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OCR A A level Biology > Cellular control > Flashcards

Cellular control Flashcards

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1
Q

Although all cells in an organism share the same genes, why does the structure/function of diff. cells vary?

A

Some genes aren’t expressed- transcribed and used to make a functional protein

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2
Q

What levels can gene expression be controlled?

A

Transcriptional, post-transcriptional and post-translational

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3
Q

How is gene expression controlled at the transcriptional level?

A

By altering the rate of transcription of genes. This is controlled by transcription factors.

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4
Q

What are transcription factors?

A

proteins that bind to DNA and switch genes on or off by increasing/decreasing the rate of transcription

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5
Q

What are activators?

A

Factors that start transcription

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6
Q

What are repressors?

A

factors that stop transcription

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7
Q

What does the shape of a transcription factor determine?

A

Whether it can bind to DNA or not

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8
Q

What can alter the shape of transcription factors?

A

the binding of molecules like some hormones and sugars

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9
Q

Where do transcription factors bind to in eukaryotes?

A

specific DNA sites near the start of their target genes

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10
Q

Where do transcription factors bind to in prokaryotes?

A

operons

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11
Q

What is an operon and what does it consist of?

A

a section of DNA containing a cluster of structural genes that are all transcribed together, control element, and sometimes a regulatory gene

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12
Q

Structural genes- function

A

code for useful proteins like enzymes

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13
Q

What do control elements consist of?

A

a promoter and operator

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14
Q

What is a promoter?

A

a DNA sequence located before structural genes that RNA polymerase binds to

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15
Q

What is an operator?

A

a DNA sequence that transcription factors bind to

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16
Q

Regulatory gene- function

A

codes for an activator or repressor

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17
Q

What does E.coli respire instead of glucose?

A

lactose

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18
Q

What is the lac operon?

A

the operon that consists of the genes that produce the enzymes needed to respire lactose

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19
Q

Name the 3 structural genes on the lac operon

A

lacZ, lacY, and lacA

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20
Q

What do the 3 structural genes in the lac operon code for?

A

proteins that help E.coli digest lactose e.g. beta-galactosidase and lactose-permease.

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21
Q

Lactose isn’t present- E.coli

A

1- Regulatory gene (lacI) produces the lac repressor, which is a TF that binds to the operator when lactose isn’t present
2- This blocks transcription because RNA polymerase can’t bind to the promoter

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22
Q

Lactose is present- E.coli

A

1-Lactose binds to the repressor, changing its shape so it can’t bind to the operator site
2- RNA polymerase begins transcription of the structural genes

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23
Q

What are introns?

A

In eukaryotic cells, these are sections of DNA that don’t code for amino acids post-transcription.

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24
Q

What are exons?

A

In eukaryotic cells, these are sections of DNA that do code for amino acids post-transcription.

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25
Q

What happens to introns and exons DURING transcription?

A

they are copied into mRNA

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26
Q

What are primary mRNA transcripts?

A

mRNA strands that contain introns and exons

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27
Q

What happens during the post-transcriptional level control?

A

Introns are removed from primary mRNA transcripts by splicing. Exons are joined together to form mature mRNA. This takes place in the nucleus. The mature mRNA leaves the nucleus for translation.

28
Q

Why is protein activation needed at the post-translational level control?

A

some proteins still aren’t functional straight after being synthesised and need to be activated to work.

29
Q

What is protein activation controlled by?

A

hormones and sugars

30
Q

How do some molecules control protein activation?

A

binding o cell membranes and triggering the production of cAMP inside the cell

31
Q

What does cAMP do?

A

it activates proteins inside the cell by altering their 3D structure which could, for example, change an enzyme’s active site, making it more or less active

32
Q

Activation of PKA by cAMP

A

When cAMP isn’t bound, PKA’s 4 units are bound together and are inactive.
When cAMP binds. it changes the enzyme’s 3D structure, releasing the active subunits. PKA is now active.

33
Q

What is PKA?

A

an enzyme made of 4 subunits

34
Q

What is a body plan?

A

the general structure of an organism

35
Q

What controls the development of a body plan and how?

A

proteins- they help set up the basic body plan so that everything’s in the right place

36
Q

What are hox genes?

A

the genes that code fr the proteins that control the body plan development

37
Q

Hox genes- Drosophila body plan

A

2 hox gene clusters control the development. One controls the development of the head and anterior thorax and the other controls the posterior thorax and abdomen.

38
Q

What are homeobox sequences?

A

Regions on hox genes that are highly conserved- this means that they have changed very little during the evolution of diff. organisms that possess it

39
Q

What does the homeobox sequence code for?

A

a part of the protein called the homeodomain

40
Q

What does the homeodomain do?

A

it binds to specific sites on DNA, enabling the protein to work as a transcription factor. the proteins bind to DNA at the start of the developmental genes, activating or repressing transcription and so altering the production of proteins involved in the body plan development.

41
Q

What is apoptosis?

A

when some cells die and are broken down

42
Q

How is a cell broken down after apoptosis is triggered?

A

1- Enzymes inside the cell break down the cell components
2- The cell shrinks and begins to fragment
3- Phagocytes engulf and digest the cell fragments

43
Q

Briefly describe the roles of mitosis+differentiation as well as apoptosis in development

A

mitosis and differentiation create a bulk of body parts and apoptosis refines them by removing unwanted substances

44
Q

Hands and feet- apoptosis example

A

when they first develop in humans, their fingers and toes and attached. apoptosis separates them in the cells in the connecting tissue

45
Q

Tadpoles and frogs- apoptosis example

A

as tadpoles develop into frogs, their tail cells undergo apoptosis to be removed

46
Q

Nervous system- apoptosis example

A

when developing the NS, excess nerve cells are produced. those that aren’t needed undergo apoptosis.

47
Q

What happens to the genes that control mitosis and apoptosis during development?

A

they’re switched on and off in appropriate cells so some new cells are produced while some die. the correct body plan is developing.

48
Q

What can the genes that regulate mitosis and apoptosis do?

A

respond to internal and external stimuli

49
Q

What happens to body plan development if an internal stimulus like DNA damage is found?

A

If detected in the cell cycle, this can cause the expression of genes that cause the cycle to be paused and even trigger apoptosis

50
Q

What happens to body plan development if an external stimulus is detected?

A

An example is stress caused by a lack of nutrient availability. This can cause gene expression preventing cells from undergoing mitosis.
Another external stimulus could be a pathogen- this could cause gene expression that leads to apoptosis.

51
Q

What are changes to the base sequence of DNA called?

A

mutations

52
Q

What are the 3 types of mutations?

A

substitution, deletion and insertion

53
Q

Substitution mutation

A

one or more bases are swapped for another base`

54
Q

Deletion mutation

A

one or more bases are removed

55
Q

Insertion mutation

A

one or more bases are added

56
Q

What does a mutation in a gene affect of a protein?

A

It alters its primary structure which could affect its final 3D structure so it doesn’t work properly
It can also cause a protein to not be produced at al

57
Q

What is frameshift mutation?

A

When insertion or deletion occurs, the number of bases changes causing a shift in all the base triplets that follow. It changes the way the rest of the sequence is read.

58
Q

The earlier a frameshift mutation occurs…

A

the more amino acids affected and the greater the effect of the mutation on the protein

59
Q

Why do some mutations have a neutral effect?

A

1- it changes a base in a triplet but the amino acid the triplet codes for doesn’t change e.g. both TAT and TAc code for tyrosine
2- a different amino acid is coded for but it is chemically similar so functions the same way e.g. arginine (AGG) and lysine (ACG)
3- it codes for an amino acid not involved in the protein’s function

60
Q

How can some mutations have an effect on a protein’s function?

A

they make it more or less active

61
Q

If a protein function is affected by a mutation, what effect can it have on the whole organism?

A

beneficial or harmful

62
Q

Beneficial mutations

A

they have an advantageous effect on the organism e.g. increase their chances of survival. these are passed on to future generations by natural selection.

63
Q

Beneficial mutation- example

A

some bacterial enzymes break down certain antibiotics. mutations in the gene that codes for these enzymes could make them work on more antibiotics. this antibiotic resistance helps them to survive.

64
Q

Harmful mutations

A
  • They have a disadvantageous effect on an organism e.g. decrease their chances of survival
  • They can also affect whether or not a protein is produced.
65
Q

Harmful mutation- example (CF)

A

cystic fibrosis is caused by the deletion of 3 bases in the gene that codes for the CTFR protein. if the protein is mutated, it folds incorrectly and is broken down. this leads to excess mucus production, which affects the lungs of CF sufferers.

OCR A A level Biology (6 decks)

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