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BIOLOGY-FY > S1-L3: Carbohydrates > Flashcards

S1-L3: Carbohydrates Flashcards

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1
Q

Define and describe “carbohydrates”

A
  • Biological molecules containing C, H and O atoms
  • empirical formula generally Cn(H2O)n
  • fundamental cellular components vital for cellular function
  • also termed “saccharides”
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2
Q

What is a “saccharide”?

A

-organic compound containing sugar(s)

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3
Q

Outline the function(s) of carbohydrates (refer to figure 1/2/3)

A

1-provide rapid & readily available energy supply for cellular reactions- E.G: muscle + liver glycogen
2-form part of important molecules in cell
–> such as sugar-phosphate backbone in DNA double helix
3-form markers on cell surface which aids cell recognition
–> like blood group markers

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4
Q

Briefly outline the following classifications of carbohydrates:

1-Monosaccharide
2-Disaccharide
3-Oligosaccharide
4-Polysaccharide

A

1- General formula (CH2O)n
2- dimer–> 2 monosaccharides
3- polymer of 3-20 monosaccharides
4- polymer of monosaccharide units linked together

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5
Q

Describe monosaccharides

A
  • C atoms range 3-10
  • simplest carbohydrate ends in “-ose”
  • single sugar molecules providing instant energy
  • contain aldehyde/ ketone F. Group AND hydroxyl groups
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6
Q

What are the names for the first 3-10 monosaccharides?

A

-3 c’s- triose/ 4 c’s- tetrose/ 5 c’s- pentose/ 6 c’s- hexose/ 7 c’s- heptose/ 8 c’s- octose/ 9 c’s- nonose/ 10 c’s- decose

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7
Q

What is the structure of aldehydes/ ketones and hydroxyl groups?

A
  • Aldehyde: R(C=O)H
  • ketone: R(C=O)R
  • hydroxyl group: ROH
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8
Q

Describe the nomenclature of “Fischer projections”

A

-Count C atoms from top- top from aldehyde/ ketone group

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9
Q

Refer to the diagrams of Glucose and Fructose- Figure 5/6

A
  • 6C sugar- aldohexose has aldehyde group

- 6C sugar- ketohexose has ketone group

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10
Q

Outline how the molecules in figure 7 differ and chemical formula for them

A
  • Hydroxyl group position differs between different sugars
  • distinct aldohexose sugars with same chemical formula
  • -> C6H12O6
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11
Q

What are N-deoxymonosaccharides (refer to figure 8)?

A
  • Can exists as “deoxy” forms

- -> hydroxyl (OH) replaced with H

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12
Q

Define and describe “stereoisomerism”

A
  • Have same chemical formula/ orders AND bond types
  • ->are non-overlapping mirror images of each other
  • ->so have different spatial arrangements AND different biological functions
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13
Q

In what two forms can you find stereoisomers?

A

-D or L isomers

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14
Q

How are stereoisomers formed?

A
  • require chiral C centre
  • -> C chiral if has 4 different groups attached to it
  • -> at least one chiral C needed for stereoisomerism
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15
Q

Outline how sugars are assigned as L or D isomers

A
  • Use Fischer projections with most oxidised C at top
  • If OH on bottom chiral centre points to right–> D
  • If OH on bottom chiral centre points to left–> L
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16
Q

Which of the two isomers, L or D glucose, are more common and why?

A
  • D as predominant energy source in cellular respiration
  • L not as common as biologically inert in bodies
  • -> can’t provide us with energy even though structure same as D-glucose
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17
Q

How may monosaccharides exist as cyclic structures and how do they form? (refer to figure 9)

A
  • monosaccharides exist as open-chain OR ring (cyclic) structure joined by covalent bond
  • process: OH group on second to last C atom reacts with carbonyl group
  • monosaccharides cyclize under normal conditions
  • ->only small amount of straight chain present
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18
Q

What would the cyclized product for Aldose and Ketose be?

A
  • Aldose; Hemiacetal

- Ketose: Hemiketal

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19
Q

Describe the cyclization of D-glucose (refer to figure 10)

A
  • OH group able to attack C=O group either side- so 2 possible hemiacetal products
  • -> a and b anomers of D-glucosepyranose
  • cyclic form of D-glucose is D-glucosepyranose
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20
Q

Outline glucose and its function(s) (figure 11)

A
  • primary energy source of life
  • 7 energy-rich C-H bonds
  • bonds broken down during cellular respiration
  • released energy stored as ATP for cell use
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21
Q

Describe the structure and function of fructose (figure 12)

A
  • 7 rich C-H bonds
  • forms furan-based ring structure despite being hexose (6C)
  • furanose–> 5 membered cyclization product
  • important energy source alongside glucose AND galactose
  • found in fruits/honey/berries and lemon
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22
Q

Define and briefly explain the formation of “disaccharides”

A
  • 2 monosaccharides linked together like sucrose/ maltose/ fructose
  • formed by dehydration reaction synthesis- condensation reaction where H2O lost
  • molecules joined at -OH groups by glycosidic bond
  • biological catalyst (enzymes) aid reaction
  • multiple configuration possible
23
Q

What is the primary function of disaccharides?

A

-nutritional source of monosaccharides

24
Q

What is maltose and it’s function? (figure 13)

A
  • 2 glucose molecules joined at C 1 and 4 via an a-1, 4 glycosidc bond (via condensation reaction)
  • primary function is as nutritional source of monosaccharide
25
Q

Where can starch be found?

A
  • can generate from starch (polysaccharide) breakdown

- found in germinating seeds AND grain AND metabolism of maltose by yeast yields ethanol + CO2

26
Q

How may starch be broken down?

A

-enzyme maltase digests maltose down in to individual monosaccharides

27
Q

What is lactose? (figure 14)

A
  • glucose + galactose molecules joined at C 1 + C 4

- B-1, 4 glycosidic bond (C1 OH group above glucose ring)

28
Q

How is lactose produced?`

A

-produced by lactating mammals as energy source for young

29
Q

Which enzyme is needed to digest lactose and what products are produced?

A
  • digested to glucose + galactose

- enzyme lactase needed

30
Q

Outline the structure of sucrose (figure 15)

A

-Glucose + fructose molecules joined at C 1 + C 2 via an a-1, 2 glycosidic link

31
Q

Where is sucrose found?

A
  • abundant in plant/ sap especially sugar cane AND sugar beet
  • plentiful in western diet (sugar)
32
Q

What is digested products of sucrose and the enzyme needed for this process?

A
  • digested to glucose + fructose

- enzyme sucrase needed for this process

33
Q

What is a hydrolysis reaction?

A

-cleavage of chemical bonds by water addition

34
Q

Describe the breaking down of disaccharides

A
  • gylcosidic links in disaccharide broken in to constituent monosaccharides during digestion
  • ->reaction requires H2O + specific enzyme in gut
  • monosaccharides more easily absorbed through gut lining
35
Q

Outline reactions for digestion of:

1-maltose
2-lactose
3-sucrose

A

1- Maltose–> Glucose + glucose (maltase)
2- Lactose–> Glucose + Galactose (lactase)
3- Sucrose–> Glucose + Fructose (sucrase)

36
Q

Which two polysaccharide components does starch consist of?

A

-Amylose and amylopectin

37
Q

Outline the structure of:

1-amylose
2-amylopectin

refer to figure 16 and 17 respectively

A

1- long linear chains of a-1, 4-linked D-glucose residue
–> has coiled structure
2- linear chains of a-1, 4-linked D-glucose residue joined via a-1, 6 linked branch points
–> has brush-type of structure

38
Q

What is the function of starch and where is it found?

A
  • Main dietary source of carbohydrate
  • main storage polymer in plants
  • found in amyloplasts + chloroplasts of plant cells from roots/ tubers/ seeds & fruits
39
Q

Describe “amyoplasts” and their function

A
  • non-pigmented plant cell organelles

- responsible for synthesis AND storage of starch granules via polymerisation of glucose

40
Q

Breakdown of Starch after eating:

What is the role of amylase/maltase?

A

-brekdown a-1, 4 glycosidic links

41
Q

Outline the role of isomaltase

A

-breaks down a-1, 6 glycosidic links

42
Q

What is the process of starch digestion to glucose?

A
  • Amylase (in saliva + gut) digests/ maltase + isomaltase (gut only)
  • -> to dextrins (oligosaccharides/ maltoriose/ maltose/ isomaltose)
  • -> then ultimately glucose
43
Q

What is glycogen? (refer to figure 18)

A

-complex branched polysaccharide of linear chains of a-l, 4-linked D-glucose residue joined through a-1, 6-linked branch point

44
Q

Describe the structure of glycogen

A
  • structure similar to amylopectin BUT branch points occur more frequently
  • ->every 8-12 residues VS 24-30 in amylopectin
45
Q

What is use glycogen?

A
  • main storage polymer of animals–> found in liver AND muscle cells
  • readily hydrolysed to glucose when energy needed
46
Q

Outline the effect of fasting/ starving on an individual in terms on glucose/ starch

A
  • blood generally contains 5-6mM glucose any given time
  • ->starving/fasting individual attempts to maintain level outlined above at expense of glycogen stores in liver/ muscle cells
47
Q

Define glycoproteins and their importance

A
  • proteins which contain oligosaccharide chains attached covalently to protein structure
  • glycosylated membrane proteins play important role in immune recognition
  • secreted glycoproteins make up mucins AND glycocalyx
48
Q

Briefly explain what Mucins are

A
  • Principal components of mucus by mucous membranes (lining of body cavities open to exterior) AND as saliva components
  • Glycocalyx Glycoprotein covering surrounding cell membranes
49
Q

Describe the glycocalyx

A

-Glycocalyx glycoprotein covering surrounding cell membranes of epithelial/ bacteria and other cell types

50
Q

What are glycolipids?

A

-Lipids which contain oligosaccharide chains covalently attached to their lipid structure

51
Q

Where are glycolipids generally found and how does this relate to their function?

A
  • often associated with phospholipids on outer surface of cell membrane
  • ->in such cases usually function as recognition signals/ attachment factors/ membrane stabilisers
52
Q

Define a “sphingolipid”

A
  • subtype of lipid which include
  • -> ceramide (signalling molecule)
  • sphingomyelin (membranes)
53
Q

What are “glycosphingolipids”?

A
  • Cerebrosides–> found in muscles and nerves

- Gangliosides–> found in plasma membranes

54
Q

Summary of lecture

A
  • Carbohydrates contain C/ H/ O atoms
  • -> formula Cn(H2O)n
  • monosaccharides have chiral C which determines stereochemistry–> D VS L
  • monosaccharides join together to form di-, olgi- and polysaccharides
  • polysaccharides have key functional roles–> starch glycogen
  • glycoproteins AND glycolipids have important structural roles–> glycocalyx/ glycosphingolipids

BIOLOGY-FY (12 decks)

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