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Cell Bio > Glycobiology > Flashcards

Glycobiology Flashcards

1
Q

What are the three main components of glycobiology

A

Lectins Glycans and Glycoenzyems

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2
Q

What are glycans

A

Carbohydrates and sugars

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3
Q

What are lectins

A

Glycan binding protiens

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4
Q

What are glycan modifying enzymes

A

Glycotransferase and glycosidases

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5
Q

What are the central molecules of glycobiology

A

Glycans that are produced or modified by glycoenzymes and recognized by lectins

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6
Q

What is glycocalyx

A

Used to describe the carbohydrate rich zone on the cell surface

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7
Q

How can you recognize the glycocalyx zone

A

Using a variety of stains such as ruthenium red
Also its affinity for carbohydrate-binding protiens called lectins which can be labeled with a flourescent dye or another visible marker

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8
Q

What is glycocalyx made up of

A

Glycan chains of membrane glycoproteins and glycolipids and absorbed glycomolecules

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9
Q

What is the function of the glycocalyx

A

Protect cells against mechanical and chemic to keep foreign objects and other cells at a distance preventing undesirable protien-protein interacations

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10
Q

What else can membrane glycoproteins do

A

Involved in transmembrane signalling and intercellular communications

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11
Q

What does the glycocalyx represent

A

Glycans represent complex branched structures of different sizes that looks like trees

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12
Q

What does the different dimensions of the glycocalyx mean

A

That the role of the glycocalyx may be cell-speceific and be involved in regulation of different cellular responses

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13
Q

How many common monosaccharides are there

A

9

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14
Q

D-glucose can exist in how many forms and what are they

A

three different forms a linear and two different rings a pyranose and furanose

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15
Q

Which ring of D-glucose dominantes in biological systems

A

Pyranose

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16
Q

What are the two different forms of anomers

A

Anomers and steriosmers which include alpha and beta anomers depending on the positon of the hydroxol group at position one

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17
Q

What is it called when sugars differ only by the configuration around one carbon atom

A

Epimers D-manose and Dglacotse are epimers of D-glucose

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18
Q

What are protiens

A

Linear polymers containg up to several thousand amino acids linked by peptide bonds

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19
Q

What are nucleic acids

A

Linear polymers containt hundreds to millions of nucleotides by phosphodiester bonds

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20
Q

What are glycans

A

Linear or branched polymers or monsaccharides linked by glycosidic bonds

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21
Q

What is the glycosidic bond formed by

A

The anomeric carbon of one monosaccharide and a hydroxyl group of another

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22
Q

What is the difference between glycans and proteins and nucleic acids

A

The glycosidic bonds can be formed between individual monsaccharides

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23
Q

What is an example of different bonds between individual monosaccharides

A

Lactose has a different bond between glactose and glucose then glucose has with fructose as result complex branched structures are common

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24
Q

What is the linkage in N-linked glycans

A

GlcNAc B linked to the amide nitrogen of an asparagine residue in the seqeuce Asn-X-Ser or Asn-X-Thr where X is any amino acid expect proline or aspartic acid

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25
Q

What is the first sugar of N-glycans attached

A

GlcNac

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26
Q

What is the linkage of glycans in O-linked

A

Attached to the OH group of either serine or theroine resuidues

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27
Q

What is the most common O-glycosidic attachment

A

Involves the disaccharide core B-glactosyl (1-3) a- N-acetylglactoasimne

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28
Q

What are less common O-linked glycans

A

Glactose, mannose and xylose

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29
Q

Can O-linked glycans vary in size

A

YES from a single sugar residue to the long chains of up to 1000 monosaccharides units in proteoglycans

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30
Q

What do all N-linked glycans contain

A

A common core pentassacharide structre attached to asparagine but differ in temrinal elborations that extend from this core

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31
Q

What is glycoproteins

A

Glycosylate protiens with covalently linked N-glycans and O-glycans glycoprotiens are assembled through the ER-golgi pathway

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32
Q

What is GPI

A

Anchored glycoprotiens contain a specific glycan bridge between lipid anchor and the C-terminus of a protien

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33
Q

What is EGF/TSR

A

Epidmerla growth factor and thrombospondin represent membrane protiens which are glycosylated with only short unbranched carbohydrate structures

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34
Q

What are proteoglycans

A

Are glycoconjugates that have one or more glycoasminoglycans covalently attached to core protien they are linear

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35
Q

What are glycosphingolipids

A

Consists of a glycan usually attached via glucose or glactose to the terminal OH group of the lipid molecule

36
Q

What are lectins

A

Protien that specifically recognizes and binds to glycans without catalyzing a modification of the glycan carbohydrate binding proteins other than immunoglobins that no enzymatic

37
Q

What are lectins

A

Highly specic to individual monosaccharides which can link to other sugars in a complex glycans

38
Q

What domain does lectin have

A

Carbohydrate-recognition domain which is respobsible for binding glycans

39
Q

What do lectins function as

A

Multimers which allows them to bind seceral glycan molecules at a time

40
Q

What happens if you add them to cell suspension

A

Bind cell surface glycans and make bridges between cells inducing cell aggregation

41
Q

How can cell aggregation be detected

A

Spectrophotometrically by mesauring the light transmission of cellular suspension as the suspension of aggregated cells transmits more light than the supesnion of indivudal cells

42
Q

What happens if inhibitory sugard were added

A

No cell aggregation was observed blocks CRD of VAA and GlcNAc blocks the CRD of WGA

43
Q

What are the four types of animal lectins

A
  1. galectins - soluble glactose binding lectins
  2. C-type lectins transmembrane proteins with Ca depedent glycan binding specificiy
  3. P type lectins transmembrane proteisn with aset of immunoglobuin domains
  4. I typed lectins - transmembraen proteins with a set of immunoglbuil domains
44
Q

What are glactins

A

Animal lectins that preferntially recognize B-glactoside containing glycans
Share significant sequence similarties in the CRD
Soluble multifunctional protiens

45
Q

What are the three subfamiles of galectins

A

Proto-type with one CRD
Tandem-repeat type with two different CRDs
Chimeric with one CRD linked to a non lectin N terminal domain

46
Q

Why are galectins important

A

Both inside and outside the cell that perform different functions

47
Q
A
48
Q
A
49
Q

What is the CRD structure

Beta sheets

A

Beta sandwich with two sheets formed by six beta strands on concave side and five on the convex side

49
Q

What does the HL-60 differeninate into

A

Eosinophil like cells
Neutrophil- like cells
Macrophage like cells depending on the type of stimuli

50
Q

How HL-60 cell line maintained

A

It is a suspension cell line
Orignated froma a female patient with acute promyelocytic lukemia
Expresses 6 gallectins

51
Q

What different stressors were used in extracellular stress stimuli

A

Conventional cellular stress exopixa CoCl1
Tunicamycin for ER stress

52
Q

What did the study include after glactein expression and adhesion charactersitics of HS-60

A

manose glactose and sialiac acid and GlvNAc residues are available on the cell surface for cell contancts. The glacteins didnt change the prefrence to the binding of lectins in stress but changed the expression of it

53
Q

What are the four categories of galectin genes are recognize in the context of cellular stress responses

A

Stress inducible
Stress repressed
Stress reistant
Undetectable

54
Q

How can oxidative stress be induced

A

Menadione which creates superoxide radiacal

55
Q

What do HL-60 overexpress in oxidative stress and what does it repre

A

NCF1 gene and HMOX1 and 1, 3 and 10 and 9 was downrefgulates biological signficance network remodeling in conjucation with cellular stress responses

56
Q

What is glycosyltransferase

A

An enzyme that catalyze transfer of a sugar from a sugar nucleotide dononr to substrate these enzymes are responsible for the synthesis of most glycoproteins and other glycoconjugates

57
Q

What are glycosidases

A

Enzymes that catalyze hyrdolysis of glycosidic bonds in glycans: endoglycosidases catalyze the cleavage of internal glycosidic linkage while exoglycosidases cleave a monosaccharide from the terminal end of a glycan

58
Q

What is glycan-degrading enzymes

A

Type of glycosidases that destroy large pollysaccharides

59
Q

What does OGT do

A

Catalyze the transfer of a GlcNAc sugar from the donor substrate UDP-GLcNAx

59
Q

WHere does GlcNAc bind

A

Hydrozyl groups of serine and theronine residues

60
Q

What is OGA

A

Cataylzes the hydrolysis of this sugar modification and removes O-GlcNAc

61
Q

Where does O-GlcNAcylation happens

A

Inside of cells in cytoplasm nucleus and mitochondria

62
Q

How is UDP-GlcNAC produced

A

Is an OGT substrate through the hexosamine biosynthetic pathways

63
Q

What is the rate liminting enzyme in Hexosamine biosynthetic pathway

A

GFAT

64
Q

What is the pathway of hexosamine

A

Fru-6P to GlcN-6P through GFAT
GlcN-6P then produces UDP-GcNaC
This can also be recycled through the salvage pathway which converts GlcNAc back into GlcNAc-6P that can be utilized by the pathway

65
Q

What competes with GlcNAcylation

A

Competes with phosphorylation because both are types of posttranslational modification that target Ser/Ther

66
Q

What complex induces phosphorylation

A

OGA and Kinase

67
Q

What complex induces glycoprotien

A

OGT and phosphotase

68
Q

Where is O-GlcNAcylated most common

A

Cytsol and Nucleus less in endosome and peroxisomes

69
Q

Where are the most O-GlcNacylated protiens and lowest

Body parts

A

Most is in the brain and liver
Least is bones saliva gall bladder and urine

70
Q

What happens when there is elevated O-GlcNA

Disease

A

Contirbutes directly to glucose toxicity in diabetes and cancer

71
Q

What does decreased O-GlcNacylation

A

Alzheimers disease and parkinsons disease tau protien carries O-GlcNAc residueds that compete with key phosphorylation residued and prevents it aggreations

72
Q

What happens to global O-GlcNAc levels

A

They are elveated in response to cellular stress in all cases of they observed signficant increase in intensitniy of bands

73
Q

How do you run the immunodot blot assay

A

Immobilize cellular protiens then incubate the membrane with primary and secondary antibodies
Does not require protein elctrophoresis
Intensinity of dot is proportional to the levels in cells

74
Q

How is the efficnancy confirmed

A

Increasing or decreasing levels of O-GlcNaC in cells treated with OGT inhibitor and OGA inhibitos

75
Q

What was the finding in cellular differentiation

A

Levels of O-GlcNAc significantly decrease in differentiated cells versus progenitor cells

76
Q

What else can O-GlcNAc regulate

A

Protien traffcking and turnover they are less transportable, more stable and usually not secreted from cells

77
Q

What do regulatory fuctions of glacteins depend on

A

Localization of glactins in cells
O-GlcNAc promote intracellular accumulation and where low levels of O-GlcNAc promote galectin secretion can be applied to glactein 3 and 9

78
Q

What is LGALS12 for

A

Highest RNA expression in adipose tissue, breast and bone marrow

79
Q

What is LGALS16

A

Highest RNA expression in normal placenta retina and brain tissues

80
Q

What is the hypothesis of cell culture models to study tissue specefic galectins

A

Increased when cells become more specalized and decreased in cancer might act as tumor supressers and used different cell lines

81
Q

What is the N1 phenotype

A

Showed increased activity of LGALS12 gene and behaved in a way that fights tumors and promtoes inflammation

82
Q

What is the N2 phenotype

A

Showed decreased activity of LGALS12 and behavied in a way that supports tumor growth and reduces inflammation

83
Q

What happend with LGALS16

A

When cells were treated with 8-BR-cAMP that promtoes the cells to mature into trophoblast like cells LGALS216 activity increased significantly CGB confrimed this

84
Q

What is the role of LGALS16 in trophoblastic differentiation of JEG-3 cells?

A

Using CRISPR/Cas9 to knock out (KO) the LGALS16 gene in JEG-3 cells, researchers showed that these KO cells had:
Lower response to 8-Br-cAMP, as seen in reduced CGB expression (both gene and protein levels).
No changes in growth rate when treated with 8-Br-cAMP, unlike control cells.
Conclusion: LGALS16 is essential for trophoblastic differentiation of JEG-3 cells.

Cell Bio (13 decks)

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