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A LEVEL Biology > Chapter 19 Genetics Of Living Systems > Flashcards

Chapter 19 Genetics Of Living Systems Flashcards

1
Q

What is a mutation?

A

A change in the sequence of bases in DNA.

  • if the mutation occurs within a gene… protein synthesis can be disrupted.
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2
Q

Causes of a change in sequence? (3)

A

(1) Substitution

(2) Deletion

(3) Insertion

… of one or more nucleotides (or base pairs) within a gene.

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3
Q

What is it called when only one nucleotide is affected?

A

POINT mutation

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4
Q

What does the substitution of a single nucleotide do?

A

Changes the codon in which it occurs.

  • if new codon codes for diff amino acids
  • it leads to a change in the primary structure of the protein
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5
Q

What is the NATURE of the genetic code?

++ what does this mean?

A

DEGENERATE nature of the genetic code, may mean the new codon still codes for the same amino acids - same protein synthesised.

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6
Q

What does the position and involvement of the amino acids in the R group interactions determine?

A

Determines the impact of the new amino acid on the function of the protein.

(e.g.) for understanding
- if the protein is an enzyme
- and the amino acid plays a role in the active site
- a change may result in the protein no longer acting as an enzyme

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7
Q

What does insertion and deletion of a nucleotide(s) lead to?

A

Frameshift mutation

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8
Q

How is the triplet code read?

A

= reading FRAME

The triplet code means that sequences of bases are transcribed (or read) consecutively in non-overlapping groups of 3.

  • each group of 3 bases correspond to 1 amino acid
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9
Q

How does the addition/ deletion of a nucleotide(s) affect the reading frame?

A

Moves, or SHIFTS the reading frame of the sequence of bases.

Changes every successive codon from the point of mutation.

++ unless the no. of nucleotides changed is a multiple of 3
- corresponds to a full codon - reading frame is unchanged
- YET the protein formed is diff (affected) as a new codon and subsequently amino acid is added

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10
Q

What are the possible effects of mutations? (3)

A

(1) NO effect
- no effect on the phenotype of an organism
- normally functioning proteins are still synthesised

(2) Damaging
- the phenotype is affected in a - way
- proteins are no longer synthesised OR proteins synthesised are non-functional

(3) Beneficial
- rare
- protein synthesised results in a new and useful characteristic in the phenotype

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11
Q

How is the rate of mutations affected?

A

INCREASED by mutagens.

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12
Q

What is a mutagen?

A

A chemical, physical, or biological agent which causes mutations.

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13
Q

Loss of purine/ pyrimidine bases??

A

(depurination OR depyrimidination)

  • occurs spontaneously
  • absence of a base can lead to insertion (of an incorrect base)
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14
Q

Free radicals??

A

Free radicals - oxidising agents

  • affect the structures of nucleotides and also disrupt base pairing during DNA replication
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15
Q

Antioxidants??

A

known as ANTICARCINOGENS

  • negate the effects of free radicals
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16
Q

++ types of mutations?? (3)

A

(1) Silent mutations (neutral)
- occur in non-coding regions of DNA (introns)
- or code for the same amino acid due to the degenerate nature of genetic code

(2) Nonsense mutations
- result in a codon becoming a stop codon
- shortened protein is formed

(3) Missense mutations
- incorporation of an incorrect amino acid into the primary structure

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17
Q

Compare gene mutations vs. chromosome mutations?

A

Gene mutations occur in single genes of sections of DNA.

Chromosome mutations affect the whole chromosome or no. of chromosomes.

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18
Q

What are the 4 types of changes in chromosome structure?

A

(1) Deletion
- a section of chromosome breaks off and is lost within the cell

(2) Duplication
- sections duplicated on a chromosome

(3) Translocation
- section of 1 chromosome breaks off and joins another non-homologous chromosome

(4) Inversion
- a section of chromosomes breaks off, is reversed, and joined back on

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19
Q

What are ‘house-keeping’ genes?

A

Genes which code for enzymes (necessary for reactions) in metabolical pathways.

++ constantly required

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20
Q

What do ‘tissue-specific’ genes code for?

A

Protein based hormones (required for the growth and development of an organism) are only required by certain cells at certain times.

++ carry out a short-lived response

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21
Q

How are bacteria able to respond to changes within their environment?

A

Gene regulation

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22
Q

What is gene regulation?

A

Expressing genes only when the products are needed.

  • prevents vital resources from being wasted
  • required for cells to specialise and work in a coordinated way
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23
Q

How are genes regulated? (4)

A

(1) Transcriptional
- genes can be turned on/ off

(2) Post-transcriptional
- mRNA can be modified which regulates translation and the types of proteins produced

(3) Translational
- translation can be stopped/ started

(4) Post-translational
- proteins can be modified after synthesis - changes their functions

24
Q

What are the different mechanisms which can affect the transcription of genes? (3)

A

(1) Chromatin remodelling

(2) Lac operon

(3) Role of cyclic AMP

25
How is DNA packed into the nucleus of a cell?
DNA is a very long molecule and must be wound around proteins (histones). - results in a DNA/ protein complex = CHROMATIN
26
What are the 2 types of chromatin?
(1) Heterochromatin - tightly wound - chromosomes visible during cell division (2) Euchromatin - loosely wound - present during interphase
27
When is transcription of genes NOT possible?
When DNA is tightly wound - heterochromatin. - RNA polymerase cannot access the genes
28
When does protein synthesis occur?
During interphase, as the genes in euchromatin can be freely transcribed. - this is a simple form of regulation as it ensures the proteins necessary for cell division are synthesised in time - prevents the energy-consuming and complex process of protein synthesis to occur during cell division
29
Why is DNA able to wound around histones?
DNA = -- charge Histones = + charge - in order to be packed into the nucleus of a cell - histones can be modified to increase/ decrease the degree of packing
30
How are histones modified?
The addition of acetyl groups OR phosphate groups reduce the + charge of histones. - once charge is reduced, DNA coils around histones less tightly - allowing certain genes to be transcribed HOWEVER... The addition of methyl groups makes histones more HYDROPHOBIC. - DNA coils around histones more tightly - prevents the transcription of genes
31
What is epigenetics?
A term used to describe the control of gene expression though the modification of DNA.
32
What is an operon?
A group of genes that are controlled by the same regulatory mechanism and expressed at the same time.
33
How are operons useful?
They are an efficient way of saving energy, as if a certain gene's products aren't needed - then all the genes involved in their production can be switched off.
34
What is the LAC OPERON?
A group of 3 genes - lacA, lacZ, lacY - involved in the metabolism of lactose - they are structural genes as they code for 3 enzymes and are transcribed onto a molecule of mRNA
35
What is the role of lacI?
A regulatory gene, located near to the operon. Codes for a repressor protein that prevents the transcription of the lac operon genes - in the ABSENCE of lactose.
36
What is down regulation?
Repressor protein - constantly produced - binds to operator - prevents RNA polymerase binding to DNA. = NO transcription taking place
37
What is the promoter?
The section of DNA that is the binding site for RNA polymerase.
38
Explain the role of cyclic AMP?
Rate of transcription needs to be increased. (to produce the required quantity of enzymes to metabolise lactose) - only possible when cAMP is bound to CRP
39
What is the product of transcription?
(precursor molecule) pre-mRNA ... mature mRNA
40
What is a 'cap'?
Modified nucleotide
41
Explain translational control?
(1) degradation of mRNA (2) binding of inhibitory proteins to mRNA - prevents binding to ribosomes - prevents protein synthesis (3) activation of initiation factors - bind mRNA to ribosomes
42
What does post-transcription control involve?
modifications to the proteins that have been synthesised - addition of non-phosphate groups - modifying amino acids and formation of bond (disulphide bridges) - folding/ shortening of proteins - modification by cAMP
43
What is 'morphogenesis'?
The regulation of the pattern of anatomical development.
44
What are homeobox genes?
A group of genes containing a homeobox.
45
What is a homeobox?
A section of DNA - 180 base pairs long - codes for part of a protein - 60 amino acids long
46
What does a homeobox code for?
Homeodomain (part of the protein) - binds to DNA and switches genes on/ off
47
Classify homeobox genes?
REGULATORY genes
48
What are hox genes?
1 group of homeobox genes - responsible for the correct positioning of body parts - found in gene clusters
49
How are body plans usually represented?
cross-section through the organism - shows fundamental arrangement of tissue structure
50
What are 'diploblastic' organisms?
Animals w/ 2 primary tissue layers
51
What are 'triploblastic' organism?
Animals w/ 3 primary tissue layers
52
What are somites?
Precursor populations of cells - develop individual vertebrae and associated structures
53
What are somites directed by?
Hox genes - to develop in a particular way - depending on their positioning the sequence
54
Types of symmetry - body shapes (3) ??
(1) Radial symmetry - top and bottom - no L or R (2) Bilateral - L and R - head and tail (3) Asymmetry - NO lines of symmetry
55
What can mitosis lead to?
- cell division - apoptosis (programmed cell death) apoptosis shapes diff body parts!! - removes unwanted cells and tissues cells undergoing apoptosis can also release chemical signals - stimulating mitosis and cell proliferation - remodelling of tissues
56
What is mitosis and apoptosis BOTH regulated by?
HOX GENES

A LEVEL Biology (4 decks)

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