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Biology > Chapter 19 - Cellular Control > Flashcards

Chapter 19 - Cellular Control Flashcards

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1
Q

What is a gene mutation?

A
  • Random change in sequence of base pairs in DNA molecule resulting in altered polypeptide
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2
Q

What can be mutagenic?

A

tar, ionising radiation such as UV light, X-rays and gamma rays

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3
Q

What are the 2 main classes of DNA mutations?

A
  • Point mutation: one pair replaces another
  • Insertion/deletion mutation: one or more nucleotides are inserted or deleted from a length of DNA
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4
Q

What are the 3 types of substitution mutation?

A
  • Silent
  • Missense
  • Nonsense
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5
Q

Silent mutation

A
  • The mutation does not alter the amino acid sequence of the polypeptide
    (this is bc certain codons may code for the same amino acid as the genetic code is generate)
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6
Q

Missense mutation

A

-alters a single amino acid in polypeptide chain eg. sickle cell anaemia
- effect on protein produced
- change in tertiary structure + alters the shape

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7
Q

sickle cell anaemia

A
  • from a missense mutation on the 6th base triplet of the gene for the polypeptide chains of haemoglobin: valine, instead of glutamic acid, is inserted
  • results in deoxygenated haemoglobin crystallising within erythrocytes
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8
Q

Nonsense mutation

A

creates a premature stop codon
causes incompletion of polypeptide chain
affects tertiary structure and function
eg. cystic fibrosis

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9
Q

What are the 3 main ways that a mutation in the DNA base sequence can occur?

A

Insertion
Deletion
Substitution

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10
Q

Insertion mutation

A

mutation that occurs when a nucleotide is randomly inserted into the DNA sequence
- changes the amino acid that would have been coded for by the original base triplet, as it creates a new, different triplet of bases
- insertion mutation also has a knock-on effect by changing the triplets further on in the DNA sequence (frameshift mutation)
- may change the amino acid sequence produced from this gene + the ability of the polypeptide to function

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11
Q

Frameshift mutation

A
  • insertion mutation has a knock-on effect by changing the triplets further on in the DNA sequence
  • changes the amino acid sequence produced from this gene
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12
Q

Deletion of nucleotides

A
  • mutation that occurs when a nucleotide is randomly deleted from the DNA sequence
  • changes the amino acid that would have been coded for
  • knock- on effect by changing the groups of 3 bases further on in the DNA sequence (frameshift mutation)
  • may change the amino acid sequence produced + ability of the polypeptide to function
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13
Q

Substitution of nucleotides

A

mutation that occurs when a base in the DNA sequence is randomly swapped for a different base.

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14
Q

Beneficial mutation

A
  • a small number of mutations result in a significantly altered polypeptide with a diff shape
  • may result in an altered characteristic in an organism that causes beneficial effects for the organism.
  • alter the ability of the protein to perform its function
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15
Q

Harmful Mutation

A

By altering a polypeptide, some mutations can lead to altered characteristic in an organism that causes harmful effects for the organism

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16
Q

Neutral mutations

A

offer no selective advantage/disadvantage to the individual organism

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17
Q

Why could neutral mutations occur? (3)

A
  • mutation doesn’t alter the polypeptide
  • only alters the polypeptide slightly so that structure/ function is not changed
  • mutation alters the structure/function of the polypeptide but the resulting difference in the characteristic of the organism provides no ad/dis to the organism.
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18
Q

Nucleus

A

same genes
HOWEVER NOT EVERY GENE IS EXPRESSED
not all these genes are expressed all the time

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19
Q

Regulatory mechanisms

A

-several mechanisms that exist within cells to make sure the correct genes are expressed in the correct cell
- control which genes are expressed at diff points in time

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20
Q

What are the 3 main types of regulatory mechanisms?

A

regulation at the transcriptional level (reg. mechs that occur…)
regulation at the post-transcriptional level
regulation at the post-translational level

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21
Q

What are regulatory mechanisms controlled by?

A

many diff regulatory genes

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22
Q

Structural gene

A

codes for a protein that has a function within a cell eg. enzyme

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23
Q

Regulatory gene

A

code for proteins that control the expression of structural genes
-control structural genes + their levels of protein production

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24
Q

What is the lac operon an example of?

A

a regulatory mechanism at the transcriptional level

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25
Q

Lac operon

A

structural genes in prokaryotes form an operon
- lac operon controls the production of the enzyme lactase (also called β-galactosidase) + 2 other structural proteins
- Lactase breaks down the substrate lactose so that it can be used as an energy source in the bacterial cell
It is known as an inducible enzyme (only synthesised when lactose is present)
- helps prevent the bacteria from wasting energy and materials

26
Q

What is an operon?

A
  • A group or a cluster of genes that are under the control of the same regulatory mechanism + expressed at the same time
27
Q

What order are components of lac operon found in?

A

promoter for structural genes
operator
structural gene lacZ that codes for lactase
structural gene lacY that codes for permease (allows lactose into the cell)
structural gene lacA that codes for transacetylase

28
Q

What are the 3 enzymes the lac operon codes for?

A
  • B-galactosidase, lactose permease and transacetylase
29
Q

What happens to the 3 enzymes?

A
  • transcribed onto a long molecule of mRNA
30
Q

What is the role of cyclic AMP?

A
  • binding of RNA polymerase results in a slow rate of transcription that needed to be increased to produce the required quantity of enzymes to metabolise lactose efficiently
  • this is achieved by binding of cAMP receptor protein, which is only possible when CRP is bound to cAMP
31
Q

3 effects of gene mutations on polypeptides

A
  • beneficial mutation
  • harmful mutation
  • neutral mutation
32
Q

Lac repressor protein

A
  • has two binding sites that allow it to bind to the operator in the lac operon and also to lactose (the effector molecule)
  • When it binds to the operator it prevents the transcription of the structural genes as RNA polymerase cannot attach to the promoter
  • When it binds to lactose the shape of the repressor protein distorts and it can no longer bind to the operator
33
Q

When lactose is absent

A
  • regulatory gene is transcribed and translated to produce lac repressor protein
  • lac repressor protein binds to the operator region upstream of lacZ
  • due to the presence of the repressor protein, RNA polymerase is unable to bind to the promoter region
  • transcription of the structural genes does not take place
  • No lactase enzyme is synthesised
34
Q

When lactose is present

A
  • uptake of lactose by the bacterium
  • lactose binds to the second binding site on the repressor protein, distorting its shape so that it cannot bind to the operator site
  • RNA polymerase is then able to bind to the promoter region + transcription takes place
  • mRNA from all three structural genes is translated
  • lactase is produced and lactose can be broken down and used for energy by the bacterium
35
Q

control of repressible enzymes

A
  • effector molecule binds to a repressor protein produced by a regulatory gene. However this binding actually helps the repressor bind to the operator region and prevent transcription of the structural gene
  • opposite of the lac operon: when there is less of the effector molecule, the repressor protein cannot bind to the operator region and transcription of the structural genes goes ahead, meaning the enzyme is produced.
36
Q

Transcription factors

A

Eukaryotes can use transcription factors to control gene expression via RNA poly
proteins that bind to specific regions of DNA to control the transcription of genes

37
Q

How transcription factors work

A

Some transcription factors bind to the promoter region of a gene
- bind either allows or prevents transcription of gene from taking place
- presence of a transcription factor will either increase or decrease the rate of transcription of a gene

38
Q

Gene control: oestrogen

A
  • lipid-soluble molecule + therefore diffuses through the plasma membrane of cells
  • moves to the nucleus + binds to an oestrogen receptor
  • these receptors are actually transcription factors that are able to initiate transcription for many different genes by binding to their promoter regions
  • Once bound, oestrogen causes a change in the shape of the receptor
  • As a result, the receptor moves away from the protein complex it is normally attached to + binds to the promoter region of one of its target genes
  • this allows RNA polymerase to bind and to begin transcribing that gene
39
Q

Gene control: gibberellin

A
  • Gibberellin is a hormone found in plants (e.g. wheat and barley) that controls seed germination by stimulating the synthesis of the enzyme amylase
  • does this by influencing transcription of the amylase gene
  • When gibberellin is applied to a germinating seed there is an increased amount of the mRNA for amylase present
40
Q

Mechanism of gene control: gibberellin

A

The breakdown of DELLA protein by gibberellin is necessary for the synthesis of amylase
components involved:
Repressor protein DELLA, Transcription factor PIF

DELLA protein is bound to PIF, preventing it from binding to the promoter of the amylase gene so no transcription can occur
Gibberellin binds to a gibberellin receptor and enzyme which starts the breakdown of DELLA
PIF is no longer bound to DELLA protein and so it binds to the promoter of the amylase gene
Transcription of amylase gene begins
Amylase is produced

41
Q

Exons and introns

A
  • coding sequences are called exons + these are the sequences that will eventually be translated into the amino acids that will form the final polypeptide
  • non-coding sequences are called introns and are not translated (they do not code for any amino acids)
  • When transcription of a gene occurs, both the exons and introns are transcribed
42
Q

mRNA modification

A

As the introns are not to be translated, they must be removed from the pre-mRNA molecule
- exons are then all fused together to form a continuous mRNA molecule called mature mRNA that is ready to be translated (splicing)
- Splicing ensures that only the coding sections of mRNA are used to form proteins by translation (if any introns were included in the mature mRNA, the resulting protein would not be formed properly and may not function as it should)

43
Q

Control at the post-translational level

A

After polypeptides are formed by translation, they undergo modifications in the Golgi apparatus or in the cytosol
Some polypeptides may then require activation by cyclic AMP (cAMP)
cAMP is derived from ATP and is formed by the action of the enzyme adenyl cyclase

44
Q

Homeodomain sequence

A
  • the sequence of homeobox genes
  • homeodomain is sequenced, transcribed and translated to form a protein called Helix - turn - helix protein that fits with DNA
45
Q

Helix turn Helix protein

A
  • it is alpha helix with normal shape and then it turns and then back to normal shape
46
Q

Homeobox gene

A
  • forms a homeodomain sequence that regulates transcription
  • responsible for the genetic control of the development of limbs and organs in different organisms at correct time and location
  • they help to form the basic pattern of the body eg. control polarity of organism (which end is tail or head) segmentation of organisms (insects have segments in their main body)
  • seen as ‘master genes’ that control which genes function at different stages of development
  • maintained by natural selection and won’t change - e.g no use of tail so gene turned off and tail won’t grow in womb
47
Q

Hox genes

A

subset of homeobox genes but only in animals
- determine body plans of anterior-posterior (head to tail)
- Vertebrates have four Hox clusters (each containing 9-11 Hox genes), which are found on different chromosomes
- linear order to the Hox genes in each Hox cluster + this order is directly related to the order of the regions of the body that they affect

48
Q

EvoDevo

A
  • the field of study involving hox genes and body plans from an embryo to full adult
49
Q

Hox Clusters

A

Group of hox genes

50
Q

e.g Fruit Fly

A
  • the hox genes of a fruit fly was mapped and colour coded
  • different hox genes of diff parts of fruit fly was turned on and off to see what happens
  • e.g legs out the head etc
  • advantages - not much ethical problems of using fruit fly, cheap, they make lots of offspring
51
Q

transcription factors of transcription factors

A

mRNA in cytoplasm of egg made from ‘gap genes’. They reulate the homeobox genes.

52
Q

Thalidomide

A
  • initially used for insomnia back then
  • doctors used it on pregnant insomniacs and realised it stops morning sickness
  • kept prescribing
  • caused limb abnormalities due to prevention of normal expression of hox genes in fetus
  • inhibits some homeobox genes
53
Q

Retonic acid - Vitamin A

A
  • also a transcription factor
  • similar to thalidomide
  • should be avoiding during pregnancy and told to avoid foods with it
54
Q

The control of mitosis and apoptosis

A

Mitosis is controlled by various different genes that are categorised into two distinct groups:
Proto-oncogenes are genes that stimulate cell division
Tumour-suppressor genes are genes that reduce cell division
Tumour-suppressor genes can also stimulate apoptosis in cells with damaged DNA that cannot be repaired
This protects the body as it ensures that any cells that are genetically damaged (and that could, therefore, lead to cancer) are destroyed

55
Q

Stage 1 of apoptosis

A
  • enzyms break down cytoskeleton
  • cytoplasm becomes dense with organelles tightly packed
56
Q

Stage 2 of apoptosis

A
  • cell surface membrane changes and small bits called blebs form
  • Chromatin condenses
  • Nuclear membrane breaks and the DNA breaks up into fragments
57
Q

Stage 3 of apoptosis

A
  • Cell breaks up into vesicles
  • Vesicles taken up by phagocytosis (phagocytes)
  • Cellular debris are disposed of and does not damage any cells or tissues
58
Q

The importance of mitosis and apoptosis in controlling body plan development

A
  • Apoptosis is important in development as, in some cases, some cells that are produced (by mitosis) earlier on in development may no longer be needed
  • so these cells are destroyed (by apoptosis) as part of the development of the organism
59
Q

What are the checkpoints in cell cycle controlled by?

A

cyclins and cyclin-dependent kinases (CDKs)
-> cyclins act as regulators
-> CDKs act as catalysts (once activated by cyclins)
eg. CDKs that have been activated by cyclins will catalyse the phosphorylation of particular target proteins, which can either activate or inactivate them
- ensures the cell cycle progresses from one stage to the next
-diff cyclins are produced at different stages of the cell cycle in response to internal molecular signals

60
Q

The genes that control the cell cycle and apoptosis are able to respond to:

A

Internal cell stimuli (e.g pH, enzymes)
External cell stimuli (e.g light, temp)

61
Q

Examples of internal cell stimuli

A

Internal factors that affect apoptosis and the cell cycle include:
Irreparable genetic damage
RNA decay
Internal biochemical changes that lead to cell changes or cellular injury (e.g. oxidative reactions)
Production of cyclin D

These factors can all initiate apoptosis in cells that are undergoing cell stress

62
Q

Examples of external cell stimuli

A

External factors that affect apoptosis and the cell cycle include:

  • presence of cell signalling molecules like cytokines from the immune system, hormones + growth factors
  • viruses + bacteria, harmful pollutants or ultraviolet light can affect the delicate balance of mitosis and apoptosis by damaging or destroying cells faster than they can be repaired or replaced

Cells often respond to such stressful stimuli by activating pathways to increase their chance of survival, or by initiating apoptosis
eg. a cell will often begin by defending itself and trying to recover from the stressful stimulus by counteracting any damage caused to it
but, if the stressful stimuli remain, cell death pathways are activated (i.e. apoptosis is initiated)

Biology (25 decks)

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