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Biology > 6.1.1 Cellular control > Flashcards

6.1.1 Cellular control Flashcards

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1
Q

What are the 3 components of a nucleotide?

A

Phosphate, deoxyribose sugar, base

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2
Q

Which bases are purines or pyrimidines?

A

A and G are purines.
T and C are pyrimidines.

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3
Q

What is a gene?

A

A sequence of bases, it codes for the production of amino acids which fold into proteins.

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4
Q

What is the fixed position of a gene called?

A

The locus.

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5
Q

What does it mean by the code being degenerate?

A

It means that more than one codon that codes for each amino acid.

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6
Q

What does it mean that the code is non-overlapping?

A

Each base is only read once.

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7
Q

What does it mean by the code being universal?

A

The same codon codes for the same amino acid in all organisms.

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8
Q

What is a mutation in a gene?

A

The change in the sequence of bases in DNA.

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9
Q

What are the 3 key types of mutation?

A

Substitution, insertion, deletion.

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10
Q

What are the features of a substitution mutation?

A

One nucleotide is substituted for another. EG ATC turns to AGC. The code is degenerate so sometimes this has no effect.
A change in the base sequence can cause a change in the amino acid sequence which can change the primary, secondary and tertiary structure of the protein.

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10
Q

What are the features of an insertion mutation?

A

An extra nucleotide may be added. Eg ACT may change to ACGT.

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11
Q

What are the features of a deletion mutation?

A

A nucleotide is removed.

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12
Q

What type of mutations cause a frame shift?

A

Deletion, insertion.

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13
Q

What is a frame shift?

A

It changes all of the codons after the mutation as it shifts the sequence of bases.
It causes all further amino acids to be changed including start/stop codons.
It results in a protein that will no longer perform it’s correct function in the cell.

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14
Q

What are the 3 effects a mutation can have?

A

Nonsense - the mutation results in one of the three stop codons.
Mis-sense - results in a different amino acid sequence being coded for, EG GTC changes to GTT.
Silent mutation - The same amino acid is coded for despite the mutation, could be the two codons code for the same amino acid or it occurred in non- coding region of DNA.

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15
Q

What are the 3 phenotypic effects mutations can have?

A

Neutral - Normal functioning proteins are still synthesised - phenotype of organism is unchanged.
Harmful - Proteins aren’t synthesised or are non-functional. Negatively impacts the phenotype.
Beneficial - Proteins synthesised with new and beneficial characteristics in the phenotype.

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16
Q

What effect can mutations have on enzymes?

A

Many proteins coded for by genes are enzymes which regulate metabolic pathways.
Mutations can cause the active site to be changed.
Enzyme activity can be slowed or stopped altogether.

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17
Q

What are mutagens?

A

They increase a mutation’s appearance.

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18
Q

What are the 3 mutagens?

A

Physical, chemical and biological mutagens.

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19
Q

What are chromosome mutations?
Where do they usually occur?
What can cause them?

A

They are mutations that affect whole chromosomes or number of chromosomes.
Usually occur in meiosis.
They can be caused by mutagens.

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20
Q

What effects do chromosome mutations have?

A

They can be silent but also lead to developmental difficulties.

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21
Q

What changes in chromosome structure can chromosome mutations have?

A

Deletion - section breaks off.
Duplication - section duplicated.
Translocation - section breaks off, and joins another homologous chromosome.
Inversion - section breaks off, is reversed, then joins back on.

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22
Q

What are housekeeping genes?

A

They are genes that code for enzymes necessary for reactions present in metabolic pathways like respiration.

23
Q

What are tissue specific genes?

A

Genes that code for hormones such as those required for growth and repair that are only required at certain times to carry out a short lived response.

24
Q

Why do genes need to be switched on and off?

A

Every cell with a nucleus has the entire genome of the organism. Not all genes in every cell need to be turned on.

25
Q

What is chromatin remodelling?

A

It is a simple form of regulation that ensures the proteins necessary for cell division are synthesised in time - before the division actually starts.
It also prevents the complex and energy intensive process of protein synthesis from occuring when cells are dividing.

26
Q

What is the difference between heterochromatin and euchromatin?

A

Heterochromatin - tightly wound DNA -> chromosomes are visible.
Euchromatin - loosely wound DNA.
When DNA is tightly wound, transcription of genes can’t take place.

27
Q

What causes chromatin remodelling?

A

Histone modification. DNA coils around histones because they are positively charged and DNA is negatively charged (due to the phosphate group)
Histones can be modified to increase or decrease the degree of packing / condensation.

28
Q

What are transcription factors?

A

Transcription factors are proteins which move in from the cytoplasm and bind to DNA.
They bind to the promoter region and this can either aid or inhibit the attachment of RNA polymerase to the DNA and therefore either activate or suppress transcription of the gene.

29
Q

What are transcription factors activated by?

A

Most TF are inactive and are activated by hormones/GFs (growth factors)

30
Q

Where are transcription factors found?

A

Some are in all cells, some are only in certain types.
Some are present at a particular stage of development.

31
Q

How much of the human genome encodes TFs?

A

About 8%.

32
Q

How are genes turned on?

A

Hormones activate TFs, therefore hormones activate genes.

33
Q

What is apoptosis?

A

Programmed cell death, a series of biochemical events leading to an orderly and tidy death.

34
Q

What should the rate of apoptosis equal?

A

The rate of cells produced by mitosis.
Too much cell loss leads to cell loss and degeneration.

35
Q

What do homeobox genes do?

A

They regulate mitosis and apoptosis in animals.

36
Q

What stimuli regulate expression of homeobox genes?

A

Internal and external stimuli.

37
Q

What are internal stimuli that regulate expression of homeobox genes?

A

Damage to DNA - detected in the cell cycle. Genes are expressed that cause the cell cycle to pause or trigger apoptosis.
Release of hormones.
Psychological stress.

38
Q

What are external stimuli that regulate expression of homeobox genes?

A

Change in light intensity, temperature.
Pathogen attack.
Lack of nutrients.
Drugs (thalidomide)

39
Q

What are signalling molecules of apoptosis?

A

The homeodomain protein can bind to genes coding for signalling molecules.
Many cell signals help to control apoptosis.
These signalling molecules include cytokines from cells of the immune system, hormones and nitric oxide.
Nitric oxide can induce apoptosis by causing proteins to be released from the cell into the cytoplasm which bind to apoptosis inhibitor proteins, allowing apoptosis to occur.

40
Q

What is the process of cells apoptosing?

A

Enzymes break down the cell cytoskeleton.
The cytoplasm becomes dense with tightly packed organelles.
The cell surface membrane changes and small protrusions called blebs form.
Chromatin condenses, the nuclear envelope breaks and DNA breaks into fragments.
The cell breaks into vesicles that are ingested by phagocytic cells so that cell debris doesn’t damage any other cells or tissues.

41
Q

What is the lac operon as a brief overview?

A

The regulation of the genes that code for enzymes to metabolise lactose.

42
Q

What is an operon?

A

A group of genes that are under control of the same regulatory mechanism and are expressed at the same time.
More common in prokaryotes than eukaryotes.

43
Q

What are the two key structural genes in the lac operon?

A

Lac Z and Lac Y.
Lac Z codes for B-galactosidase which hydrolyses lactose into glucose and galactose.
Lac Y codes for Lactose permease which facilitates lactose crossing the membrane into the cell.

44
Q

What is the regulatory gene in the lac operon?

A

Lac I - located near the operon and codes for a repressor protein that prevents transcription of the structural genes in the abscence of lactose.

45
Q

What are structural genes?

A

Genes that code for proteins.

46
Q

What are regulatory genes?

A

They code for a TF.

47
Q

What is post transcriptional level regulation?

A

The editing of primary mRNA and the removal of introns to produce mature mRNA.

48
Q

What is an intron?

A

A section of a gene that does not code for an amino acid.

49
Q

What is an exon?

A

Section of a gene that codes for amino acids.

50
Q

What is splicing of mRNA?

A

Removing the introns and sticking together the exons in primary-mRNA.
The intron is excised and the exons are then spliced together, mRNA may then leave the nucleus to the cytoplasm for the next stage of protein sysnthesis.

51
Q

What does cAMP (cyclic AMP) do?

A

It activates proteins by altering their 3D shape.
This could change the active of an enzyme to become more or less active.

52
Q

What is the upregulation of the lac operon?

A

RNA polymerase still only results in relatively slow transcription needing to be increased to produce the required quantity of enzymes to metabolise lactose effectively.
This is achieved by the binding of another protein cAMP receptor protein (CRP) to the promoter. CRP is only activated when cAMP is bound to it.
The binding of cAMP changes the shape of the CRP.
The transport of glucose into the cell decreased the levels of cAMp reducing the transcription of the genes responsible for metabolism of glucose.

53
Q

How does the lac operon turning genes off work when lactose is not present?

A

When there is no lactose around, the repressor protein binds to the operator region of DNA. RNA polymerase cannot bind to the promoter region and so the structural genes are not transcribed.

54
Q

How does the lac operon turning genes on when lactose is around work?

A

Lactose binds to the repressor on the promoter region and causes it to become inactive. RNA polymerase can now bind and read the genes coding for the enzymes needed to break down lactose.

55
Q
A

Biology (16 decks)

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