Carbohydrates

Question 1

what are the functions of carbohydrates?

Answer 1

-storage
-energy source
-structural
-inter-cellular communication

Question 2

what is the general formula of carbohydrates?

Answer 2

(CH2O)n

Question 3

what structure do larger monosaccharides have?

Answer 3

form ring structures

Question 4

what are six and five member rings called?

Answer 4

-five: furanoses
-six: pyranoses

Question 5

how can you differentiate between aldoses and ketoses?

Answer 5

-if oxygen is on an aldehyde, it is an aldose
-if oxygen is on an a ketone, it is a ketose

Question 6

which stereoisomers do carbohydrates form

Answer 6

Form D- and L- stereoisomers

Question 7

which stereoisomer is naturally found?

Answer 7

D-stereoisomer

Question 8

what other shape can sugars be found (apart from rings) and why?

Answer 8

can form chair conformation because of the spread of electrons

Question 9

two different anomers can exist, why and what is the importance of this

Answer 9

why = depends on orientation of OH group on anomeric carbon (carbon 1)
important because the orientation of OH group determines the shape of the molecule when sugars bind to each other

Question 10

which 2 anomers exist?

Answer 10

OH group can be across from each other (equatorial)
or
OH group can be down from each other (axial)

Question 11

how is a glycosidic bond formed?

Answer 11

when two monosaccharides join together in a condensation reaction

Question 12

what does a glycosidic bond being beta or alpha depend on?

Answer 12

the orientation of the OH group

Question 13

which other chemical groups can carbohydrates contain?

Answer 13

-phosphate
-amino
-acetyl

Question 14

how can other chemical groups affect carbohydrates?

Answer 14

-changes properties e.g. charge

Question 15

describe glucosaminoglycans

Answer 15

-unbranched polysaccharide made up of repeating disaccharide units that contain a hexosamine and uronic acid
-highly polar and attract water

Question 16

how do disaccharides differ?

Answer 16

-types of monosaccharide
-nature of bond

Question 17

what is an oligosaccharide?

Answer 17

-more than two but less than a lot (maybe 6) monosaccharides

Question 18

describe O-linked glycosylation

Answer 18

-attachment of sugar molecule to oxygen atom of certain amino acids
-this is a post-translational modification
-clustered in proteins
-has protective role e.g. mucin

Question 19

describe N-linked glycosylation

Answer 19

-attachment of oligosaccharide to nitrogen atom of certain amino acids
-spread through protein
-more variable
-has effect on protein folding, activity and cellular location

Question 20

what is mucin?

Answer 20

a glycoprotein constituent of mucus

Question 21

what is the difference between homopolysaccharides and heteropolysaccharides?

Answer 21

-homopolysaccharides are made up of the same monosaccharides
-heteropolysaccharides are made up of different monosaccharides

Question 22

what is cellulose?

Answer 22

-linear chains of glucose joined by beta 1-4 glycosidic bonds
-main component of plant cell walls
-strong bc lots of H bonds form between the straight chain glucose
-forms more complex structures w other polysaccharides

Question 23

describe chitin

Answer 23

-main structural component of exoskeletons of insects, crustaceans, spiders
-present in cell wall of fungi, algae and in capsule of some bacteria
-structurally different from cellulose bc formed from chains of N-acetyl-D-glucosamine
-stronger than cellulose

Question 24

describe starch

Answer 24

-stores energy in plants as food reserve
-forms insoluble granules in cytoplasm
-made of a-amylose and amylopectin

Question 25

describe a-amylose

Answer 25

-linear homopolysaccharide -glucose monomers linked by alpha 1-4 linkages -forms spiral structure (helical conformation) bc bonds are in different places compared to cellulose - this makes it more compact

Question 26

Describe amylopectin

Answer 26

-branched bc of occasional 1-6 linkages -can contain up to million glucose monomers

Question 27

Describe glycogen

Answer 27

-present in all tissue but prevalent in liver and muscle -structurally similar to amylopectin but more branched -degraded to glucose by glycogen phosphorylase and debranching enzyme

Question 28

Describe glycoproteins

Answer 28

short carbohydrate chains covalently linked to serine, threonine or asparagine -often branched -circulating proteins

Question 29

how is glycogen degraded to glucose?

Answer 29

-glycogen phosphorylase removes glucose molecules at end of chains -debranching enzymes act as transferase by removing glucose molecules near branch points and also cleave branch points

Question 30

what are examples of glycoproteins?

Answer 30

-hormones -antibodies -extracellular matrix -enzymes -components of bacterial cell wall

Question 31

What 2 ways can carbohydrate groups in glycoproteins be linked

Answer 31

N-linked glycosylation tends to be quite variable and has important effects on protein folding, activity and cellular location O-linked glycosylation often occurs in clusters on proteins with a protective role ie mucin

Question 32

what are the functions of salivary mucins?

Answer 32

-Have between 2 and 7 sugar units attached -formation of mucus -lubrication -modulation of oral bacteria

Question 33

what are the two forms of salivary mucins?

Answer 33

high or low molecular weight mucins

Question 34

describe glycolipids

Answer 34

-Cerebrosides and gangliosides -present in all eukaryotic cell membranes -involved in intercellular communications -contain the same oligosaccharides as glycoproteins -act as cell recognition factors -important feature of bacterial cell wall - causes strong immune reaction in humans -glycolipids determine blood group

Question 35

GlycoRNA?

Answer 35

Paper published last year describes existence of glycosylated RNA Found on plasma membrane As yet, function unknown

Question 36

describe digestion of carbohydrates

Answer 36

-begins in the mouth -saliva contains a-amylase which hydrolyses alpha 1-4 linkages except outermost bonds -along w chewing, this reduces polysaccharides to oligosaccharides of eight or less monomers -further digested by pancreatic a-amylase and other glycosidases -some bacteria break up complex carbs that body cannot do itself

Question 37

Digestion overview

Answer 37

Question 38

describe the relationship bw carbohydrate intake and oral health

Answer 38

-high carbohydrate intake is linked to oral health (caries, gum disease (diabetes predisposes) -bacteria in mouth that can cause gum disease uses glycoproteins and glycolipids as food source

Answer 39

Question 40

describe Glycocalyx

Answer 40

-The glycoproteins and glycolipids on the cell surface form the glycocalyx -This forms a thick protective barrier -In bacteria, the glycocalyx can form a layer on which bacteria can adhere to objects such as replacement joints and teeth