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Biochemistry 441B > Carbohydrate Structure & Function > Flashcards

Carbohydrate Structure & Function Flashcards

1
Q

What are three types of carbohydrates?

A

Simple sugars
Polysaccharides
Glycoconjugates

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2
Q

What is another name for carbohydrates?

A

Glycans

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3
Q

What are glycans?

A

Polyhydroxy aldehydes or ketones or substances that yield such compounds on hydrolysis

Very heterogeneous in size and composition

Named so because many have formula Cn(H2O)n, where n ≥ 3

Glycans = Carbohydrates

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4
Q

What is the most abundant biological molecules and how are they produced?

A

Glycans (Carbohydrates)

Produced from CO2 and H2O via photosynthesis in plants

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5
Q

What can carbohydrates covalently link to?

A

Proteins and lipids

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6
Q

What functions do carbohydrates fulfill?

A

Energy source and energy storage

Structural component of cell walls and exoskeletons

Informational molecules in cell-cell signaling

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6
Q

What are examples of simple sugars?

A

Monosaccharides
- glucose, galactose, mannose

Disaccharides
- sucrose, maltose, lactose

Oligosaccharides
- milk oligosaccharides, raffinose

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6
Q

What are examples of polysaccharides?

A

Glucose homopolymers
- cellulose, starch, glycogen

Disaccharide heteropolymers
- keratan, sulfate

Chitin is a homopolymer of N-acetyl glucosamine

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6
Q

What are examples of glycoconjugates?

A

Glycoproteins
- antibodies, viral coat proteins

Proteoglycans
- aggrecan, syndecan, glypican

Glycolipids
- blood antigens, membrane anchors

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7
Q

What are oligosaccharides?

A

Simple sugars that range from 3-20 unbranched and branched sugar residues

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8
Q

What are milk oligosaccharides?

A

They are derived from lactose

Lacto-N-tetrarose
Lacto-N-fucopenraose-1

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9
Q

What is the importance of human milk oligosaccharides?

A

Important functions in the infant intestinal tract

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10
Q

What does Lacto-N-tetrarose do in the infant intestinal tract?

A

Helps with digestion

Growth advantage to bifidobacteria

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11
Q

What does Lacto-N-fucopentaose 1 do in the infant intestinal tract?

A

Fools bacteria with itself so it binds to the carbohydrate instead of the receptor of the cell

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12
Q

What are examples of plant oligosaccharides?

A

Raffinose
Stachyose
Verbascose

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13
Q

What are plant oligosaccharides derived from?

A

Sucrose

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14
Q

Why can humans and non-ruminating animals (pigs, poultry) not digest plant oligosaccharides?

A

Humans and non-ruminating animals lack the a-galactosidase enzyme needed to hydrolyze the a-1,6 glycosidic bond.

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15
Q

What is beano?

A

A preparation of a-galactosidase that can aid in digestion of plant oligosaccharides, resulting in the release of free galactose and sucrose

Sucrose is further metabolized to glucose and fructose by the enzyme sucrase in the small intestine

These simple sugars are easily metabolized by our own enzymes

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16
Q

What are the types of polysaccharides?

A

Homopolysaccharides

Heteropolysaccharides

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17
Q

What are homopolysaccharides?

A

They can be unbranched (linear) and branched (every now and then)

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18
Q

What are heteropolysaccharides?

A

They can be unbranched with two monomer types and branched with multiple monomer types.

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19
Q

What do polysaccharides not have?

A

They do not have a defined molecular weight and composition

This is in contrast to proteins because unlike proteins, no template is used to make polysaccharides

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20
Q

What are the functions of polysaccharides?

A

Some serve as structural elements

Some serve as storage forms of monosaccharides that are used as fuels

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21
Q

What are examples of structural polysaccharides?

A

Cellulose (plant cell walls)

Chitin (animal exoskeletons)

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22
What are examples of storage polysaccharides?
Starch in plants Glycogen in animals
23
What is cellulose?
An unbranched homopolysaccharide consisting of ~1000 repeating units of a disaccharide cellobiose
24
What is cellobiose?
2 glucose (Glc) monomers linked by (B1-->4) glycosidic bonds
25
What bonds does cellulose have and where?
H-bonds between cellulose strands
26
What is cellulose a component of?
Component of the plant cell wall
27
What is the most abundant polysaccharide in nature?
Cellulose
28
What is nearly pure fibrous cellulose?
Cotton
29
Why are individual cellulose strands extensively hydrogen-bonded?
To build a polysaccharide fibril
30
What do most animals lack in terms of polysaccharides?
Most lack cellulase
31
What is cellulase?
The enzye required to hydrolyze the B1-->4 linkage between glucose molecules in cellulose
32
What is high in cellulose?
Plant material
33
What is plant material high in cellulose considered?
Considered "roughage in the diet" | - it passes through the digestive system without being degraded
34
What can fungi, bacteria, and protozoa do in terms of cellulose?
Secrete cellulase, that can use wood as source of glucose
35
What do ruminants and termites have in relation to cellulose?
They live symbiotically with microorganisms that produce cellulase
36
What is chitin?
Linear homopolysaccharide of N-acetyl Glucosamine (GlcNAc) units - Contains B1-->4 glycosidic bonds Structural exoskeletons in insects and crustaceans Also found in cell walls of many types of fungi, including mushrooms
37
What does chitin provide?
Provides a strong body frame
38
What bonds does chitin have and where?
H-bonding within and between polysaccharide strands
39
What is starch?
The main storage polysaccharide in plants
40
What are the two forms of starch that plants synthesize?
Amylose Amylopectin
41
What is amylose?
an unbranched (linear) polymer of ~100 (a1-->4) linked glucose units humans can metabolize this called amylase to break it down
42
What is amylopectin?
a (a1-->4) linked glc polymer with (a1-->6) branching occuring every 15-30 residues linear chain with branches - homopolymers Left handed
43
How is starch different from cellulose and chitin?
Starch is an important dietary source of glucose for animals
44
Why is starch an important dietary source of glucose for animals?
It can be hydrolyzed by the enzyme a-amylase which cleaves (a1-->4) glycosidic bonds
45
What is glycogen?
Branched homopolysaccharide of glucose - just like amylopectin but is more heavily branched Molecular weight reaches several millions Glycogen bonded to only 1 glucose
46
In glycogen, what do glucose monomers form?
(a1-->4) linked linear chains
47
In glyocogen, describe its branch points.
(a1-->6) linkers every 8-12 residues
48
What is the main function of glycogen?
Main storage polysaccharide in animals
49
Where is there an abundance of glycogen?
Abundant in liver (~7-10% wet weight of liver) and in skeletal muscles
50
What does glycogen and starch often form?
Granules in cells
51
What do granules contain?
Enzymes that synthesize and degrade these polymers
52
What do glycogen and amylopectin have?
One reducing end but many non-reducing ends Anomeric carbon has to attack at the non reducing end
53
Where do enzymatic processing occur?
Occurs simultaneously at many non-reducing ends Therefore, more branch points provide more ends for Glc retrieval and storage
54
What is the advantage of storing glucose as starch or glycogen?
Greatly reduces osmotic pressure that would result from its storage in monomeric form This is because osmotic pressure is proportional to the number of solute molecules (regardless of their given weight) in a given volume.
55
What are important roles does glycans have?
In addition to the energy and structural roles, it has an important role as functional groups in glycoconjugates
56
How much of all human proteins are glycoproteins?
~50%
57
How much of the human genome encodes enzymes required for the synthesis and degradation of carbohydrates and glycojungates?
~1%
58
What enzymes are required for the synthesis and degradation of carbohydrates and glycoconjugates?
Glycosyltransferases Glycosidases
59
What are glycosyltransferases?
Covalently linked glycans to proteins and lipids
60
What are glycosidases?
Remove glycans through hydrolysis reactions
61
What are the types of glycoconjugates?
Glycoproteins Proteoglycans Glycolipids
62
What are glycoproteins?
Bulk of the macromolecule consists of protein - Some are transported by membrane vesicles to the plasma membrane for insertion or secretion - Others are targeted to cellular organelles such as mitochondria, peroxisomes
63
What are proteoglycans?
Bulk of the macromolecule consists of carbohydrates
64
In humans, where are proteoglycans found?
Extracellular matrix
65
In bacteria, where are proteoglycans found?
Cell wall (peptidoglycans)
66
Where are glycoproteins transported?
transported to the plasma membrane for insertion or secretion by membrane vesicles
67
What targets glycoproteins?
Cellular organelles such as mitochondria, peroxisomes target some glycoproteins (the other half that i'snt transported)
68
Glycan groups on glycoconjugates are recognize by glycan binding proteins called ______.
Lectins
69
What are lectins?
Special class of proteins Glycan group-lectin interactions play important role in cell signaling and immunity
70
What are colored symbols for monosaccharides used as?
Used as building blocks of the glycan groups in most glycoconjugates Simplifies representation of the glycan group of the glycoconjugate Consortium for Functional Glycomics (CFG) notation
71
Where on the protein do the glycans attach?
N- and O-Linked glycosylation N-Linked = Asn always (GlcNac) O-Linked = Ser or Thr (GalNAc)
75
What is N-Linked Glycosylation?
Carbohydrate linkage occurs through the amide N atom in the side chain of Asn.
76
What does N-glycosylating enzymes most often attach to?
Often attach the sugar to asparagine (Asn) residues contained within the consensus sequence Asn-X-Ser/Thr (X can be any amino acid except Pro)
77
What is the consensus sequence?
Asn-X-Ser/Thr (X can be any amino acid except Pro) Matters how it is attached
78
What is O-Linked Glycosylation?
Carbohydrate linkage occurs through the O atom in the side chain of Ser or Thr residues
79
What is the consensus sequence for O-glycosylating enzymes?
Unlike N-glycosylating enzymes, the O-glycosylating enzymes do not have a preferred consensus sequence TLDR: O-glycosylating enzymes does not have a consensus sequence
80
What are mucins?
O-linked glycoproteins are often called mucins Mucins function to protect epithelial cells in the intestinal, urinary and respiratory tracts from physical damage and pathogens
81
Which enzymes determine the expression of human ABO blood groups?
a-1,3-N-acetylgalactosaminyltransferase (GTA) a-1,3-galactosyltransferase (GTB) These enzymes attach either a GalNAc (GTA) or Gal (GTB) sugar residue to a glycan subgroup called the O antigen
82
If neither GTA or GTB enzymes are present, which blood type group is it?
O-type blood
83
If only GTA enzyme is present, which blood type group is it?
A-type blood Adds square (GalNAc)
84
If only GTB enzyme is present, which blood type group is it?
B-type blood Adds circle (Gal)
85
If both GTA and GTB enzymes are present, which blood type group is it?
AB-type blood Adds square and circle (GalNAc, Gal)
86
What is the O antigen?
Glycan subgroup where a-1,3-N-acetylgalactosaminyltransferase (GTA) and a-1,3-galactosyltransferase (GTB) attach to either a GalNAc (GTA) or Gal (GTB) sugar residue
87
Where is the O antigen present?
Present on glycoproteins and glycolipids on red blood cells
88
Which blood group is a universal red blood cell acceptor?
Type AB blood
89
Which blood group is a universal red blood cell donor?
Type O blood
90
Which blood group is a universal plasma acceptor?
Type O blood
91
Which blood group is a universal plasma donor?
Type AB blood
92
What happens if anti-A and anti-B antibodies meet anti-O antibodies?
They will attack each other
93
What are proteoglycans?
Proteins with multiple long glycosaminoglycan chains covalently attached to a relatively small core protein Attached to a hyaluronic acid through a linker protein Extracellular matrix proteoglycans and cell surface proteoglycans
94
Where do proteoglycans function?
Membrane-bound through a Glyco-phosphatidyl inositol (GPI) anchor or a transmembrane a helix on the protein Secreted into the extracellular matrix (most function here)
95
What is a peptidoglycan?
Component of bacterial cell wall Provides shape and protection against osmotic changes - Linear chains of B(1-->4) linked MurNAc and GlcNAc tethered together by linkages between short peptides ``` MurNAc = N-Acetylmuramic acid GlcNAc = N-acetylglucosamine meso-DAP = Meso-diaminopimelic acid (derivative of lysozyme) ```
96
What does lysozyme do in a peptidoglycan?
Breaks B(1-->4) bond which can neutralize bacteria
97
What does penicillin do?
Blocks bacterial cell wall synthesis by inhibiting Transpeptidase When transpeptidase is inactive, cell wall synthesis is inhibited and bacterial cells die. Forms a suicide inhibitor complex between a Ser residue in transpeptidase and a carbonyl C in the B-lactam ring of penicillin
98
What is transpeptidase required for?
This enzyme is required to form the oligopeptide linkages between polysaccharide chains (gives it strength)
99
Why is penicillin considered a "suicide inhibitor"?
A suicide inhibitor is one that inhibits an enzyme and the mechanism of inhibition such that no conditions exist by which this inhibition can be overcome in the cell. Penicillin forms an irreversible, covalent bond with transpeptidase. The presence of this bond inactivates the enzyme and the irreversible nature of the bond makes penicillin a suicide inhibitor.
100
How has bacteria developed mechanisms to resist B-lactam antibiotics?
Penicillin-resistant bacteria express the enzyme B-lactamase, which inactivates penicillin by cleaving the B-lactam ring
101
What is the solution to bacteria with resistance to B-lactam antibiotics?
Synthetic compounds that block Transpeptidase activity without being a substrate for B-lactamase such as Methicillin
102
What new problem arose after the use of methicillin?
Methicillin-resistant S. aureus (MRSA) bacterial strains arose that express a variant form of the transpeptidase enzyme that is not inhibited by the antibiotic This variant transpeptidase has no reaction with methicillin which allows transpeptidase to be active and allowing bacterial cells to live

Biochemistry 441B (10 decks)

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