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Cell Processes Flashcards

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1
Q

What bases are pyrimidines?

A

Cytosine

Uracil

Thymine

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2
Q

How can you distinguish pyrimidine structures from one another?

A

Cytosine possesses an NH2 group

Uracil has a CH whilst thymine has a methyl group at the same Carbon

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3
Q

What bases are purines?

A

Guanine and adenine

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4
Q

How can you distinguish between the structures of purines?

A

Guanine possesses a C=O bond whereas adenine does not

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5
Q

What is the structural difference between deoxyribose and ribose?

A

Ribose possesses two OH groups on the same side but deoxyribose only has one

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6
Q

What is the structure of a steroid?

A

4 cyclic groups (usually 3 hexagons + 1 pentagon)

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7
Q

List the three macromolecule types:

A

Polysaccharides (carbohydrates)

Proteins

Nucleic acids

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8
Q

What is a macromolecule?

A

Polymers constructed of identical or similar monomers - very large

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9
Q

What are two ways macromolecules can be made/broken?

A

Via dehydration or hydrolysis reactions

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10
Q

Are lipids soluble in water? Why?

A

Lipids are not soluble in water as they are non-polar. This is due to the fact that they are mostly composed of non-polar hydrocarbon chains

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11
Q

What is the structure of a lipid?

A

Glycerol + 3 long chain fatty acids

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12
Q

How does the structure of a lipid differ from that of a phospholipid?

A

One of the fatty acids in phospholipids is replaced with a phosphorus group

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13
Q

What is the function of lipids?

A

Essential component of cell membrane (cholesterol)

Stores energy as fat

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14
Q

What kind of linkages are formed when a lipid is created? What kind of reaction is this!

A

Dehydration reaction - ester linkages x3

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15
Q

What is the difference between a fully saturated fat and an unsaturated fat?

A

Saturated - no more h able to bind, straight

Unsaturated - double bonds present, bent

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16
Q

What is a polysaccharide composed of?

A

Simple sugar monomers

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17
Q

Name 3 simple sugars

A

Glucose

Galactose

Fructose

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18
Q

What are the names for polysaccharides containing 1 simple sugar, 2 simple sugars and 3+ simple sugars?

A

1 - monosaccharide
2 - disaccharide
3+ - polysaccharide

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19
Q

Give 3 examples of a disaccharide

A

Lactose - glucose + galactose

Maltose - glucose + glucose

Sucrose - glucose + fructose

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20
Q

What is a glycosidic linkage?

A

A bond between a sugar and another group (may be another sugar)

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21
Q

What is the function of a polysaccharide?

A

Energy storage (glycogen in animals and starch in plants)

Structural function (chitin in animals and cellulose in plants)

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22
Q

What is the structure and function of starch?

A

Function: energy storage for plants - hydrolysed when needed

Structure: glucose polymer

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23
Q

What is the structure and function of glycogen?

A

Function: energy storage in animals - hydrolysed when needed

Structure: glucose polymer, more extensively branched than starch

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24
Q

What is the structure and function of cellulose?

A

Function: Structural building block of plants - can hydrogen bond to others to form myofibrils (as strong building material)

Structure: beta-glucose polymer, never branched, has different glycosidic linkages to starch which results in a distinct 3D shape

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25
Q

What is the structure and function of chitin?

A

Function: structural building block of animals

Structure: similar to cellulose with beta-glucose linkages, but also contains nitrogen

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26
Q

What is the structure of a protein?

A

Molecules built up from 20 different amino acids linked together via peptide bonds

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27
Q

What is the function of a protein? (7)

A

Enzymes

Defence

Storage

Transport

Cellular communication

Movement

Structural support

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28
Q

What are the 3 R group side chain properties?

A

Non polar

Polar

Electrically charged

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29
Q

What part of an amino acids comprises the polypeptide backbone?

A

Non R group parts (amino group, alpha carbon, carboxyl group)

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30
Q

Are the R groups the same in each amino acid?

A

No, the R group differs from one type of amino acid to the other

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31
Q

What is the structure of a nucleic acid?

A

Long unbranched molecule

Backbone made of ribose or deoxyribose linked via phosphodiester bonds

Side groups (bases) are pyrimidines or purines

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32
Q

What is the function of nucleic acids?

A

Codes for genetic material

All informational processes include these macromolecules

Storage of chemical energy in ATP

intracellular signalling via cAMP

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33
Q

What is the difference between a nucleotide and a nucleoside?

A

Nucleotide consists of phosphate group, sugar, and base

Nucleoside lacks the phosphate group, and consists of just the sugar and base

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34
Q

Describe the fluid mosaic model for the phospholipid bilayer

A

Phospholipids + proteins studded throughout membrane (protein placement not random, corresponds to defined specialised patches)

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35
Q

Define amphipathic

A

Molecules that are both hydrophilic and hydrophobic

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36
Q

Fully saturated hydrocarbon tails lead to an increase in _____ and a decrease in _____

A

Increase in viscosity

Decrease in fluidity

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37
Q

Unsaturated carbon tails lead to an increase in _____ and a decrease in _____

A

Increase in fluidity

Decrease in viscosity

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38
Q

What is cholesterol regulation?

A

“Fluidity buffer”

Cholesterol retains gaps between phospholipids

Reduces fluidity at high temperatures

Prevents solidification at low temperatures

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39
Q

What is the difference between a peripheral and an integral protein?

A

Peripheral proteins do not penetrate the phospholipid bilayer

Integral proteins do

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40
Q

Name the 6 functions of membrane proteins

A

Signal transduction

Attachment to cytoskeleton and extracellular matrix

Transport

Intercellular joining

Cell-cell recognition

Enzymatic activity

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41
Q

What types of molecules can easily cross the lipid bilayer?

A

Non polar molecules - hydrophobic and can dissolve in and cross the lipid bilayer

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42
Q

What kinds of molecules will find it hard to cross the lipid bilayer without assistance? Which will travel across slower unassisted?

A

Polar molecules - hydrophilic - impeded by hydrophobic interior of lipid bilayer

Ions - cross more slowly than polar molecules

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43
Q

List two types of transport proteins and their functions. Are transport proteins specific for molecules or non-discriminating？

A

Transport proteins are specific for the substance it translocates.

Channel proteins - provide hydrophilic channel so certain molecules and ions can cross (called ion channels for ions)

Carrier proteins - shuttle molecules across membrane by changing shape

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44
Q

What is selective permeability dependent on?

A

The discriminating barrier of the lipid bilayer + specific transport proteins built into the membrane

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45
Q

What are two types of transport small molecules can use to get across the lipid bilayer?

A

Passive transport

Active transport

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46
Q

What is passive transport?

A

No work done (no energy expended)

Molecules diffuse down its own concentration gradient from high concentration to low concentration

Can be facilitated via the aid of proteins

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47
Q

What kinds of proteins are utilised in active transport? What is active transport?

A

Carrier proteins are utilised in active transport

Movement of molecules against their concentration gradient (low conc. to high conc.)

Work done (energy used in process of active transport)

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48
Q

Give an example of active transport

A

Sodium-potassium pump

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49
Q

Describe the cycle of the sodium-potassium pump

A

An increased affinity for sodium means cytoplasmic sodium bind to the sodium-potassium pump

The binding of sodium stimulates phosphorylation by ATP (atp transfers terminal P group directly to transport protein)

Phosphorylation causes the carrier protein to change shape, reducing its affinity for sodium and increasing its affinity for potassium

Sodium leaves carrier protein, extracellular potassium binds to carrier protein

Binding of potassium triggers the release of the phosphate group

The loss of the phosphate group results in a lowered affinity for potassium and an increased affinity for sodium. Potassium leaves the carrier protein and the process repeats.

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50
Q

What is membrane potential?

A

The voltage across a membrane - affects charged substances across the membrane

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51
Q

In regards to the extracellular matrix, is the inside of the cell more positively or negatively charged? What does this mean for ions travelling across the membrane? How does this occur?

A

The cell is more negatively charged, the outside is more positive.

Membrane potential favours the entry of cations and the exit of anions.

Voltage is generated via an electrogenic pump such as the sodium-potassium pump (3Na+ out, 2K+ in results in a net loss of one +ve charge per “pump”)

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52
Q

What are the two ways through which large molecules travel to and from the cell?

A

Exocytosis - secretion via fusion of vesicles with plasma membrane

Endocytosis - pinocytosis and phagocytosis

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53
Q

List two types of pinocytosis and their processes

A

Pinocytosis - cell “drinking” - engulfs extracellular fluid - non selective

Receptor mediated endocytosis - appropriate molecule binds to receptors on extracellular side of membrane, surface depresses to form coated vesicle

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54
Q

What is a ligand?

A

A molecule that binds specifically to a receptor site on another molecule

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55
Q

What is a proteoglycan composed of?

A

Protein + carbohydrate chain (covalently bonded)

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56
Q

What is a proteoglycan complex?

A

Proteoglycans noncovalently attached to a single long polysaccharide

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57
Q

What is the function of a fibronectin?

A

Binds extracellular matrix to the cell

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58
Q

What is an integrin?

A

A pair of proteins that span the membrane; attachment point for extracellular membrane and microfilaments

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59
Q

Wha is an example of a cell junction in a plant? Describe its structure.

A

Plasmodesmata - cell walls perforated with channels that connect the cytoplasm of cells (cytosol travels between cells through plasmodesmata)

60
Q

Name 3 types of cell junctions found in an animal cell and their functions

A

Tight junctions - plasma membranes pressed tightly together, bound by proteins (occludins and claudins) - seal intercellular space

Gap junctions / communicating junctions - channels between cells composed of 2 connexons (hemichannels) each composed of 6 connexins

Desmosomes / anchoring junctions - fastens cells together in strong sheets via cadherin proteins, intermediate filaments (keratin) anchor the desmosomes to the cell

61
Q

What are some functions of proteins? (8)

A

Enzymes

Defensive proteins

Storage proteins

Transport proteins

Hormones

Receptors

Contractile / motor proteins

Structural support

62
Q

What determines how a polypeptide chain folds and its final structure?

A

The sequence of side chains in the amino acid monomers

63
Q

What is the primary structure of proteins?

A

Linear arrangement of amino acids and side chains in a polypeptide

64
Q

What is the secondary structure of proteins?

A

Alpha helix - cook held together by hydrogen binding on every 4th amino acid

Beta pleated sheets - beta strands connected by H binds between parts of two parallel segments of polypeptide backbone

65
Q

What is the tertiary structure of proteins?

A

The overall shape of the polypeptide resulting from interactions between side chains (R groups) of the various amino acids.

66
Q

List three types of interactions found in tertiary proteins

A

Hydrophobic interactions - non polar sidechains end up in clusters towards core of the protein - van der waals interactions hold them together

H bonds between polar side chains and ionic bonds between +ve and -ve side chains help stabilise structure

Disulphide bridges - further reinforce shape of a protein (-S-S- rivets part of protein together)

67
Q

What is the quaternary structure of a protein?

A

Association of two or more polypeptides as a functional molecule.

Not all proteins reach quaternary structure.

68
Q

What happens to protein structure following denaturation?

A

Weak chemical binds and interactions disrupted/destroyed - only primary structure retained

69
Q

Can proteins refold/renature?

A

Only in some cases, once normal environments have been restored.

70
Q

What factors can contribute to denaturation of a protein? (5)

A

pH

Temperature

Salt concentration

Reducing agents

Transfer from an aqueous environment to a nonpolar solvent

71
Q

What is the difference between the denaturation and hydrolysis of proteins?

A

Denaturation results in a primary structure

Hydrolysis breaks the structure down even further into monomers

72
Q

What is a chaperonin/chaperone protein and are some of its functions?

A

Chaperonins assist in polypeptide folding by protecting the polypeptide from disruptive chemical conditions while it folds spontaneously. May also provide a more favourable environment for folding.

  • keeps polypeptide separated
  • minute amounts of water present - hydrophilic environment
  • molecular systems interact with chaperonin to check for correct folding
  • can refold misfolded proteins or mark them for destruction
73
Q

What is the difference between an anabolic and catabolic reaction?

A

Anabolic - endergonic - e consumed in reaction, products possess higher E - large molecules from small molecules

Catabolic - exergonic - energy released through reaction - small molecules from large molecules

74
Q

What does an ATP cycle combine?

A

The ATP cycle couples endergonic and exergonic reactions to drive one another

75
Q

Why is ATP used as an energy source for driving cellular work?

A

ATP possesses a higher reactant energy relative to products (ADP+Pi) due to its negatively charged phosphate groups = increased repulsion forces = decreased stability = increased energy

This results in more net energy released than most molecules undergoing similar reactions

76
Q

How do enzymes speed up (catalyse) reactions?

A

Enzymes provide an alternate pathway for reactions to take without lowering the 🔺G

  • may decrease E needed to reach transition state by stretching substrates
  • may provide a more appropriate environment (e.g pH)
  • amino acids in active site may directly participate in the chemical reaction
77
Q

What is a cofactor?

A

Many enzymes require non-protein “helpers” called cofactors for catalytic activity

May bind permanently or reversibly alongside substrate

78
Q

How do cells regulate their metabolic pathways?

A

Switching on/off genes that encode for particular enzymes

Regulating enzyme activity once made

79
Q

How do cells regulate enzyme activity once they are made?

A

Converting between inactive and active forms

Cellular localisation (e.g enzymes locked inside lysosomes)

Allosteric regulation (inhibition or activation) - e.g feedback inhibition

80
Q

What is allosteric regulation?

A

Where a protein’s function at one site is affected by the binding of a regulatory molecule to a separate site - may result in inhibition or stimulation of an enzyme’s activity

81
Q

What is a regulatory/allosteric site?

A

Where an activating or inhibiting regulatory molecule binds - usually located where subunits join

82
Q

What does an enzyme complex oscillate between?

A

The catalytically active and inactive shapes

83
Q

What is the difference in function between an activator and inhibitor (regulatory molecules) on an enzyme complex?

A

Activator - stabilises active form of enzyme complex

Inhibitor - stabilised inactive form of enzyme complex

84
Q

What happens when one unit of an enzyme complex changes shape?

A

The shape change is transmitted to all other subunits.

85
Q

What is feedback inhibition?

A

Where a metabolic pathway is halted by the inhibitory binding of its end product to an enzyme that acts early on in the pathway.

  • more product = less demand
  • product binds to enzyme, inhibiting further production
  • as product is used up by cell, less enzymes are inhibited = more production of the same product
86
Q

What is the sugar phosphate backbone of DNA composed of?

A

A phosphate group covalently bonded to deoxyribose via a phosphodiester bond

87
Q

What is a chromosome’s components?

A

DNA packed together with proteins

88
Q

What is a histone

A

A protein that binds tightly to negatively charged DNA

89
Q

What is a nucleosome?

A

DNA would twice around a core of 8 histones

90
Q

What points outwards from a nucleosome?

A

The amino end (N terminus) / histone tail extends outward from the nuclesome

91
Q

How is the 30-nm fibre formed?

A

Interactions between histone tails of different nucleosomes result in chromatin coiling/folding

92
Q

What is a looped domain?

A

Loops formed by 30-nm fibre become looped domains which are attached to a chromosome scaffold composed of proteins ; 300-nm fibre

93
Q

What is the 300-nm fibre?

A

Looped domains attached to a a chromosome scaffold composed of proteins

94
Q

Put the following in order from smallest to largest:

Nucleosome, 30-nm fibre, 300-nm fibre, histone, looped domain, chromosome

A

Histone

95
Q

Is the interphase chromosome or metaphase chromosome more condensed?

A

The metaphase chromosome is more condensed as it is it undergoing mitosis

The interphase chromatin is less condensed than when preparing for mitosis

96
Q

Is the structure of an RNA molecule more or less variable than that of DNA

A

More variable than DNA

97
Q

What specifies the sequence of bases for RNA?

A

The sequence of bases in DNA specify the sequence of bases for RNA

98
Q

List the 3 types of RNA and their functions

A

rRNA - ribosomal RNA: makes up ribosomes and comprises the bulk of cellular RNA as it is a stable RNA, synthesised from highly repetitive DNA in the nucleus

mRNA - messenger RNA: conveys information from DNA in nucleus which specifies amino acid sequences of polypeptides, synthesised and degraded at a fast rate so is present only in small amounts (live fast die young lol)

tRNA - transfer RNA: possesses an anticodon and amino acid attachment site, translocates nucleotide sequence in mRNA into amino acids during protein synthesis. Possesses 4 base paired regions, 3 loops containing anticodon, amino acid attachment site. There is at least one specific tRNA for each of the 20 amino acids

99
Q

What is an origin of replication?

A

Where DNA replication initiates (1 in prokaryotes, multiple in eukaryotes)

100
Q

What is the function of helicase in DNA replication

A

Helicase breaks H bonds between strands, untwists double helix at replication fork

101
Q

What is the purpose of single strand binding proteins in DNA replication?

A

Single strand binding proteins prevent separated DNA strands from reconnecting

102
Q

What is the role of topoisomerase in the process of DNA replication?

A

Relives strain of DNA twisting ahead of replication fork by breaking, swivelling and rejoining DNA strands.

103
Q

What is the role of primate in DNA replication?

A

Adds primer (complementary RNA chain) to DNA template strand as DNA polymerase can only add to an existing chain

104
Q

What is the role of DNA polymerase in the process of DNA replication?

A

DNA polymerase catalysed the synthesis of DNA by adding nucleotides

Can only add to the 3’ end of primer

105
Q

How are the leading and lagging strands synthesised?

A

Leading: continuously synthesised in 5’ to 3’ direction

Lagging: discontinuous synthesis of fragments (Okazaki fragments)

106
Q

Describe the process of the synthesis of the lagging strand

A

Each Okazaki fragment primed separately

DNA polymerase III adds nucleotides to primer which results in the first Okazaki fragment, detaches when it reaches the next primer

Next fragment primed, DNA polymerase III adds nucleotides, detaches when it reaches the primer of the previous Okazaki fragment.

DNA polymerase I replaces RNA in primers with DNA

DNA ligase forms bond between DNA fragments by joining the sugar-phosphate backbone

107
Q

Who do the ends of chromosomes get progressively shorter with each cell division?

A

RNA primer at the end of strand removed but cannot be replaced by DNA as DNA polymerase can only add to the 3’ end of an existing chain

108
Q

What is a telomere and its function?

A

A region of repetitive nucleotide sequence at the end of each chromatid

Protects ends of chromosomes by preventing loss of genes near the end

109
Q

Describe the process of transcription

A

Transcription - mRNA synthesis

RNA polymerase pries DNA helix apart. Unlike DNA polymerase, it does not need a primer to begin building RNA

RNA polymerase binds to a promoter (nucleotide sequence) and initiates RNA synthesis at start point within promoter

RNA joins complimentary nucleotides and builds RNA in a 5’ to 3’ direction (nucleotides added to 3’ end)

RNA molecule “peels away” from the template DNA, transcribed DNA returns to double helix structure

In bacteria: terminator sequence causes RNA polymerase to detach and release transcript

In eukaryotes: RNA polymerase transcribes a sequence known as the polyadenylation signal sequence (AAUAAA in pre-mRNA) which is automatically bound by certain proteins in the nucleus which cut it free from the RNA polymerase, releasing the pre-mRNA

110
Q

Pre-mRNA modification (RNA processing) only occurs in _____ cells

A

Eukaryotic

111
Q

What occurs during pre-mRNA modification?

A

5’ end receives 5’ cap (modified guanine)

3’ end receives poly-A tail (50-200 adenine nucleotides)

Introns spliced out from pre-mRNA strand and remaining exams ligated together to form mature mRNA

112
Q

What is the purpose of the 5’ cap and poly-A tail?

A

They facilitate export of mRNA from the nucleus and prevent degradation by hydrolytic enzymes as well as helping ribosomes attach to the 5’ end of the mRNA

113
Q

What is the components and function & process of the spliceosome?

A

Spliceosomes = proteins + small RNAs (snRNPs, small nuclear ribonucleoproteins)

SnRNA (small nuclear ribonucleicacid) pairs with bases in pre-mRNA intron (splice sites)

Spliceosome cuts pre-mRNA and releases intron for degradation

Spliceosome ligates exon end together - catalysed by snRNA

Releases mature mRNA

114
Q

What does an aminoacyl-tRNA synthetase do?

A

It attaches the correct amino acid to a tRNA molecule to form an aminoacyl-tRNA

aminoacyl-tRNA synthetase only fits a specific combination of tRNA and amino acid in its active area

115
Q

What is “wobble”?

A

Where base pairing between the 3rd nucleotide base of a codon and corresponding codon is more relaxed than the first two - results in flexible base pairing

116
Q

What are the three sites of a ribosome and what are their functions?

A

E site - exit site
P site - holds tRNA attached to existing polypeptide chain
A site - holds tRNA with to-be-added amino acid

117
Q

Describe the initiation step of translation

A

tRNA carrying methionine binds to small ribosomal subunit

5’ cap of mRNA binds to small subunit

tRNA “scans” mRNA until it finds a specific initiator (start codon) and then binds to it.

Large ribosomal subunit attaches and completes the translation initiation complex.

118
Q

Describe the translation step of translation

A

The anticodon of aminoacyl-tRNA pairs with its complementary codon in the A site

rRNA molecule of large subunit catalysed formation of peptide bond between new and growing polypeptide

Ribosome moves tRNAs into neighbouring sites

119
Q

Describe the termination step of translation

A

When ribosome reaches a stop codon, A site accepts a “release factor” which promotes the release of the polypeptide from tRNA

Polypeptide released via the exit tunnel, mRNA and ribosomal subunits dissociate

120
Q

What are polypeptides destined for secretion or the endomembrane system marked by?

A

They are marked with by a signal peptide which targets the protein to the ER

121
Q

What is a signal peptide and how does it work?

A

A signal peptide is a sequence of ~20 amino acids at/near the leading end (N terminus) of the polypeptide

It is recognised as it emerges by SRP (signal-recognition particle)

SRP “escorts” ribosome to a receptor protein build into the ER membrane

Polypeptide synthesis continues, growing chain crosses membrane into the ER lumen via signal pore

Signal peptide removed by an enzyme, units dissociate

122
Q

What is the difference between a ribosome and a polyribosome?

A

Polyribosomes are one mRNA strand with multiple ribosomes travelling along it, making chains.

123
Q

True or false: transcription and translation occur separately in bacteria

A

False: transcription and translation occur concurrently with one another in bacteria

124
Q

What is the genetic code

A

The means by which DNA and RNA molecules carry genetic information: codons, the triplet code which specifies amino acids

125
Q

What is meant by “the code is redundant”?

A

Most amino acids are specified by more than one codon

126
Q

What is the difference between spontaneous and induced mutations?

A

Spontaneous mutations occur due to random errors in the processes of transcription/translation

Induced mutations are a result of external agents damaging DNA

127
Q

What is excision repair? Describe the process.

A

Excision repair is the repairing of damaged/mismatched DNA by cutting out the affected area and replacing it with new nucleotides.

DNA polymerase proofreads DNA but may miss mismatched pairs.

Nuclear excuses (cuts out) damaged/mismatched section

Gap filled with appropriate nucleotides using undamaged strand as template by DNA polymerase

DNA ligase seals free ends of nucleotides to complete strand

128
Q

How do prokaryotes control gene expression?

A

Prokaryotes continually turn genes on and off in response to signals from their external and internal environments

129
Q

True or false: gene expression in eukaryotes is regulated at a single level.

A

False: gene expression in eukaryotes is regulated at many levels.

130
Q

How does chromatin modification (unpacking) influence gene expression?

A

Condensed chromatin needs to be loosed in order to allow access to DNA for transcription.

131
Q

How does transcription influence gene expression?

A

Transcription factors that facilitate RNA polymerase binding can also bind to regulatory sequences and stimulate/repress transcription of a gene

Regulating transcription is the most common way of controlling gene expression

132
Q

How does RNA processing affect gene expression?

A

Alternative splicing - different mRNA molecules produced from the same pre-mRNA = proteins of different size and function from the same pre-mRNA

133
Q

How does translation affect gene expression?

A

Translation is controlled by regulating factors which mediate initiation of translation

134
Q

How does degradation of RNA affect gene expression?

A

The lifespan of RNA in cytoplasm determines how long it can be used for protein synthesis

135
Q

How does protein processing and degradation affect gene expression?

A

Modification needed to produce a functional protein regulated

Protein trafficking to correct organelle regulated

Selective degradation influences the lifetime of a protein

136
Q

Non coding RNA can regulate gene expression by influencing: (3)

A

Chromatin packing

Translation

mRNA degradation

137
Q

How do prokaryotes control their metabolic processes? (2)

A

Adjust catalytic activities of preexisting enzymes

Adjust production of enzyme molecules by regulating expression of genes encoding enzymes

138
Q

How do prokaryotes adjust the catalytic activities of preexisting enzymes?

A

The product of the metabolic pathway inhibits the initial enzyme of the pathway which prevents production of final product - rapid response, feedback inhibition

139
Q

How do prokaryotes adjust production of enzyme molecules by regulating expression of genes encoding enzymes?

A

An abundance of products represses expression of genes encoding all enzymes in a metabolic pathway - long term response

140
Q

What is an operon?

A

Operator + promoter + controlled genes

Promoter: where RNA binds, controls transcription of all genes following it

Operator: found in promoter or between promoter and genes, controls access of RNA polymerase to genes

141
Q

What is the difference between negative and positive gene regulation?

A

Negative: repressive protein binds to operator, prevents expression

Positive: transcription factor or activator binds to promoter and enables RNA polymerase to initiate transcription

142
Q

Describe the process of negative regulation of the lac operon in the absence of lactose

A

Regulatory gene codes for repressor protein: lac I for lac repressor protein

The repressor protein binds to the operator and obstructs promoter

Transcription of the lac operon cannot occur, and beta galactosidase cannot occur

143
Q

Describe the process of negative regulation of the lac operon in the presence of lactose

A

Lactose acts as an induced

Lactose binds to lac repressor protein which induces a change in shape of the repressor

Repressor can no longer bind to the operator

Normal transcription of lac operon continues, 3 proteins produced

144
Q

When glucose levels are low, what happens to levels of cyclic AMP (cAMP)?

A

The levels of cAMP rise (accumulates)

145
Q

What is the function of cAMP?

A

cAMP binds to and activates the catabolite activator protein (CAP)

146
Q

Describe the process of positive gene regulation of the lac operon and describe how the results would differ in the presence of glucose/absence of glucose)

A

Active CAP binds to the promoter and facilitates binding of RNA polymerase to promoter, transcription can occur

Presence of lactose inhibits repressor protein (if no lactose, no lac operon transcription occurs)

In the presence of glucose, there are lower levels of cAMP = lower levels of activated CAP
No CAP = lower level of transcription, even if lactose is present

147
Q

Mutations in the lac operon may result in: (3)

A

The production of non-functional proteins

No transcription (e.g promoter mutation = no RNA polymerase binding)

Permanently active transcription

Biosci 101 (1 decks)

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