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CU: Biochemistry > Exam 2 (Not on Final) > Flashcards

Exam 2 (Not on Final) Flashcards

Carbohydrates

1
Q

What are carbohydrates and what are the two groups? What is other nomenclature we need to know?

A

A carbon based molecule with a ton of hydroxyl groups (CH2O)n: typically seen as a carbonyl with a bunch of OH groups
Aldose: has an aldehyde group
Ketose: has a ketose group
Number of C: Tri-, tetr-, pent-, hex-, heptose

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2
Q

What makes a sugar D or L? Which conformation is most natural sugars in?

A

How it relates to D or L-Glyceraldehyde
If the last C OH group is on the right it is D on the left it is L
- Most natural sugars are D

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3
Q

What is a pyranose ring? How does it form? What conformation does it adopt? What are the anomers?

A

A six-membered ring with an O similar to pyran
Forms: open chain C-5 OH attacks C-1 from bottom or top –> a (opposite) and B (same) anomers depending what side the OH on the C-1 relative to C-6 group
- C-1 is an aldehyde making it the anomeric carbon
- Conformation: chair - If there is no C-6 group then if OH on C-1 is axial it is a if equatorial it is B

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4
Q

What is a furanose ring? How does it form? What conformation does it adopt?

A

A five-membered ring with an O looks like furan
still a 6-C open conformation
Forms: C-5 OH attacks C-2 from top or bottom. a (opposite) and B (same) depending on C-2 OH relation to C-6.
- C-2 is the anomeric carbon
- Envelope form: four C in plane one not either 3: C-3-endo or 2: C-2-endo

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5
Q

What is an anomeric carbon atom? What are the types of anomers?

A

Anomeric carbon atom is the one creating the hemiacetal or hemiketal and has the OH that determines if it is a or B

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6
Q

What is the Hawthorne projection?

A

It is the ring projection that has a bold line indicating the bond that goes out toward the viewer.

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7
Q

What is glycolysis?

A

The metabolism of glucose to make 2 net ATP and 2 pyruvate anaerobically

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8
Q

What is a monosaccharide?

A

Simple sugars made of an aldehyde or ketone, two or more hydroxyl groups and 3-7 Carbon atoms. That have isomeric forms.

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9
Q

What are the most common monosaccharides?

A

Dihydroxyacetone (ketose)
D-Glyceraldehyde and L-Glyceraldehyde (aldose)

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10
Q

What are the isomerism seen in carbohydrates?

A

Either constitutional (same molecular formula, different binding) or stereoisomer (same binding different spatial arrangement) which are either enantiomers (nonsuperimposable mirror images) or diastereomers (some but not all stereocenters are flipped) a subset of which are epimers in which only one stereocenter is flipped a subset of with are anomers

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11
Q

What is the classification of fructose?

A

Fructose is a hexose even though it is most stable as a furanose in ring form. (can make pyranose but most stable as furanose)

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12
Q

What happens when sugar aldehydes or ketones react with an alcohol? What makes the sugar special?

A

Aldehyde + alcohol = hemiacetal (free OH, OR’, R, H) (+ microscopic amount acid/base)
Ketone + alcohol = hemiketal (free OH, OR”, R, R’)
Sugars unique because make hemi form not full form because they make happy 5-member and 6-member rings

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13
Q

What structures and names should we memorize?

A

B-D-Ribofuranose, B-2-Deoxy-D-Ribofuranose, a-D-Glucopyranose, a-D-Fructofuranose, a-D-Galactopyranose

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14
Q

What is the structure of B-D-Ribofuranose?

A

C-1 (U:OH, D:H)
C-2 (U:H, D:OH)
C-3 (U:H, D:OH)
C-4 (U:CH2OH, D:H)
O

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15
Q

What is the structure of B-2-Deoxy-D-Ribofuranose?

A

C-1 (U:OH, D:H)
C-2 (U:H, D:H)
C-3 (U:H, D:OH)
C-4 (U: CH2OH, D:H)
O

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16
Q

What is the structure of a-D-glucopyranose?

A

C-1 (U:H, D:OH)
C-2 (U:H, D:OH)
C-3 (U:OH, D:H)
C-4 (U:H, D:OH)
C-5 (U: CH2OH, D:H)
O

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17
Q

What is the structure of a-D-fructofuranose?

A

C-2 (U:CH2OH, D:OH)
C-3 (U:OH, D:H)
C-4 (U:H, D:OH)
C-5 (U:CH2OH, D:H)
O

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18
Q

What is the structure of a-D-Galactopyranose?

A

C-1 (U:H, D:OH)
C-2 (U:H, D:OH)
C-3 (U:OH, DH)
C-4 (U:OH, D:H)
C-5 (U:CH2OH, D:H)
O

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19
Q

What is “blood sugar”? Function? Importance? What do the evolutionists think? Other reactivity facts?

A

D-glucose, what the brain needs and is RBC fuel, Proper levels are very important
Evolutionists: Formed from formaldehyde in prebiotic conditions
- Relatively inert and most stable ring as B
- Two anomeric forms (a and B) are in equilibrium through the open chain form
- Since B is more stable will be 2:1 with a in equilibrium

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20
Q

What do glycosidic bonds do? What are the three most common reactants?

A

increase the biochemical versatility of carbohydrates
- signal molecules
- facilitating metabolism
Most common reactants: alcohols, amines, and phosphates

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21
Q

What are the two types of glycosidic bonds? What are the differences between them?

A

O-glycosidic: bonds anomeric carbon with O of an alcohol
*Links monosaccharides into di/polysaccharides
N-glycosidic: bonds anomeric carbon with N of amine

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22
Q

What are the aspects of sucrose? (Monosaccharides, linkage, enzyme)

A

(common table sugar)
- a-glucose & B-fructose
- glycosidic linkage between anomeric carbons (C-1, C-2): a-1-2-linkage
- enzyme: sucrase

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23
Q

What are the aspects of lactose? (Monosaccharides, linkage, enzyme)

A

(in milk)
- galactose & glucose
- B-1-4-linkage
- lactase

24
Q

What are the aspects of maltose? (Monosaccharides, linkage, enzyme)

A

(from starch)
- two glucoses
- a-1-4-linkage
- maltase

25
Q

What does cellulose consist of?

A

(plant cell walls) - structure
- glucose with unbranched B-1-4-linkages –> long straight and strong chains
(important to animal digestion to speed up digestion –> less exposure to toxins)

26
Q

What does glycogen and starch consist of? What is their structure/function? What is the difference between these two?

A

a linkages of glucose –> open helices for mobilizable energy stores of glucose to not disrupt osmotic balance
- Glycogen: large, branched with mostly a-1-4 linkages but a-1-6 linkages ~ every 10 (animals)
- Starch: amylose - unbranched a-1-4-linkages and amylopectin with a-1-6-linkages about every 30 a-1-4-
(increased branching of glycogen make it easier to metabolize)

27
Q

What makes a sugar a reducing or non-reducing sugar? What happens?

A
  • If the sugar can get to its open chain form freeing up a carbonyl it will be a reducing sugar
  • it turns into its acid/carboxylate form
  • the sugar is being oxidized so it is a reducing agent
28
Q

What tests for sugars?

A

Fehling’s solution: solutions of cupric ion
- if react = reducing sugar

29
Q

What does too much reducing sugar cause in the body?

A

Often react with free amino groups forming a stabile covalent bond (glucose: glycosylated - hemoglobin tests for diabetes no functional effect - other glycosylation detrimental b/c effect function ie modifications implications in aging: Advanced glycation end products (AGE) (aging, arteriosclerosis, diabetes, other pathological conditions)

30
Q

What are the most common groups added to modify carbohydrates? Where do they attach?

A

Attach at places other than anomeric carbon
Common substituents:
- Methyl (CH3)
- amide (HN-C(-O)-CH3) (as in GalNAc and GlcNAc)

31
Q

What is phosphorylation predominant in? What are the three common intermediates? What does it do?

A
  • Predominant in metabolism (esp glycolysis)
  • Intermediates: G-6P, DHAP, GAP
  • Function: makes sugars anionic
    – prevent lipid bilayer crossing
    – prevent interaction with transporters of unmodified sugar
32
Q

How does one tell oligosaccharide directionality?

A

The reducing and non-reducing end
Only the anomeric position (C b/w two O) can reduce
- Question: Does the anomeric carbon have an OH? (reducing) or an OR? (non-reducing)

33
Q

What is a glycoprotein? What is their prevalence in the proteome? Why might this occur? What is the effect?

A
  • carbohydrate covalently attached to a protein (any protein w/ a sugar attached)
  • Prevalence: 50%
  • May occur because protein has many glycosylation sites
  • Effect: increases protein complexity
34
Q

What are the three classes of glycoproteins and what are the major differences? (composition, functions)

A

1) Glycoproteins:
- composition: more protein
- functions: cell adhesion, glycosylation to make proteins insoluble
2) Proteoglycans:
- composition: glycosaminoglycan (95%), more carbohydrate,
- function: structure & lubrication & adhesion to ECM, regulate cell proliferation
3) Mucins/mucoproteins:
- composition: more carbohydrate (usually N-Acetylglucosamine, an amino sugar)
- function: mucus lubricant

35
Q

What are glycoforms?

A

Proteins glycosylated at different locations having different forms

36
Q

What is an amino sugar?

A

An amino replaces a hydroxyl group on a sugar.

37
Q

What are the two ways sugars are attached to proteins? (Three things about first one)

A

N-linkage: amide N atom in Asn
- ONLY if: Asn-X-Ser or Asn-X-Thr and X is anything but Pro
- ALL: pentasaccharide core–3 mannose & 2 N-acetylglucosamine (GlcNAc)
- Variety: comes from additional sugars attached to core
O-linkage: O in Ser or Thr

38
Q

Are all potential protein sites glycosylated? Why/why not?

A

No, it depends on protein structure and cell type

39
Q

What is erythropoietin an example of?

A

glycoprotein present in the blood in which glycosylation increases stability and bioactivity
(Has three N-glycosylated & one O-glycosylated)

40
Q

What is the attachment of GlcNAc to Ser or Thr of cellular proteins? What is important about the sites?

A

GlcNAcylation
Especially important glycosylation reaction, reversible
- covalent attachment
- catalyzed by GlcNAc transferase
- sites: also potential phosphorylation –> O-GlcNAc transferase & protein kinases may cross talk to modify signaling activity
(Dysregulation GlcNAc transferase –> pathologies)

41
Q

What does the concentration of GlcNAc indicate?

A

active metabolism of carbohydrates, amino acids, and fats (nutrients are abundant: nutrient sensing)

42
Q

What are glycosaminoglycans made of? What must be present? What are the major glycosaminoglycans?

A

many made of repeating disaccharides w/ derivative of amino sugar: glucosamine or galactosamine
- at least one of two sugars has negatively charged carboxylate or sulfate group
Major: dermatan/chondroitin/keratan sulfate, heparin, and hyaluronate
(Inability to degrade–> mucopolysaccharidoses)

43
Q

What is cartilage an example of?

A

proteoglycan- carb- aggregate & protein- collagen
Protein: 3 globular domains & site of glycosaminoglycan attachment b/w domain 2 & 3 for keratan & chondroitin sulfate. ++ aggrecan bounded to globular 1, shock absorber b/c water bound to hyaluronate attracted by sugar hydroxyl groups
(OA: when water go out & cannot go back in)

44
Q

What is the defining feature of mucins? What do mucins do?

A

variable number of tandem repeats: VNTR a protein backbone rich in O-glycosylated Ser and Thr & N-acetylglucosamine very important
- Function: adhere to epithelial cells & protect/hydrate cells also fertilization, immunity, cell adhesion

45
Q

Where does protein glycosylation occur?

A

Protein synthesized on cytoplasmic face ER –> ER lumen
N-linked glycosylation begins in ER & continues in Golgi
O-linked glycosylation ONLY Golgi

46
Q

What is dolichol phosphate?

A

specialized lipid molecule in ER membrane w/ ~20 isoprene units and a terminal phosphate group

47
Q

What else does the Golgi do?

A

Golgi alters & elaborates carbohydrate units of glycoproteins and is the major cell sorting center –> Lysosomes/secretory granules/plasma membranes

48
Q

How are complex carbohydrates formed?

A

Glycosyltransferases: catalyzing glycosidic bonds
- Most common carbohydrate donors: activated sugar nucleotides ie UDP-glucose
- Acceptor substrates varied, including carbohydrates, Ser, Thr, Asn residues of proteins, lipids, nucleic acids

49
Q

What are blood groups an example of?

A

Glycosyltransferases effecting glycoproteins
ABO all have common O antigen
Type A transferase adds N-acetylgalactosamine
Type B transferase adds galactose

50
Q

What do glycosylation errors cause?

A

pathological conditions due to proteins not going where they were supposed to go

51
Q

How are oligosaccharides sequenced?

A

oligosaccharides can be blown apart and sequenced using mass spectroscopy also can be analyzed by MALDI-TOF

52
Q

What are Lectins?

A

A specific class of glycan-binding proteins that bind specific carbohydrate structures on neighboring cell surfaces
- Usually has two or more carbohydrate binding sites
(illustrate how carbohydrates are information-rich molecules that guide many biological processes)

53
Q

What do lectins do?

A

Facilitate cell-cell contact
- noncovalently interacting with the carbohydrates on another cell surface

53
Q

What are the types of lectin classes? How are the classes made? Function examples?

A

Basis: amino acid sequence and biochemical properties
C type: (calcium requiring) in animals. Calcium ion is a bridge between protein and sugar + 2 Gln
Functions: include receptor-mediated endocytosis
L type: legumes
- Functions: insecticides, chaperones in eukaryotic ER

53
Q

What are selectins?

A

C-type lectins involved in the immune system.
Certain kinds bind to carbohydrates in
L) lymph-node vessels (also produced by embryo to attach to mother)
E) endothelium
P) activated blood platelets

53
Q

What is the influenza virus an example of? What does it do?

A

Uses hemagglutinin (another name for lectins) to bind to sialic acid residues linked to galactose residues on the cell surface glycoproteins to get into the cell to replicate then to exit virus buds attached to sialic acid by hemagglutinin and the viral protein neuraminidase cleaves glycosidic bonds b/w sialic acid residues and rest of cellular glycoprotein

CU: Biochemistry (4 decks)

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