proteins 2

Question 1

glycoproteins

where do the bonds take place?

Answer 1

formed from the reaction of a protein with a carbohydrate.
the sugar reacts with either the n-side or the O-side of the amino acid during glycosylation (post-translation)
e.g. immunoglobulines

Question 2

importance of glycoproteins?

Answer 2

1-affect solubility
2-involved in cell-cell recognition
3-affect protein orientation
4-alters signalling
5-stabilises

Question 3

example of glycoprotein gone wrong

Answer 3

Hb1ac. helps determine concentration of glucose in blood over the past 2 months. the higher the conc., the higher the risk of diabetes.
it is a glycated haemoglobin. forms an unstable compound when it reacts with valine and glucose. then undergoes further reaction to form a stable ketamine

Question 4

glycolipids
how is it bound
what properties does it have

Answer 4

covalently or non-covalently bound.
important in transport of water-insoluble fats round the body e.g. HDL and LDL.
Protein helps increase solubility and binds to receptors which break down fat.
High HDL =low heart disease as broken down in liver
High LDL= high chance of atheroma

Question 5

metalloproteins

Answer 5

metal ion attached to protein.

1/3 proteins require it for transport, signalling, enzyme activity, storage.

Question 6

different structures of proteins.

Answer 6

globular-varied functions
fibrous-structural function e.g. tendons, connective tissue
membranous-cell membrane e.g. cell adhesion..

Question 7

haemoglobin

Co-operative binding

Answer 7

4 sub-units. each sub-unit has a haem group at its centre which can carry an 02.
once the first o2 has bound, it makes it changes the shape of the haemoglobin making it more likely for the next 3 o2 molecules to attach.
example of Co-operative binding.

Question 8

sickle cell anaemia

Answer 8

due to single base mutation at 6th position on amino acid chain which causes hydrophilic glutamate to be replaced with hydrophobic valine. this causes haemoglobin to be less water soluble.
as a result, haemoglobin forms crystals at low o2 conc and causes RBCs to crystallise.
o2 released to tissues at lower affinity.

Question 9

collagen

Answer 9

makes up about 25% proteins in the body.
is a fibrous protein.
high tensile strength.
made up of repeat unit ( glycine-x-alanine).
single polypeptide chain forms a coil.
3 polypeptide chains then wrap around this chain and many hydrogen bonds form.

Question 10

when things go wrong with collagen?

Answer 10

scurvy: lack of vitamin C which is used to make hydroxylysine and hydroxyproline. so fewer crosslinks
osteogenesis imperfecta: glycine replaced by larger amino acid, no tight coil, fewer fibrils, disruption of 2-3 structure.

Question 11

LDL receptors

Answer 11

glycoproteins present on surface of all cells.

the positive apoB binds to negative LDL.

Question 12

mutations of LDL

Answer 12

1-no receptors
2-receptors don’t reach surface
3-receptors cannot bind
4-receptors cannot internalise.

Question 13

function of proteins

Answer 13

movement
enzymes
hormones
transport
receptors
control of gene expression 
storage
structural

Question 14

define denaturation

Answer 14

loss of function of a protein