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Biochemistry > Carbohydrates > Flashcards

Carbohydrates Flashcards

1
Q

monosaccharides

A

1 sugar unit

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2
Q

disaccharides

A

2 sugar units covalently linked

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3
Q

oligosaccharides

A

several sugar units

  • most important are the ones attached to proteins or lipids outside of the cell
  • important in cell- cell interactions in the nervous system
  • brain
  • coat blood cells and determine blood group
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4
Q

polysaccharides

A

long chains of 100s-1000s

  • linked by glycosidic bonds
  • a(1-4) or B(1-4)
  • can be straight or branches
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5
Q

What are carbs involved in?

A
  1. Energy transport and storage (glycogen)
    * glucose gets broken down to release energy
  2. Structural
    * bacterial cell walls, cellulose and peptidoglycan
  3. Information
    * signals on proteins and membranes
    * blood group antigens- when transfusing you have to be careful because if they have type A you cant give type B or type AB because carbos on the surface of red blood cells wont match, causes immune response which isnt favourbale
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6
Q

What are the 2 major carb families?

A
  1. Aldoses- carbonyl is always on c1
    * derive from D- glyceraldehyde
  2. Ketoses- carbonyl is always on C2
    * derive from dihydroxyacetone

BOTH have asymmetric chiral carbons
EXCEPT FOR dihydroxyacetone

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7
Q

glucose

A

Glc

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8
Q

glucosamine

A

GlcN
amino sugar
- sugar derivative

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9
Q

Fructose

A

Fru

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10
Q

Galactose

A

Gal

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11
Q

Galactosamine

A

GalN

  • amino sugar
  • sugar derivative
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12
Q

N-Acetylglucosamine

A

GlcNac

  • sugar amide
  • sugar derivative
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13
Q

Ribose

A

Rib

  • deoxy- sugar
  • sugar derivative
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14
Q

Why do ketohexoses have 1 less chiral centre

A

because of symmetry carbonyl group will go down into molecule will change overall structure because of position

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15
Q

How are most sugars found?

A

As D and most amino acids are in L

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16
Q

How do you identify if a molecule is D?

A

Look at the chiral carbon furthest from the carbonyl and if it has OH on the right its D

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17
Q

What are enantiomers?

A

non super imposable mirror images

  • one is D and one is L
  • if you were to mirror each of the groups are aligned but if you put them on top of each other the groups wouldn’t match
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18
Q

What are diastereomers?

A

non mirror image stereoisomers

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19
Q

Epimers

A

diastereomers that differ in position of only one carbon

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20
Q

What is the epimeric carbon?

A

the carbon that differs between molecules

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21
Q

How do carbs exist in solution?

A

cyclic form

- carbonyl groups react with alchols

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22
Q

Why do some carbs exist as cyclic and not others?

A

the main restriction is steric- small rings (4 or fewer atoms in the ring) are unstable so they don’t have the flex to form cyclic
* have carbonyl group thats an electrophile Oh thats a nucleophile but dont have the ability to form cyclic without straining themselves

A carbon thats 5 or 6 atoms in backbone are most stable when they have formed cyclic structure because they don’t have issues with steric strain and the reactions create an additional chiral centre
formation of cyclic forms is reversible- molecules can shift between linear and cyclic according to stability in solution

23
Q

anomers

A

isomers that differ only at the hemiacetal or hemiketal C and the C is called the anomeric carbon

24
Q

mutarotation

A

the alpha anomer and beta anomer can interconvert through trace amounts of the non-cyclic form
- measured by rotation of plane- polarized light
- pure alpha glucose rotates light at 112
- pure B rotates at 19
at equ the mixture rotates light +53- weighted average (beta is more prevalant)

25
Q

Equitorial

A

group in plane with planar part of ring, less steric hinderance for bulky groups(best for bulky groups, want as many as them in this position as possible)

26
Q

axial

A

group perpendicular to planar part of the ring

27
Q

sugar derivatives

A

K

28
Q

What can glucose form?

A

It can form 2 cyclic structures involving 6- membered ring

they are different because the new chiral centre can be alpha or beta

6 membered ring is preferred over the less stable 5 membered ring
* structure is called pyranose

29
Q

B- anomer

A

OH on the C1 is on the same side of the ring as c6

30
Q

a- anomer

A

OH on the c1 is on the opposite to C6

31
Q

Describe cyclic ketoses

A

the rings are puckered

  • different positions they take on for stability
  • have groups in positions that will provide greatest stability and lowest delta G
32
Q

Furanose

A

5 membered ring structures

*called this because of their resemblance to furan

33
Q

maltose

A
  • reducing sugar made from starch and amylase

- Glc (a1-4) Glc

34
Q

isomaltose

A
  • Glc (a1-6) Glc
  • a reducing sugar made from hydrolysis of dextrans
  • hydrolyzing a branched sugar
35
Q

Cellobiose

A
  • Glc (beta 1-4) Glc

- a reducing sugar produced by acid hydrolysis of cellulose

36
Q

Are humans able to breakdown cellulose?

A

No we are not able to hydrolyze cellulose because we do not have the enzymes to break beta bonds

37
Q

Lactose

A

Gal (beta 1-4) Glc

  • reducing sugar (able to mutarotate, linearize, donate electrons)
  • major sugar of milk
38
Q

Sucrose

A
  • Glc (alpha 1-B2) Fru
  • non reducing sugar made by plants- table sugar
  • formed by reacting the anomeric carbons so no hemiacetal or ketal function
  • doesnt undergo mutarotation
39
Q

What happens when sucrose is hydrolyzed?

A

When hydrolyzed with acid to Glc + Fru an effect called inversion of sucrose happens- 1:1

  • sucrose rotates light by +66
  • hydrolysis gives a 1:1 mixture of D-Glu (a=+52) and D Fru (a=-92) which rotates light with a=-39
  • mixture is called “invert sugar” because of change of sign
40
Q

Trehalose

A
  • Glc (alpha 1-a1) Glc consists of 2 Glc units linked together through their anomeric carbon
  • non reducing
  • cant mutarotate
  • used for energy storage in insects
41
Q

Why are oligosaccharides on the outside of cells?

A

Want them to be on the outside so immune system can recognize and if it doesn’t then it can mount a response against blood group and cause rejection

42
Q

What are the important roles of polysaccharides in biology?

A
  1. Storage of sugar units (compact (polymeraize or depolymearize easily) Units cane be easily added or removed by enzymes as needed
    glycogen, starch
  2. Structural
    - tough molecules, resistant to degradation by enzymes, fold up into organized structures to maintain cell walls
    * peptidoglycan, chitin- help resist osmotic rupture
43
Q

Why don’t we store sugar as free glucose, why do we make glycogen?

A

Non polymerized glc= osmotically active

- if we pack a bunch of it into the cell water rushes in and it will burst and kill you

44
Q

Starch

A

the storage form of D-Glc in plants

- 2 types: amylose and amylopectin

45
Q

Amylose

A
  • unbranched chains of a(1-4) linked glc units up to 4,000 per chain
  • form a helix(NOT SAME AS SECONDARY STRUCTURE IN PROTEIN)
46
Q

Amylopectin

A
  • up to 200 amylose chains linked by a(1-6) branches

- cant form a helix

47
Q

Why can amylopectin not form a helix?

A
  • because to large and bulky to much rigidity
48
Q

Glycogen

A

animal cell storage of Glc

  • similar to amylopectin but more branched- 15-30 sugars/branch
  • stored in liver and muscle only
49
Q

Dextrans

A
  • bacterial polysaccharides with a(1-6) links and some a(1-2) and A(1-4) links
  • incomplete hydrolysis of starch and glycogen gives some disaccharide
  • can be broken down by disaccharides
  • most of it is maltose linked coming from the straight portions of the polysaccharide plus some isomaltose come from branches
50
Q

Explain why glycogen is stored only in the liver and muscle

A
  • because its not effective storage
  • better to store energy as fats because you get 2X the amount of energy
  • we store in the liver because its fast (easy to access in times of need)
51
Q

In the intestine how do you absorb sugar

A

ALL sugar must be monosaccharides because we don’t have the means to bring in

52
Q

Cellulose

A
  • linear chains of 10-15,000 glucose units linked as in D-cellobiose
  • strong rod like structure of parallel chains packed side by side (for strength and rigidity)
  • fibrous structure is used for textiles(cotton, linen) industrial fibre and paper
    cant be digested by humans but cows have an extra stomach (extra pocket inside tract) and secrete cellulase, an enzyme that cleaves B1-4 glycosidic bonds to release glucose
    *cows are herbivores so form this symbiotic relationship
53
Q

peptidoglycan

A
  • exclusive to bacteria
  • alternating beta 1-4 linked GlcNac and MurNac sugars that are short peptides
  • forms a 3 dimensional mesh like cell wall structure that provides rigidity to the bacteria and protects it from osmotic rupture
  • peptide crosslinks(create perpendicular reinforcements to provide strength and prevent osmotic rupture
54
Q

Lysozyme

A

-degrade bacterial cell walls by catalyzing the hydrolysis of Beta 1-4 linkages(linear linkage) between Nam and Nag

-part of the non specific host defense system
-found in secretions such as tears saliva milk and mucus
found in egg white

Biochemistry (4 decks)

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