatic property of the membrane can reseal after an ‘injury’
bilayer is fluid - the orientation of the lipids and the outer aqueous surroundings keep the lipids in the bilayer
- the lipid can move around the layer
not the same as flexible - entire membrane being bended

Question 20

importance of hydrocarbon on properties of layer

Answer 20

hydrocarbon tail will determine the fluidity of the membrane just as it does in fats and oils
two components are important
^the length of the hydrocarbon chain
- 14 to 24c but usually 18-20 present
^level of unsaturation (number of double c bonds)
- 1 tail has 1 or more double c bonds
- other tail is saturated

Question 21

membrane fluidity

Answer 21

enables the membrane proteins to diffuse rapidly . simple means of distributing lipids and proteins allows membranes to fuse with one another . evenly distributed during daughter cell formation

Question 22

cholesterol in the membrane

Answer 22

cholesterol is added to areas that have lots of unsaturated lipids to help fill in the gaps between the tails
helps to stiffen and stabilise the bilayer
> less fluid and less permeable

Question 23

vesicles

Answer 23

the size of the membrane is increased and decreased with the interaction of vesicles . vesicles bringing material to the membrane to be secreted . increase the surface area of the plasma membrane and through the process of endocytosis , the surface area of the cell membrane decreases

Question 24

endocytosis

Answer 24

process in which a substance gains entry into a cell without passing through the cell membrane .
results in the formation of an intracellular vesicle by virtue of the invagination of the plasma membrane
example : antibodies

Question 25

phagocytosis

Answer 25

process by which some living cells ingest or engulf other cells or particles the phagocyte may be a free living one celled organism such as an amoeba , or one of the body cells such as a white blood cell example : white blood cell engulfing bacteria

Question 26

pinocytosis

Answer 26

small particles suspended in extracellular fluid are brought into the cell through an invagination of the cell membrane

Question 27

receptor- mediated endocytosis

Answer 27

binding of ligands allow uptake of specific molecules example cholesterol intake: low density lipid proteins bind cholesterol and carry it in the blood LDL's act as ligands binding receptors on cell surface and cholesterol is taking into the cell

Question 28

exocytosis

Answer 28

exocytosis is the process by which cells move materials from within the cell into the extracellular fluid exocytosis occurs when a vesicle fuses with the plasma membrane , allowing its contents to be released outside the cell requires atp for the active transport example : cell expels chemical transmitters such as hormones example : insulin being released by pancreas cells using exocytosis

Question 29

functions of cell membrane proteins

Answer 29

transport enzymatic activity intercellular joining attachment to the cytoskeleton and extracellular matrix signal transduction cell-cell recognition

Question 30

Proteins

Answer 30

integral/trans membrane -proteins that cross both layers of the phospholipid bilayer peripheral -proteins that are only on the top half or the bottom half of the phospholipid bilayer

Question 31

trans-membrane proteins carry out the function

Answer 31

transporters- na+ pump to move na+ across linkers - integrins to link intercellular components to extracellular ones receptors - to bind a compound that sends a signal to the rest of the cell enzymes - perform chemical reactions in the membrane

Question 32

association with the membranes

Answer 32

transmembrane - span the entire membrane linked by lipids - on either surface of the membrane interaction with transmembrane proteins

Question 33

integral membrane proteins

Answer 33

are amphiphatic , in that they have hydrophilic and hydrophobic regions that are oriented in the same regions in the lipid bilayer examples : na+-k+ ATPase glucose permeate hormone receptors ion channels and gates histocompatibility antigens certain enzymes of the electron transport chains gap junction proteins

Question 34

single transmembrane segment proteins

Answer 34

usually alpha-helical = 20-25 residues , mostly non polar example : glycophorin of the erythrocyte , antibodies

Question 35

multiple transmembrane segment proteins

Answer 35

7 alpha helix motif is very common example : highly selective potassium ion channel

Question 36

membrane spanning regions can also be beta barrel structure

Answer 36

multiple trans membrane segments form B sheets that line a cylinder example : porins (non specific bacterial channels )

Question 37

peripheral membrane proteins

Answer 37

associated with membranes but do not penetrate the hydrophobic core of the membrane . found in association with integral membrane proteins examples : the NADH-CoQ reductase complex of enzymes and cytochrome c reductase complex of enzymes are integral membrane proteins of the mitochondrial electron transport chain