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Plant Biotechnology > First half > Flashcards

First half Flashcards

1
Q

What are the three layers of tissue found in plants

A

Ground
Vascular
Epidermis

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2
Q

What are the three types of ground tissue

A

Cortex (chollenchyma)
Fibre Cells (sclerenchyma)
Pith (parenchyma)

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3
Q

Name of cell with no cell wall

A

Protoplast

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4
Q

Ratio of polysaccharides to proteins in cell wall

A

9:1

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5
Q

Where are primary cell walls found and what are their qualities?

A

Around growing cells (parenchyma)

Thin, high water content, simple

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6
Q

Where are secondary cell walls found and what are their qualities?

A

Form around primary cell walls after growth (sclerenchyma)

Thicker, lower water content, complex (lignin)

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7
Q

Give an example of a type of pectin in the cell wall and its purpose

A

Homogalacturonan

Wall hydration and porosity

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8
Q

Give a definition and example of a hemicellulose in the cell wall and its purpose

A

anything thats not cellulose or pectin
xyloglucan
cross links cellulose microfibrils

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9
Q

Where would you find type 1 primary cell walls?

A

dicots, gymnosperms, non graminoid monocot species

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10
Q

Where would you find type 2 primary cell walls?

A

graminoids (cereals, rice)

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11
Q

How do type 1 and type 2 primary cell walls differ?

A

Type 2 has less/no pectin and less xyloglucan than type 1.

Instead it has more arabinoxylan and mixed linkage glucans and phenolic acids!!

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12
Q

Describe wall formation during mitosis

A

Preprophase bands of microtubules and actin filaments gather round middle
Golgi derived vesicles are transported to this point round the centre of the cell
This forms the beginning of cell plate (phragmoplast)
Cytokinesis occurs
Secondary cell wall not formed until after differentiation

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13
Q

How many times over can a plant cell double in size after mitosis?

A

100

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14
Q

How does cell expansion occur?

A

Loosening of cell wall causes water to move in via osmosis and the stretched, thinner wall can then have extra material added to it.

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15
Q

Which polysacharride is dislodged by cell loosening enzymes?

A

cross linking hemicellulose (e.g. xyloglucans)

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16
Q

Describe two types of growth

A

Diffuse growth - all cells within the tip grow equally and proportionately
Focus growth - only cells at the very tip elongate while others stay equal in size

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17
Q

Explain diffuse growth and where it occurs

A

Occurs in the zone of elongation behind tip
Growth of cellulose microtubules latitudinally around the cell means growth is restricted to one direction.
Disrupting this by, for example, a herbicide oryzaline causes rounded growth of cells.

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18
Q

Explain focus growth (tip growth)

A

Highly localised and carried out by the movement of vesicles containing cell wall material along actin molecules. Once again suppling an inhibitor of actin growth (Brefeldin A) stops tip growth.

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19
Q

What growth occurs in epidermal cells?

A

Both diffuse and tip growth like a jigsaw puzzle.

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20
Q

What does rotation of the C4 hydroxyl in alpha glucose form?

A

alpha d galactose

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21
Q

What does oxidation at C6 of alpha glucose form?

A

alpha d glucaronic acid

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22
Q

What does rotation of the C2 hydroxyl in alpha glucose form?

A

alpha d mannose

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23
Q

What is the monosaccharide and bond in cellulose?

A

Beta glucose and a 1-4C glycosidic bond

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24
Q

What is the monosaccharide and bond in starch?

A

Alpha glucose and a 1-4C glycosidic bond

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25
Q

Which polysacharride displays a rigid structure with H bonds?

A

Cellulose

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26
Q

Describe structure of xyloglucans

A

Cellulose backbone with xylose residues (sugars such as galactose and fucose) attached to C6 on 3 out of 4 glucose molecules.

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27
Q

How does xyloglucan contribute to the primary cell wall

A

In type 1 it acts as a cross link interacting non covelently with cellulose.

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28
Q

What are the role of nucleosides in the glycosylation reactions

A

sugar donor to build up cellulose strands

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29
Q

What are the most common glycosyl donors?

A

UDP (uridine diphosphate)/GDP (guanine diphosphate)

30
Q

What happens to the NDP (nucleoside diphosphate) after the glycosidic bond is formed?

A

It is released and recycled to act as a donor again.

31
Q

Name the two types of enzymes used in the formation of cell wall polysacharrides

A

Polysaccharide synthases - for backbone formation and inverting monosacharides to create beta bonds
Glycosyl transferases- for building individual monosacharides onto a xyloglucan side chain.

32
Q

Where are unbranched polysaccharides formed? (cellulose)

A

Straight onto the cell wall on plasma membrane

33
Q

Where are branched polysaccharides formed? (xyloglucan type 1 and arabinoxylan type 2)

A

Within vesicles in the golgi apparatus.

34
Q

What are the 4 parts of a golgi located glycosyl transferase?

A

Cytoplasmic tail, transmembrane region, stem region, catalytic domain.

35
Q

What is the role of a glycosyl tranferase enzyme in the case of xyloglucan?

A

Xyloglucan xylosyl transferase adds a single xylose residue to the cellulose backbone of xyloglucan.

36
Q

What is the name of the hexameric structure producing cellulose microfibrils, where is it positioned and how many cellulose chains are in each microfibril?

A

Cellulose Synthase - Rosette on the plasma membrane 18-24 chains

37
Q

How many times does a cellulose synthase (CesA) molecule cross through the plasma membrane?

A

8

38
Q

What is the repeated motif of amino acids found in the cytoplasmic catalytic domain of the cellulose synthase?

A

DDDQxxRW (D=aspartic acid Q=glutamine x=any amino acid R=Arginine W=trytophan

39
Q

How many types of CESA genes are in Arabidopsis?

A

10

40
Q

Describe the trimer model of a rosette.

A

Each rosette has a total of 18 CESAs with each subunit containing 3 CESAs.

41
Q

What guides the positioning of cellulose strands?

A

Cortical Microtubules

42
Q

What two substances can seeds store carbon as?

A

Oils and starch

43
Q

What are the two main oilseed crops?

A

Palm and soy

44
Q

How much is edible oil consumption predicted to rise by 2020?

A

From 20kg->25kg

45
Q

What % of canola export from Oz goes to the EU for biodiesel production and how much is it worth?

A

70% - $900 million

46
Q

Name 4 GM oilseed crops

A

Soybean, maize, cotton, canola

47
Q

What 4 qualities to we look to change when genetically engineering oilseed crops?

A

Modify chain length
Degree of Saturation
Fatty Acids
Ratio of oil to protein

48
Q

If I write petroselenic (18:1 delta 6) what can you deduce about this fatty acid?

A

It has 18 Cs with one unsaturated (double) bond in the position of the sixth C.

49
Q

Define an oil

A

It is a type of lipid usually liquid at room temperature. It is made up of fatty acids normally attached by an ester bond to a glycerol molecule

50
Q

Describe the structure of a triacylglyceride, starting first with the initial structure of glycerol.

A

Glycerol is a three carbon molecule with alcohol groups attached to all three carbons. These alcohol groups go on to form an ester bond with three fatty acids to make a triacylglyceride.

51
Q

Name three common fatty acids

A

Stearic (main one in mammals), lenoleic, oleic (olive oil), palmitic

52
Q

Does having a double bond always affect the shape of the fatty acid?

A

No, trans bonds have the chain leaving the double bond at opposite positions hence a kink is not introduced - however these are notoriously unhealthy.

53
Q

How does the position of the double bond affect the melting point of a lipid?

A

The closer to the middle of the fatty acid chain, the lower the melting point (more disruptive shape).

54
Q

Outline the basic oil biosynthesis pathway (it’s not so basic)

A

Phosphoenol pyruvate (PEP) is converted to pyruvate in a plastid.
This becomes acetyl-CoA before joining with a carbonate ion (carboxylase enzyme) to become Malonyl CoA.
This goes through an enzyme called fatty acid synthetase (FAS) and, no surprise, forms free fatty acids.
These are transferred to the endoplasmic reticulum where a series of acyl transferases attach the fatty acids to a glycerol molecule (from glycerol 3 phosphate G3P).

55
Q

Describe what an oil body does and its structure

A

This is where TAGs (triacylglycerides) accumulate and are made up of a half unit membrane (monolayer of phospholipids) and a high proportion of oleosin, an emulsifier to keep the oil body suspended.

56
Q

What are the main fatty acids found in firstly soy then palm?

A

soy: 18:1 and 18:2 palm 18:1 and 16:0

57
Q

Give an example of a selectively bred crop based on their oil content

A

Canola has been bred with a high erucic acid content as it makes a good fuel but this is impactful on human health so has also been bred with a low erucic acid content too for consumption.

58
Q

Give examples of gene modification where a function is added and also removed

A 
Added = lauric acid production 
Removed = Steroyl ACP desaturase
59
Q

Why is it valuable to be able to produce lauric acid in temperate regions in canola?

A

Primary ingredient in many shampoos and detergents but current production tends to be in areas of political instability making prices equally unstable

60
Q

What step must be undertaken in canola to result in the production of lauric acid

A

Must have a higher ratio of FATB thioesterase (decides where C chain is cleaved) since this produces shorter chains (lauric acid only 12 Cs) than FATA thioesterase (most dominant in canola).

61
Q

Where did scientists look for FatB enzyme and which part of the plant is it found in?

A

In California Bay plant (relative of bay for cooking) Thioesterases are found only in seeds (deliterious elsewhere).

62
Q

Describe the gene construct required to express MCTE (medium chain thioesterase) in California Bay.

A
  • Seed specific promotor region (can come from a seed storage protein called Napin to give high levels of expression)
  • Fat B coding region (includes targetting sequence already aimed towards plastid so does not need adjustment)
  • Any stop codon
63
Q

What is the most common way to quantify fatty acid content in oils? Describe the process

A

Gas chromatography - Oils injected into column and vapourise moved along by an inert gas. They then seperate based on how they adsorb to the column.

64
Q

Why can lauric acid production never reach above 60% in Brassica?

A

The acyl transferase cannot attach short chain fatty acids to the second C of glycerol molecule so it can never have more than 2/3 fatty acids. Coconuts preferable.

65
Q

Why is it useful to remove stearoyl ACP-desaturase?

A

It converts stereate to 18:1 which is unstable and cannot withstand cooking at high temperatures.

66
Q

Where in the fatty acid synthase pathway does stearoyl ACP-desaturase act?

A

After the FAS cycle and before the fatty acids are transferred to the endoplasmic reticulum

67
Q

How is the gene edited to stop stearoyl ACP expression?

A

The gene is rotated into the antisense orientation (backwards)

68
Q

What can Linolenic and Linoleic acid be converted to?

A

arachidonic acid ARA or eicosapentaenoic acid EPA

69
Q

What are ARA and EPA precursors for and where are they found?

A

ARA inflammatory precursor found in omega 6 foods (grain fed meat) EPA anti-inflammatory precursor found in omega 3 foods (oily fish)

70
Q

What steps must be taken to increase levels of Stereadonic acid (SDA) in soybeans?

A

Increase delta 6 desaturase enzyme but also conversion of linoleic acid to linolenic.

Plant Biotechnology (10 decks)

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