Carbohydrates and Nucleic Acids

Are there predominantly L or D sugars in nature?

D

What is amylopectin

D glucose is linked by alpha 1-4 glycosidic bonds but also has branches due to alpha 1-6 glycosidic bonds These branches occur every 24-30 glucose unit

What is amylose

D-glucose linked by alpha 1-4 glycosidic bonds - this forms a spiral sure to the bent structure of alpha 1-4 bonds

What is the name of a sugar that has a 6 membered ring

pyranoses

Which is true about naturally occurring monosaccharides? A. The L-isomers predominate. B. The D-isomers predominate. C. Monosaccharides can be grouped according to the number of carbons in the ring of the cyclic structure. D. Monosaccharides undergo intramolecular cyclisation to give different (α or β) anomers

B. The D-isomers predominate. D. Monosaccharides undergo intramolecular cyclisation to give different (α or β) anomers C is wrong because monosaccharides can be grouped due to the number of carbons AND OXYGENS in the ring!

What are the 2 isomeric forms that are produced from the hemiacetal group formation to produce the cyclic molecule

Beta - This is when the hydroxyl group in the molecule is pointing upwards Alpha - This is when the hydroxyl group is pointing downwards

What are the names of enantiomers that are not mirror images

diasteriomers

What bond joins 2 nucleotides together?

phosphodiester linkage

What bond joins the sugar to the phosphate

phosphoester

Where is cellulose found

plant cell walls

Do monosaccharides show stereoisomerism?

yes

What is the empirical formula of a carbohydrate?

(CH2O)n

What are the 2 main types of bonds that join carbohydrates and proteins together

1) O glycosidic linkage - OH group is linked to Ser or Thr by an between an alpha sugar and a protein 2) N glycosidic linkage - CONH2 group linked to Asn on the protein by an between a beta sugar and a protein

How many enantiomers are there on a molecule that has 4 chiral carbons

4- The number of carbon atoms there are on the molecule will determine the number of enantiomers there are

Which bases are joined together and How many H bonds are there

A and T are joined by 2 hydrogen bonds C and G are joined by 3 hydrogen bonds

Define a glycoconjugate

A carbohydrate linked to proteins and lipids

Define a monosaccharide

A carbohydrate that contains 1 monomeric unit

Define an oligosaccharide

A chain of 2-20 monosaccharides

Define a polysaccharide

A chain of more than 20 monosaccharides

What is a disaccharide? and how does it form

A disaccharide is formed when 2 monosaccharides are joined together by a glycosidic bond - this bond forms when the anomeric carbon reacts with an OH group on the 2nd monosaccharide and a water molecule is lost -

What 3 things are nucleotides made up of?

A five-carbon sugar A heterocyclic nitrogenous base Phosphate group(s)

What is a nucleoside

A nucleotide is called a nucleoside if it doesn't contain a phosphate

Which bases are purines

Adenine and Guanine

Give an example for 2 monosaccharides and how you differentiate between them

Aldose - Where the highly oxidised carbon is carbon 1 (the terminal carbon) Ketose - Where the highly oxidised carbon is carbon 2/another middle carbon) (the middle carbon)

Carbohydrates are presented on a membrane surface, either attached to membrane proteins or to lipids. These carbohydrates: A. Are linked to ceramide units via glycosidic bonds to form glycosphingolipids. B. Can comprise diverse oligosaccharide chains linked to ceramide to form gangliosides. C. Can be covalently linked to proteins by formation of peptide bonds to Arg, Ser or Thr. D. Can attach to proteins via hydrogen bonding with polar amino acid side chains, such as those of Ser and Thr. E. Can be linked to proteins via glycosidic bonds to Asn, Ser or Thr. Which two of the above statements are FALSE?

C. Can be covalently linked to proteins by formation of peptide bonds to Arg, Ser or Thr. - serine/threonine cant for peptide (amide bonds) D. Can attach to proteins via hydrogen bonding with polar amino acid side chains, such as those of Ser and Thr. - You cant attach proteins to carbs by hydrogen bonds

What are the 2 main types of polysaccharide?

Homoglycans - homopolysaccharides containing only one type of monosaccharide - glucose predominantly Heteroglycans - heteropolysaccharides containing residues of more than one type of monosaccharide

What bond joins the sugar to the base?

N glycosidic

What are the 2 types of nucleotide?

RNA and DNA

Which carbon will be the carbon on a glucose monomer whos groups attached will decide if it is alpha or beta

The C1 which is the one on the right

How does a cyclic pentose/hexose monosaccharide form?

The aldehyde group will form a bond with the alcohol group in the sugar to form a hemiacetal bond - the hemiacetal bond will then lose a water molecule and form an acetal group - this overall will form a cyclic molecule

How do you work out which enantiomer is D and which is L

You move molecule so the carbon atoms are in a vertical chain with the carboxyl group (with the most highly oxidised carbon) onto the top - this means that the other 2 groups will be on the left and right - the dash will be underneath the plane of the screen and the wedge comes out of the screen towards you (the other 2 groups will be wedged and come towards you) One will be a hydrogen and the other will be a different group (E.g. a hydroxyl group) The D enantiomer will be the sugar that has the hydroxyl group (group that isn't hydrogen) on the right when you have rearranged it into the fisher form The L enantiomer will be one that has the hydroxyl group on the left

Give the name of an aldehyde with 3 carbons, and 4 carbons

aldotriose and aldotetrose,

Polar heads of glycerophospholipids may be: 1) positive 2) negtaive 3) both 4) neutral 5) all

all

If the first sugar that forms the bond is alpha glucose what is the linkage between the 2 sugars?

alpha 1-4 glycosidic

What 2 carbohydrates make up starch

amylose and amylopectin

What linkages are present between glucose monomers in cellulose

b1-4 linkages

If there are alpha 1-4 glycosidic bonds between sugars is the chain bent or straight

bent

If the first sugar that forms the bond is beta glucose what is the linkage between the 2 sugars?

beta 1-4 glycosidic

How do you determine wether a sugar is D or L if there is more than one chiral carbon

by which chiral carbon is furthest away from the aldehyde (or ketone) group - the direction (left or right) that whichever group on THAT carbon atom that isn't the hydrogen atom will determine the nature of the enantiomer

What shape are pentose and hexose monosaccharides

cyclic

Which bases are pyrimidines

cytosine and thymine

What do 2 polynucleotides associate to form

double helix

What is the name of the sugar that has a 5 membered ring

furanoses

Describe the structure of cellulose

glucose joined by b1-4 linkages to form straight unbranched chains that are connected adjacently by hydrogen bonds

What do animals store glucose as

glycogen

What does the branched nature of amylopectin mean

increase the compactness of the structure and this will increase the number of chain ends which means there is faster formation and degradation

Give the name of a ketone with 3 carbons

ketotriose

What is the bond between 2 phosphates

phosphoanhydride

How is glycogen different to starch

similar to amylopectin but larger and is more highly branched - this means it is a more compact structure and a faster metabolism

What do plants store glucose as

starch

If there are beta 1-4 glycosidic bonds between sugars is the chain bent or straight

straight

Which monosaccharides show steroism isomerism

when the carbon atom in the monosaccharide has 4 different groups attached to it (contain an asymmetrical carbon atom)