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Biology Alevel > Cellular Control > Flashcards

Cellular Control Flashcards

1
Q

Gene mutation?

A

Change in the sequence of base pairs in a DNA molecule that may result in an altered polypeptide

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2
Q

What are mutagens?

A

Factors that can increase probability of a mutation occurring
E.g
Ionising radiation - X-rays break DNA strands which are altered in repair process
Deaminating chemicals - alter chemical structure of bases (convert one base to another)
Methyl/ethyl group added to bases - lead to incorrect base pairing
Viruses - insert section of viral DNA into DNA of cells

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3
Q

Why do most mutations have no effect on us?

A

Most don’t alter polypeptide/alter it very slightly so structure/function doesn’t change
- bc the genetic code is degenerate - several triplets code for same amino acid

  • many mutations occur in non-coding sections of DNA so have no effect on amino acid sequence
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4
Q

3 ways a mutation can occur?

A

Insertion of on/more nucleotides
Deletion of one/more nucleotides
Substitution of one/more nucleotides

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5
Q

How are insertions harmful?

A

Nucleotide randomly inserted into DNA sequence
Creates different triplet of bases - changes amino acid that would’ve been coded for
- also changes triplets further on in DNA sequence - FRAMESHIFT MUTATION

Dramatic change in amino acid sequence therefore ability of polypeptide to function

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6
Q

How are deletions harmful?

A

Nucleotide randomly deleted from DNA sequence
- changes amino acid that would’ve been coded for
- causes FRAMESHIFT mutation

Dramatic change to amino acid sequence/ability for polypeptide to function

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7
Q

Why is a substitution mutation harmful?

A

When a base in DNA sequence randomly swapped for a different base
- only change that triplet (where mutation occurs) - changes only the amino acid coded for by that triplet

3 forms:
Silent
Missense
Nonsense

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8
Q

What are silent mutations?

A

Mutation wont alter amino acid sequence of the polypeptide (bc code is degenerate)

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9
Q

What are missense mutations?

A

Mutation alters a single amino acid in the polypeptide chain
(E.g sickle cell anaemia)

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10
Q

What are nonsense mutations?

A

Mutation creates a premature stop codon (signal for cell to stop translation of mRNA molecule into amino acid sequence)
- causes polypeptide chain produced to be incomplete/ affecting final protein structure and fucntion

E.g cystic fibrosis

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11
Q

What are beneficial mutations ?

A

Beneficial: alteration to polypeptide results in altered characteristic that causes beneficial effects for the organism
E.g mutation for lower production of melanin meant vitamin D was synthesised easier in lower sunlight intensities

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12
Q

What are harmful mutations?

A

Harmful: mutation leads to altered characteristic that has harmful effects on organism
E.g cystic fibrosis - deletion of 3 nucleotides in gene coding for CFTR protein

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13
Q

What are neutral mutations?

A

Offer no selective advantage/disadvantage to the organism BC:
- mutation only affect polypeptide slightly /does not alter it at all
- mutation alters polypeptide but difference in characteristic provides no advantage/disadvantage to them

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14
Q

What are regulatory mechanisms?

A

Mechanisms inside cells that make sure correct genes are expressed in the correct cell at the correct time

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15
Q

3 types of regulatory mechanisms?

A

Regulation at the transcriptional level (i.e. regulatory mechanisms that occur during transcription)
Regulation at the post-transcriptional level (i.e. regulatory mechanisms that occur after transcription)
Regulation at the post-translational level (i.e. regulatory mechanisms that occur after translation)

These mechanisms are controlled by regulatory genes

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16
Q

What are structural and regulatory genes?

A

Structural: codes for a protein that has a function within a cell
Regulatory: codes for proteins (or forms of RNA) that control the expression of structural genes

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17
Q

What is Lac Operon ?

A

Structural genes in prokaryotes form an operon —> group/cluster of genes that are controlled by same promoter
- lac operon is one of these
Controls production of lactase (aka β-galactosidase)/2 other structural proteins

18
Q

Why is lactase an inducible enzyme and how is this beneficial ?

A

It’s only synthesised when lactose is present
- prevent bacteria wasting energy /materials

19
Q

Structure of lac operon?

A

In the following order, it consists of:
PROMOTER for structural genes
Operator
Structural gene lacZ- Code for lactase
Structural gene lacY - code for permease (allow lactose into cell)
Structural gene lacA- code for transacetylase

Next to lac operon:
promoter for regulatory gene
regulatory gene lacl - codes for lac repressor protein

20
Q

How does lac repressor protein work ?

A

Has 2 binding sites so can bind to OPERATOR on lac operon AND lactose
If binds to operator: prevents transcription of structural genes , as RNA polymerase cannot attach to PROMOTER
If binds to lactose : shape of repressor protein distorts —> CANNOT BIND TO OPERATOR

21
Q

Genetic control of a inducible enzyme at the transcriptional level:
Process on lac operon when lactose is absent ?

A
  1. Regulatory gene is transcribed/translated to produce LAC REPRESSOR PROTEIN
  2. Lac repressor protein binds to operator
  3. Due to this, RNA polymerase cannot bind to promoter region
  4. Transcription of structural genes does not take place —> NO LACTASE SYNTHESISED
22
Q

Genetic control of an inducible enzyme at transcriptional level:
Process on lac operon when lactose is present?

A

When lactose present in the medium the bacterium is growing in:
1. Lactose taken up by bacterium
2. Lactose binds to 2nd binding site on repressor protein —> distort repressor’s shape —> cannot bind to operator site
3. RNA polymerase can bind to promoter region + TRANSCRIPTION of structural genes TAKES PLACE
4. MRNA from all 3 structural genes translated
LACTASE PRODUCED / lactose broken down and used for energy

23
Q

Process of genetic control for a repressible enzyme?

A

Opposite of the lac operon
Effector present: Effector molecule (like lactose) binds to repressor protein
BUT INSTEAD , helps repressor to bind to operator region —> prevent transcription of structural genes

Less/no effector present: repressor cannot bind to operator / TRANSCRIPTION GOES AHEAD - enzyme produced

24
Q

How do eukaryotes control gene expression?

A

Use TRANSCRIPTION FACTORS - proteins that bind to specific regions of DNA to control transcription of genes
- control which genes in cell are turned on/off

25
Q

How do transcription factors work?

A

Some bind to PROMOTER REGION (control expression of gene) of a gene
This binding either ALLOW OR PREVENT transcription of a gene

Presence of transcription factor will either increase/decrease rate of transcription of gene

26
Q

Example of gene control : oestrogen?

A
  1. Oestrogen diffuses through plasma membrane/into nucleus
  2. Oestrogen attaches to receptor (that contained within a protein Complex)
  3. Oestrogen receptor changes shape and LEAVES protein complex
  4. Oestrogen receptor now attaches to PROMOTOR REGION of target gene
  5. This allows RNA polymerase to bind to gene and BEGIN TRANSCRIBING GENE
27
Q

Why is RNA analysis important with regards to gene expression?

A

When cell expresses gene - RNA produced by transcription
- this RNA can be analysed —> can match RNA in cell to specific genes and see which genes are expressed in that cell

28
Q

What are exons and introns?

A

Exons : coding region of DNA - will eventually be translated into amino acids
Introns : non coding region of DNA

29
Q

What is ‘splicing’ in post transcriptional modification?

A

When transcription of gene occurs —> EXONS AND INTRONS are transcribed
So the mRNA formed contains exons/introns —> called primary RNA / pre-mRNA

Introns must be removed from pre-mRNA as introns shouldn’t be translated
Exons are all fused together to form continuous mRNA called MATURE MRNA - ready for translation
This process called is ‘splicing’

30
Q

What does splicing ensure and what happens if introns are included in mature mRNA ?

A

Ensure that only coding sections of mRNA are used to form proteins by translation
If introns included in mature mRNA __. Protein wont be formed properly/wont function properly

31
Q

What happens in post translational level of gene regulation?

A

Polypeptides formed by translation undergo MODIFICATIONS in Golgi apparatus or cytosol

Some polypeptides may need to be activated by cAMP (derived from ATP using adenyl cyclase enzyme)
- cAMP activates protein kinase A enzyme , which activates other PROTEINS (other enzymes)

32
Q

E.g of when cAMP is used to activate polypeptides?

A

When muscle cells require energy
CAMP activates glycogen phosphorylase —> converts glycogen to glucose

CAMP changes shape of glucose phosphorylase to expose its active site

33
Q

What is a Homeobox and homeobox gene?

A

Homeobox : DNA sequence that codes for a protein transcription factor
Homeobox gene : any gene that contains a Homeobox sequence

34
Q

Homeoeobox genes sequences of plants, animals and fungi are ____________?

A

Similar- all code for amino acids sequences that will form transcription factors
highly conserved - been maintained by natural selection and remain relatively unchanged when travelling back in evolutionary time

35
Q

What are Hox genes responsible for?

A
  • control polarity of organisms (which end develop into head/tail) - anterior-posterior axis
  • symmetry of body/no.body layer
  • control segmentation of organisms into distinct body parts
  • control development of body parts (wings/limbs) and what organs are present in each section of body
36
Q

What are hox genes?

A

Subset of homeobox genes, containing homeobox sequences essential for the correct positioning of body parts

Hox genes organised into groups —> HOX CLUSTERS
Vertebrates have 4 HOX CLUSTERS found on different chromosomes

37
Q

What is apoptosis and the processes leading to this?

A

Programmed cell death (of normally old cells)
Processed include;
1. DNA of cell becomes denser/more tightly packed
2. Nuclear envelope of cell’s nucleus breaks down/chromatin condenses
3. Vesicle forming that contain hydroltic enzymes
4. Phagocytes engulfing /digesting cell via phagocytosis

38
Q

Why is apoptosis important in controlling body plan development?

A

In development, some cells that are produced by mitosis early in development , are no longer needed
- so cells are destroyed for development of organism

39
Q

How do hox genes control development?

A

Homeobox sequences code for a part of the protein called the HOMEODOMAIN
- homeodomain binds to specific sites on DNA , enabling proteins to work as a transcription factor

-homeodomain binds to DNA at he start of developmental genes,activating or repressing transcription

40
Q

Examples of internal cell stimuli that genes (which control cell cycle/apoptosis) respond to?

A

Internal: irreparable genetic damage
RNA decay
Internal biochemical changes leading to cell changes or cellular injury
Production of cyclin D

These all INITIATE APOPTOSIS in cells

41
Q

Example of external stimuli that genes (which control apoptosis/cell cycle) respond to?

A
  • presence of cell signalling molecules (cytokines from immune system, hormones, growth factors)
  • Viruses/bacteria, harmful pollutants, UV- damage/destory cells faster than they can be replaced

Cells respond by activating pathways to increase chance of survival/ initiating apoptosis

42
Q

Why are fruit flies often used in studies of genes that control body plan?

A

Fewer ethical concerns
Low cost
Their Genetics/development well understood
Have rapid reproduction rate
Have Simple body plan
Their Mutations can studied with low power microscope

Biology Alevel (28 decks)

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