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Biology AQA A-Level > Chapter 20 > Flashcards

Chapter 20 Flashcards

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1
Q

What are the three consequences of a substitution mutation?

A
  1. The formation of one of the three stop codons marking the end of the polypeptide chain. This means the production of the polypetide would be stopped prematurely. The final protein would be different and could not perform it’s final function.
  2. The formation of a codon for a different amino acid, so a singe amino acid may be different. The protein may differ in shape and may not function properly.
  3. The formation of a different codon for the same amino acid. This is due to the genetic code being degenerate and so most amino acids have more than one codon. The mutation will have no effect on the polypeptide produced.
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2
Q

What is a frame shift and what consequence does it have?

A

The deletion of a base will produce a frame shift as the reading frame that conatins each three letters of the code has been shifted to the left by one letter. The gene will be read in the wrong three base group and the coded information will be different. As most triplets will be altered so will most of the amino acids they code for. The polypeptide they produce will be different and most likely lead to a non functioning protein, altering the phenotype.

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3
Q

What is an addition mutation?

A

An extra base is inserted into the sequence causing a frame shift to the right. If any multiple of three bases are added this frame shift will not happen however teh resulting polypeptide would still be different from one produced by a non mutant gene

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4
Q

What is a duplication mutation?

A

One or more bases are repeated causing a frame shift to the right.

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5
Q

What is an inversion mutation?

A

A group of bases are seperated from the base sequence and rejoin but in the inverse order.

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6
Q

What is a translocation mutation?

A

A group of bases become seperated from the DNA sequence on one chromosome and become inserted on another chromosome. This will often have a significant impact on gene expressions leading to an abnormal phenotype.

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7
Q

Name and describe two mutagenic agents?

A
  1. High energy ionising radiation such as alpha and beta particles as well as short wavelength radiation such as x rays and uv light. These can disrupt the structure of DNA
  2. Chemicals such as NO2 may directly alter the structure of DNA or interfere with transcription.
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8
Q

How can gene mutations arise?

A

They can arise spontaneously during DNA replication, these occur without any outside interferance. Typically around one per 100 000 genes per generation

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9
Q

What benefits do muations bring?

A

They produce the genetic diversity needed for natural selection and speciation.

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10
Q

How do chemical mutagenic agents cause damage?

A
  1. Can remove groups from a nucleotide such as Nitrous acid. It can remove NH2 from cytosine changing it to uracil.
  2. Can add groups to nucleotides such as benzopyrene found in tobacco smoke. It adds a group to guanine making itunable to pair with cytosine. When DNA polymerase reaches teh affected guanine it inserts another base.
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11
Q

What type of mutation is caused by benzopyrene?

A

Substitution gene mutation

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12
Q

How does ionising radiation cause damage to DNA?

A

They produce free radicals in cells which can alter the shape of bases in DNA so DNA polymerase cannot act on them

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13
Q

How does ultraviolet radiation cause damage to DNA?

A

Affects thymine in DNA causing it to form bonds with the nucleotides either side of it, disrupting DNA replication.

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14
Q

How does the position of a deletion mutation change the severity of effect it produces?

A

A delted base at the start of a DNA could alter every triplet in the sequence. A deleted base near the end is likely to have less conseuquences as less triplets will be impacted.

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15
Q

Why do differenciated cells appear diferent from one another?

A

The proteins that a cell produces are coded for by the genes that are expressed.

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16
Q

What is a totipotent stem cell?

A

Found in the early embryo and can differenciate into any type of cell.

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17
Q

What is the role of controlling factors?

A

To conserve energy by ensuring genes that are not required are not expressed.

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18
Q

How are genes prevented from expressing themselves?

A

By preventing transcription and thus preventing the production of mRNA.
By preventing translation

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19
Q

What are stem cells?

A

Undifferenciated dividing cells that occur in adult mammal tissues. They can replicate and replace themselves by the process of sel-renewal

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20
Q

What is an embryonic stem cell?

A

Come from embryos in the early stages development. They can develop into any type of cell in the early stages of development.

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21
Q

What are umbilical cord stem cells?

A

Derived from the umbilical cord blood, have a similar ability of adult stem cells.

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22
Q

What are placental stem cells?

A

Found in the placenta and develop into specific typesn of cells.

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23
Q

What are adult stem cells?

A

Found in the body of the fetus through to adult. Specific to a particular tissue or organ which they produce teh cells to maintain and repair tissue.

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24
Q

What is a pluripotent stem cell?

A

As divides and matures pluripotent cells are developed. They are found in embryos and can develop into almost any type of cell. Examples include embryonic stem cells and fetal stem cells.

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25
Q

What is a multipotent stem cell?

A

Found in adults and can differenciate into a limited number of specialised cells. Examples include adult and umbilical cord stem cells.

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26
Q

What is a unipotent stem cell?

A

Can only differenciate into a single type of cell. They are derived from multipotent stem cells and are made from adult tissue.

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27
Q

What is an induced pluripotent stem cell?

A

A type of pluripotent cell that is produced from unipotent stem cells.

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28
Q

How is an induced pluripotent stem cell manufactured?

A

A unipotent stem cell is genetically altered in a lab to make them acquire the characteristics of embryonic stem cells. To make them acquire new charcteristics, genes and transciptional factors are reactivated meaning they are expressed.

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29
Q

How can pluripotent stem cells be utilised within medicine?

A

They can be used to regrow tissues that have been damaged

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30
Q

Describe the process of in vitro cloning of embryonic stem cells?

A
  1. The early embryo is cultured in a nutrient medium
  2. The outer layer collapses and the inner cell mass is freed from the embryo.
  3. Chemicals
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31
Q

Describe the process of in vitro cloning of embryonic stem cells?

A
  1. The early embryo is cultured in a nutrient medium
  2. The outer layer collapses and the inner cell mass is freed from the embryo.
  3. Chemicals are added to break up the cell mass into smaller groups.
  4. Each smaller group grows a colony.
  5. Differenciation factors are added to colonies in seperate containers.
  6. The differenciated cells can then be transfered to damaged tissues.
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32
Q

Name four features of plant growth factors?

A
  1. They have wide effects on plant tissues
  2. The effects on a particular tissue depend upon the concentration of the growth factor.
  3. The same concentration affects different tissues in different ways
  4. The effect of one growth factor can be modified by the presence of another
33
Q

What are the ethical issues surrounding using human embryonic stem cells for research purposes?

A

Should a human embryo less than 14 days old be afforded the same rights as a fetus or adult?

34
Q

What name is given to cells with the ability to mature into any body cell?

A

Totipotency

35
Q

What is a transcriptional factor?

A

Specific molecules that moves from the cytoplasm into the nucleus and switches on a gene so transcription can begin

36
Q

How does a transcriptional factor function?

A
  • The transcriptional factor has a site that binds to a specific base sequence of the DNA in the nucleus.
  • This causes the region of DNA to begin transcription.
  • mRNA is produced and the information it carries is then translated into a polypeptide.
37
Q

What happens to transcriptional factors when a gene is not expressed?

A

The site on the transcriptional factor that binds to DNA is not active and so it cannot cause transcription and polypeptide synthesis.

38
Q

How does oestrogen stimulate the expression of a gene?

A
  1. Oestrogen is lipid soluble and so easily diffuses through the phospholipid portion of the cell surface membrane.
  2. Once inside the cytoplasm of the cell, oestrogen binds with a complementary transcriptional factor.
  3. Oestrogen then changes the shape of the DNA binding site on the transcriptional factor, activating it.
  4. The transcriptional factor can now enter the nucleus through a nuclear pore and bind to specific base sequences on DNA.
  5. The transcriptional factor with DNA stimuates the transcription of the gene that makes up the portion of DNA.
39
Q

What is the epigenome?

A

DNA and histones are covered in chemical tags, forming a second layer- the epigenome. The epigenome determines the shape of the DNA-histone complex.

40
Q

What is epigentic silencing?

A

When the epigenome keeps inactive genes tightly packed ensuring the cannot be read.

41
Q

Why is the epigenome flexible?

A

The chemical tags respond to environmental changes such as diet and stress and can cause the chemical tags to adjust expressing and silencing certain genes.

42
Q

What can environmental signals stimulate proteins to carry out?

A

It stimulates proteins to carry its message inside the cell ffrom where it is passed by a series of other proteins into the nucleus. Here the message passes to a specific sequence of bases on the DNA.
Once attached it can change:
the acetylation of histones leading to the activation or inhibtion of a gene.
the methylation of DNA by attracting enzymes that can add or remove methyl groups.

43
Q

Why does condensation of the DNA-histone (chromatin) complex inhibit transcription and how is it brought on?

A

It condenses the DNA-histone complex meaning it is not accesible by transcription factors, and thus cannot initiate the production of mRNA therefore inhibiting transcription.
Brought on by decreased acetylation of the histones or by methylation of DNA

44
Q

What is acetylation?

A

Where an acetyl group is transferred to a molecule. The donating acetyl group is acetylcoenzyme A.

45
Q

What is the consquence of decreased acetylation?

A
  • The positive charges on this histones are increased, raising their attraction to the phosphate groups on DNA.
  • The association between DNA and histones is stronger and the DNA is not accesible to transcription factors.
  • Thus the transcription factor cannot initiate mRNA production from DNA
46
Q

What is methylation?

A

The addition of a methyl group (CH3) to a molecule. This is the cytosine base in DNA

47
Q

What two ways does methylation prevent the transcription of DNA?

A
  1. Preventing the binding of transcriptional factors to DNA

2. Attracting proteins that condense the DNA- histone complex making the DNA inaccesible to transcription factors.

48
Q

What experiment links epigentics and inheritance?

A

In rats, femaleoffspring who recieve good care wen young respond better to stress later in life and nurture their own offspring better. Whereas female offspring receiving low qualtity care nurture thir offspring less well. Good maternal behaviour in rats therefore transmits epigenetic information onto their offsprings DNA without passing through an egg or sperm.

49
Q

How can epigenetics lead to disease?

A

Alterign any epigentic processes can cause abnormal activation or silencing of genes associated with disease.

50
Q

What did researchers discover in 1983?

A

Researchers found that diseased tissue taken from patients with colorectal cancer had less DNA methylation than normal tissue

51
Q

What abnormailty involving the promotor regions of cells occurs in the early stages of cancer?

A

The promotor regions of cells become highly methylated causing genes that should be expressed to switch off.

52
Q

Why must epigenetic therapy specifically target cancer cells?

A

If it was used on healthy cells the induced gene transcription would make them cancerous themselves.

53
Q

How can epigentics be used in diagnostic tests?

A

Can be used to identify levels of DNA methylation and histone acetylation at early stages of diseases such as arthritis, brain disorders and cancer.

54
Q

What is siRNA?

A

Small interfering RNA, it interferes with gene expression and is a product of larger double stranded RNA being split into smaller sections by an enzyme.

55
Q

What is siRNA’s effect on gene expression?

A

An enzyme cuts large

56
Q

What is siRNA’s effect on gene expression?

A
  1. An enzyme cuts large double stranded RNA into smaller siRNA.
  2. One of the two siRNA combines with an enzyme
  3. The siRNA molecule guides the enzyme to a mRNA molecules by complementary base pairing on a section of the mRNA molecule.
  4. The enzyme cuts mRNA into smaller sections and so cannot be translated into a polypeptide and the gene has been blocked.
57
Q

What are the main characteristics of benign tumours?

A

Can slowly grow to a large size.
Cells are well differenciated.
Can produce adhesion molecules making them stick together so they reamain within the tissue they arise.
Surrounded by a capsule of dense tissue so remain as a compact structure.
Not likely to be life threatening if the function of vital organs arent disrupted, having mostly localised effects on the body.
Can be removed by surgery alone and rarely reoccur.

58
Q

What are the main characteristics of malignant tumours?

A

Can grow rapidly to a large size.
Cell nucleus appears larger and appears darker to an abundance of DNA.
Cells become differenciated.
Do not produce adhesion molecules so mestastasis occurs, forming secondary tumours.
Grow finger like projections into the neighbouring tissue.
Have systemic effects and likely to be life threatening as tumour tissue replaces normal tissue.
Usually involves radio/chemotherapy along with surgery and frequently reoccur.

59
Q

What is a proto-oncogene?

A

They stimulate a cell to divide when growth factors attach to a protein receptor on it’s cell surface membrane.

60
Q

What happens if a proto-oncogene mutates?

A

It mutates into an oncogene and can become permanently activated either by:
A- The receptor protein on it’s cell surface membrane is permanently activated so cell division is induced in the absence of growth factors.
B- The oncogene may code for a growth factor that is then produced in excessive amounts, stimulating cell division.

61
Q

What is apoptosis?

A

The process of tumour surpressor genes slowing down cell divison, repairing mistakes in DNA and programmed cell death.

62
Q

What is the role of tumour supressor genes?

A

Maintains normal rates of cell division, preventing the formation of tumours.

63
Q

What happens if a tumour supressor gene becomes mutated?

A

It becomes inactivated

64
Q

What happens if a tumour supressor gene becomes mutated?

A

It becomes inactivated and thus stops inhibiting cell division so cells grow out of control.

65
Q

Give three names of a tumour supressor gene?

A

TP53, BRCA1, BRCA2.

66
Q

What happens when there is an abnormailty of the TP53?

A

The P53 protein is involved in the process of apoptosis when a cell is unable to reapir DNA. If the gene for P53 is not functioning correctly, cells with damged DNA continue to divide leading to cancer

67
Q

How does hypermethylation lead to cancer?

A
  1. Hypermethylation occurs in the promotor region of tumour surpressor genes.
  2. This leads to the tumour surpressor becoming inactivated
  3. Transcription of the promotor regions of tumour surpressor genes is therefore inhibited.
68
Q

How does hypermethylation lead to cancer?

A
  1. Hypermethylation occurs in the promotor region of tumour surpressor genes.
  2. This leads to the tumour surpressor becoming inactivated
  3. Transcription of the promotor regions of tumour surpressor genes is therefore inhibited and so is silenced.
  4. It’s inactivation leads to increased cell division and the formation of a tumour.
69
Q

Why does the menopause increase a womens chances of developing breast cancer?

A

Fat cells of the breast contain more oestrogen after the menopause, triggering breast cancer. Once the tumour has been formed it further increases oestrogen concentration increasign the development of the tumour. White blood cells are drawn to tumour also increasing oestrogen production.

70
Q

What is bioinformatics?

A

The science of collecting and analysing complex biological data. It uses computers to read, store and organise codes at a rapid rate. Also utilises algorithems

71
Q

What is WGS sequencing?

A

Whole genome shotgun sequencing can determine the complete DNA base sequence. It involves researchers cutting DNA into small easily sequenced sections and then using algorithems to align overlapping segments to assemble the genome

72
Q

What are SNPs?

A

Single nucleotide polymorphisms have been found in the process of ssequencing the human genome. SNPs are single base variations in the genome that are associated with disease.

73
Q

What is the proteome?

A

All the proteins produced in a given type of cell (cellular proteome) or organism (complete proteome) at a given time under specified conditions.

74
Q

What was the first bacteria to have it’s genome fully seuquenced?

A

Haemophilius influenza in 1995. It contains 1700 genes comprising 1.8 million bases.

75
Q

What is the human microbiome project?

A

The sequencing of thousands of prokaryotic and single celled eukaryotic organisms with the goal of helping cure disease and provide knowledge of genes.

76
Q

Why is determining the proteome of prokaryotes relatively easy?

A

The majority have one circular strand of DNA that is not associated with histones.
There are no non-coding sections of DNA

77
Q

Why would sequencing the DNA of plamodium falciparum be of use?

A

It causes malaria and so all 5300 genes of it’s 14 chromosomes has been sequenced to give insight into it’s metabolism and the proteins it produces. This will help to create a potential vaccine

78
Q

Why is it more difficult to determine the genome of more complex organims?

A

The genome contaisn many non-coding genes as well as others that have a role in regulating other genes. As few as 1.5 % of genes are thought to code for proteins.

79
Q

How would the knowledge of the proteome of a pathogen be useful?

A

Allows identification of the proteins that act as antigens on the surfaces of pathogens. These can be used to produce a vaccine against the disease they cause.

Biology AQA A-Level (18 decks)

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