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Biology > 6.1 - Cellular control > Flashcards

6.1 - Cellular control Flashcards

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1
Q

What is a genome?

A

All the genetic material of an organism, including genes and non-coding DNA

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2
Q

What is a histone?

A

A protein DNA which has wrapped around to form a chromatin. This allows DNA to be more compactly packaged

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3
Q

What is a gene?

A

A section of DNA that codes for a polypeptide

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4
Q

What is transcription?

A

The process of copying DNA’s base sequence into mRNA

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5
Q

What is translation?

A

The process of using mRNA base sequences to produce a specific polypeptide chain

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6
Q

What is a mutation?

A

A change to the DNA code’s bases/nucleotides

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7
Q

What is a chromosomal mutation?

A

Mutations that affect the whole chromosome or a number of chromosomes within a cell

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8
Q

What are gene mutations?

A

Changes to the base sequence of genes in DNA

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9
Q

What is substitution? (Point mutation)

A

When one or more bases are swapped for others

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10
Q

What are the three sub-types of substitution?

A

1) Mis-sense
2) Nonsense
3) Silent

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11
Q

What is insertion?

A

When one or more bases are added into the sequence of the gene

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12
Q

What is deletion?

A

When one or more bases are removed from the sequence of the gene

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13
Q

What is a frameshift?

A
  • When every codon after the mutation is effected the protein will have a different sequence of amino acids and a different tertiary structure
  • This can change the function of the protein as well
  • This is caused by insertions and deletions
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14
Q

What is a mis-sense mutation?

A
  • Where a substitution causes a different amino acid to be coded for
  • This could affect the protein’s tertiary structure
  • This can stop the protein from doing its normal function
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15
Q

What is a nonsense mutation?

A
  • Where one base is substituted with another causing a stop codon to be created
  • This creates a truncated protein (A protein that has been stopped, resulting in it being too short)
  • This results in a protein which has a part missing from its tertiary structure
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16
Q

What is a silent mutation?

A

-Where a substitution occurs that has no effect on the amino acid coded for
-This is because the altered code could still code for the same amino acid, due to the degenerate nature of the code
(Different triplet code, still codes for the same amino acid)

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17
Q

What are chromosomal mutations?

A
  • Mutations that occur during meiosis that affect the whole chromosome/number of chromosomes within a cell
  • Chromosomal mutations normally lead to too many chromosomes being inherited
  • This can sometimes lead to polyploid offspring from meiosis
  • This happens when diploid gametes come together to form a 4n offspring that is polyploid
  • This would kill any mammal offspring however in plants, this mutation can occur and the plant can still survive
  • Orchid breeders often breed to make flowers that are polyploids as they look unique
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18
Q

What is translocation?

A

When a section of one chromosome breaks off and joins another non-homologous chromosome

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19
Q

What is inversion?

A

When a section of one chromosome breaks off, is reversed, and joins back to the chromosome

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20
Q

What is the purpose of the regulatory gene’s products?

A

It switches genes off and on

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21
Q

What is the purpose of the structural gene’s products?

A
  • Makes the enzyme

- E.g: Beta galactosidase or Lactose permease

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22
Q

What is the purpose of the lac operon?

A
  • The lac operon is usually found in bacterial cells
  • Its purpose is to regulate the expression of enzymes that break down lactose
  • The lac operon determines whether hydrolytic enzymes are needed for breaking down lactose if it is present
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23
Q

What occurs when glucose is not present for aerobic respiration in bacterial cells?

A
  • Lactose is used
  • The bacteria must produce proteins to transport the lactose inside the bacterial cell
  • This lactose must then be broken down by hydrolytic enzymes
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24
Q

What is the purpose of the regulatory gene?

A

To code for the repressor protein that switches genes on and off

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25
Q

What is the purpose of the promoter region?

A

The repressor protein aims to bind to the promoter region

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26
Q

What is the process of transcription when lactose is present?

A
  • Lactose binds to the repressor protein
  • The repressor protein changes shape
  • This stops the repressor protein from being able to bind to the operator
  • RNA polymerase can now bind to the promoter region and structural genes
  • The enzymes can then be transcribed to hydrolyse the lactose
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27
Q

What are introns?

A

Non-coding regions inside genes

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28
Q

What are exons?

A

Coding regions inside genes

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29
Q

What is splicing? (At a post-transcriptional level)

A
  • The process of removing the introns from mRNA to produce mature mRNA
  • Activated by cAMP which changes the shape of the protein causing splicing
30
Q

What is the functions of cAMP at a post-translational level?

A
  • cAMP activates the proteins inside the cell by altering their 3D structure
  • cAMP also activates protein kinases which then activates other proteins by catalysing the addition of a phosphate (phosphorylation)
  • cAMP may also activate enzymes so they can function properly
31
Q

When can mutations occur?

A
  • Mutations can occur spontaneously during replication as there is an error rate which is approximately 1 every 100,000 nucleotides
  • This mutation can only be passed on if it occurs in a germ cell (A cell that is going to go on to become a sperm or an egg cell)
  • If this mutation occurs in a different body cell then it could give rise to a disease such as cancer for example
32
Q

What can increase the chance of mutations?

A
  • Mutagenic agents increase the error rate which can cause mutations
  • Some example of mutagenic agents are:
  • UV light
  • Radiation
  • Certain chemicals
33
Q

What are carcinogenic agents?

A
  • Factors that can specifically cause mutations in genes that take part in the process of the cell cycle
  • These factors can lead to cancer
34
Q

Why is DNA described as a triplet code?

A

DNA is sometimes described as having a triplet code because 3 bases code for one amino acid in the polypeptide chain

35
Q

What does a missense mutation do the protein?

A
  • The triplet code is changed as one amino acid is substituted
  • This means a different codon and a different amino acid is inserted by the ribosome to make the polypeptide chain
  • This means that the proteins primary and secondary structure is changed (The tertiary structure can also be changed)
  • The protein may not be the right shape so the function of the protein could be altered
  • This could mean that, if the protein is an enzyme it is the wrong shape and it isn’t complimentary to the substrate
36
Q

What is a triplet nucleotide repeat?

A
  • When naturally occurring repeats of triplets, repeat too many times
  • This is seen in the protein “Huntingtin”
  • Huntingtin repeats the same triplet code 6-35 times, however if a triple nucleotide repeat mutation occurs, the code may repeat too many times (40-120 times)
  • This can result in a polypeptide chain that is too long, this means the tertiary structure can be affected as the code is too long to fold into the normal 3D structure for the protein
  • Instead of folding normally into the 3D structure, the mutated Huntingtins forms clumps of protein which can destroy or cause damage to the brain tissue
  • This can cause neurodegeneration (The brain slowly breaking down) that can eventually lead to death
37
Q

What does polyploidy mean?

A

-If an offspring is polyploidy it has an extra set of chromosomes (3n,4n etc) due to a mutation that has occurred in meiosis

38
Q

What does aneuploidy mean?

A
  • If an offspring is aneuploidy it has an extra single chromosome
  • For example if a person has three of chromosome 21 they have downs
39
Q

How is downs developed in an offspring?

A

-When an egg has two copies of chromosome 21 instead of one
[The egg should only contain one copy because gametes normally only have one of each chromosome]
-This happens in meiosis in metaphase 1, when the two parent chromosomes fail to split so they are forced to stay stuck together for the rest of meiosis
-This causes the gamete that is produced to have two copies of chromosome 21, the sperm cell then adds another copy so the offspring has three copies of chromosome 21 which leads to the development of downs
-The person will survive with downs but there are various health complications associated with the disorder, such as: Early death or heart failure etc

40
Q

Why do bacteria only produce the enzymes to break down lactose when it is present in the environment?

A
  • E. coli is a common bacteria that can metabolize the nutrients glucose and lactose
  • The bacteria synthesizes lactose, metabolizing the enzymes but only when lactose is present in the environment
  • This is beneficial for the bacteria as it means it doesn’t waste energy on producing enzymes that are not needed
41
Q

How does bacteria break down lactose?

A
  • The bacteria must produce two proteins:
  • Lactose permease, a membrane transport (Carrier) protein which helps to transport lactose into the cell
  • Beta galactosidase, an enzyme that converts lactose into glucose and galactose
  • The genes that code for these proteins are close together in the bacteria’s circular loop of DNA, these genes are called an operon as they are close together and they operate together
  • The regulation of the operon is what affects the production of the two proteins to break down lactose
42
Q

What is the structure of the operon?

A

-The operon is made up of many genes that operate together in close proximity to each other:
-P = The promoter region
-O = The operator region
[The P and O regions are responsible for turning the operon on and off]
-Z = Structural gene
-Y = Structural gene
[The two structural genes get converted into the proteins to break down the lactose]

-To the left of the operon is the regulatory gene:
-I = Inhibitor (Regulatory gene)
[The regulatory gene normally codes for the repressor protein to be transcribed]
-The repressor protein binds to the DNA on the operator region

43
Q

What happens when there is no lactose present?

A

-When there is no lactose present, the repressor protein binds to the operator region of the bacterial DNA
[This also blocks the promoter region]
-The repressor protein blocks the RNA polymerase from being able to bind to the promoter region
-The RNA polymerase would normally transcribe the genes to make mRNA
-This means no proteins are made from the structural genes so resources are saved

44
Q

What happens when lactose is present?

A
  • If a molecule of lactose is detected, it binds to the repressor protein
  • This causes the repressor protein to have a conformational change of shape, this causes it to unbind from the operator region
  • The RNA polymerase can then bind to the promoter region, structural genes can then be transcribed and translated
  • This produces Beta galactosidase and Lactose permease
  • Lactose can then be taken into the cell and broken down by the enzymes
45
Q

Which structural genes code for Beta galactosidase and Lactose permease?

A
  • LacZ codes for Beta galactosidase

- LacY codes for Lactose permease

46
Q

How does Beta galactosidase break down lactose?

A

-Beta galactosidase breaks down lactose into beta galactose and glucose

47
Q

What is the purpose of Lactose permease?

A

-Lactose permease is a carrier protein that allows lactose to enter the cell so it can be broken down by beta galactosidase

48
Q

How is the control of transcription different in eukaryotes?

A
  • Eukaryotes have a nucleus

- Transcription is turned on/off by transcription factors

49
Q

What are transcription factors?

A
  • Transcription factors are DNA binding proteins
  • The proteins can bind to promoters to allow the DNA to be transcribed into mRNA
  • The proteins can also bind to promoters to block the DNA from being transcribed into mRNA
  • 8% of human genes are transcription factors
50
Q

How are humans able to have such a small number of genes compared to other organisms such as plants?

A
  • Humans were initially predicted to have 100,000 genes but when the genome was sequenced it was found that humans only had 30,000, this is less than some plants
  • Humans are able to have a relatively low number of genes as they are good at regulating the switching on/off of genes due to transcription factors
51
Q

How do transcription factors work to regulate transcription?

A
  • Transcription can only work if the transcription factors and the RNA polymerase can get to the DNA, to the gene that needs to be transcribed
  • Before a gene can be transcribed, the chromatin (where the DNA is packed) has to be in the right conformational shape
52
Q

What is chromatin?

A

-DNA tightly wrapped around histone proteins

53
Q

What are histones?

A
  • A protein which DNA tightly wraps around to form a chromatin
  • This allows the DNA to be more compactly packaged
54
Q

How can DNA packaging affect transcription?

A
  • The studies into how DNA packaging can affect access into the DNA is part of research to do with epigenetics
  • If DNA is tightly packaged around histone proteins transcription doesn’t occur
  • This is because the enzymes involved with transcription can’t actually access the DNA
  • If the DNA is loosely packaged then transcription can occur
55
Q

How can the DNA packaging be controlled in order to regulate transcription?

A
  • By adding or removing chemical groups, the cell can regulate how tightly packaged the histone proteins are
  • If they are too tight transcription will not occur
  • If they are loose, transcription can occur
56
Q

What is epigenetics?

A

-How genes can be switched on and off (Semi-permanently) to control cell differentiation

57
Q

What is DNA methylation?

A
  • When cytosine c is methylated a methyl group is added to it
  • The methyl group packs the DNA tightly, this means that if genes are methylated they are less likely to be transcribed
  • Methylation is permanently/semi-permanently turning genes off
58
Q

How can acetyl groups affect the control of transcription?

A
  • Acetyl groups can be added to or removed from histone proteins
  • Acetylation is the adding of acetyl groups, this unwinds DNA
  • If acetyl groups are removed then DNA is packed more tightly
59
Q

What is post-transcriptional control of gene expression?

A

-Post-transcriptional control is the splicing of the genetic code to remove introns

60
Q

What are introns?

A

-Introns are non-coding parts of the DNA, they do not code for amino acids that make up the protein

61
Q

What are exons?

A

-Exons are coding parts of the DNA, they code for amino acids that do make up the protein

62
Q

What is the process of the splicing of the genetic code?

A
  • Transcription occurs to create primary RNA
  • The primary RNA must now be processed (Spliced) to remove introns and produce mature mRNA
  • The spliceosome splices out the introns to make mature mRNA
  • This type of controlling genetic expression allows one gene to be able to code for multiple proteins
  • As genes have multiple exons, the way that the gene is spliced can affect the protein that is coded for
  • By removing different variations of the exons it means that a gene can code for various different proteins, this is called differential splicing
63
Q

What factors can affect the control of translation?

A
  • The stability of mRNA can be manipulated to control the rates of translation
  • The number of ribosomes would affect the rates of translation as more ribosomes would increase the translation rate so more amino acids will be made
64
Q

What is post-translational modification?

A

-An inactive form of the protein is made so that it can be used when it is activated

65
Q

How can proteins be activated in post-translational modification?

A
  • Activation of a protein occurs via phosphorylation (The adding of a phosphate group) this would switch on the protein
  • Adenyl cyclase is responsible for activating enzymes as it makes cAMP which then activates lots of other enzymes by causing their phosphorylation
  • Partial digestion of a protein can also be used to activate proteins, this occurs when an inactive protein is partially digested to form an active version of the enzyme
  • For example:
  • The inactive protein, trypsinogen is converted to the active protein trypsin
  • The inactive protein fibrinogen, which is soluble in the plasma is converted to fibrin which is insoluble in the plasma as it clumps together to form fibres that form part of a clot
66
Q

What are hox genes?

A
  • Hox genes work as transcription factors that control the development of body plans
  • Hox genes contain a homeobox sequence
  • Hox genes are also extremely highly conserved, as they are present in so many organisms, this means that transferring hox genes from one organism to another would be successful as hox genes are present in most animals (They are relatively universal among animals)
  • They occur in clusters
  • Flies have 1 cluster while humans have 4
  • This means that humans are able to build more complex body plans
  • The sequence of the genes on a chromosome is the same as the sequence of body parts in an organism
  • Changing the sequence of the genes can alter the body plan of the organism, this is why hox genes are referred to as master control genes
67
Q

What is a homeobox sequence?

A
  • All hox genes have a homeobox sequence however homeobox sequence don’t only code for hox genes
  • A homeobox sequence appears many times in the genome of a fruit fly
  • The homeobox sequence consists of a 180 base pair stretch of DNA which codes for a 60 amino acid protein
  • The homeobox protein forms a 3D tertiary structure called a helix turn helix shape which is a DNA binding domain
68
Q

Why are hox genes referred to as “master control genes”?

A
  • Hox genes are able to change the body plan of organisms based off of their gene sequence
  • Hox genes are able to control the body plan of organisms as they have control of various different processes and parts of the organism such as:
  • They can turn other genes off/on
  • They can regulate the cell cycle to make cells divide more quickly or more slowly to control the rate of growth
  • They can control apoptosis to cause programmed cell death
  • They can control gene expression
69
Q

What is apoptosis?

A
  • Programmed cell death
  • An example of this is in a hand of a developing embryo, the hand is first formed as a solid shape of cell but after the bones of the fingers have formed the cells in between each finger must be programmed to die so each individual finger can move freely
70
Q

How can apoptosis be triggered?

A
  • Intracellular signals can trigger apoptosis, for example: Cells with DNA damage can cause a signal to trigger apoptosis to kill any DNA that has been damaged
  • This is beneficial as the cells that are damaged could become cancerous and harm the rest of the body, so it is beneficial for the damaged cells detect their own damage so that they go through programmed cell death and kill themselves
  • Apoptosis can also be triggered if a mitosis checkpoint is failed
  • Extracellular signals can signal apoptosis such as T killer cells can detect if a cell is infected with a virus they will then bind to the cell and signal to phagocytes that it must be killed
71
Q

What is the process of apoptosis?

A

-A cell is signalled to undergo apoptosis
-The cytoskeleton breaks down so the cell looses shape
[The caspase enzyme is activated which causes a caspase cascade which digests the cell from the inside
-The chromatin in the nucleus condense
-The cell membrane folds in it itself, (Blebs are formed)
-The cell eventually blebs so much that it breaks into vesicles
-The nucleus breaks into fragments
-The vesicles and fragments are engulfed by phagocytosis

72
Q

Why must apoptosis and mitosis rates be regulated?

A
  • If apoptosis rates are too high this can lead to cell loss and degeneration
  • For example: Alzheimer’s is caused by apoptosis of brain cells
  • If apoptosis rates are too low this can lead to the formation/development of a tumour
  • If a cell is so damaged that its apoptosis mechanisms are not working, medication can be taken to restart the natural apoptosis process within tumours so then they can undergo apoptosis and kill themselves

Biology (23 decks)

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