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

Chapter 19 Genetics Of Living Systems Flashcards

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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
Q

How is DNA packed into the nucleus of a cell?

A

DNA is a very long molecule and must be wound around proteins (histones).
- results in a DNA/ protein complex

= CHROMATIN

26
Q

What are the 2 types of chromatin?

A

(1) Heterochromatin
- tightly wound
- chromosomes visible during cell division

(2) Euchromatin
- loosely wound
- present during interphase

27
Q

When is transcription of genes NOT possible?

A

When DNA is tightly wound - heterochromatin.

  • RNA polymerase cannot access the genes
28
Q

When does protein synthesis occur?

A

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
Q

Why is DNA able to wound around histones?

A

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
Q

How are histones modified?

A

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
Q

What is epigenetics?

A

A term used to describe the control of gene expression though the modification of DNA.

32
Q

What is an operon?

A

A group of genes that are controlled by the same regulatory mechanism and expressed at the same time.

33
Q

How are operons useful?

A

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
Q

What is the LAC OPERON?

A

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
Q

What is the role of lacI?

A

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
Q

What is down regulation?

A

Repressor protein - constantly produced - binds to operator - prevents RNA polymerase binding to DNA.

= NO transcription taking place

37
Q

What is the promoter?

A

The section of DNA that is the binding site for RNA polymerase.

38
Q

Explain the role of cyclic AMP?

A

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
Q

What is the product of transcription?

A

(precursor molecule) pre-mRNA … mature mRNA

40
Q

What is a ‘cap’?

A

Modified nucleotide

41
Q

Explain translational control?

A

(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
Q

What does post-transcription control involve?

A

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
Q

What is ‘morphogenesis’?

A

The regulation of the pattern of anatomical development.

44
Q

What are homeobox genes?

A

A group of genes containing a homeobox.

45
Q

What is a homeobox?

A

A section of DNA

  • 180 base pairs long
  • codes for part of a protein - 60 amino acids long
46
Q

What does a homeobox code for?

A

Homeodomain (part of the protein)

  • binds to DNA and switches genes on/ off
47
Q

Classify homeobox genes?

A

REGULATORY genes

48
Q

What are hox genes?

A

1 group of homeobox genes

  • responsible for the correct positioning of body parts
  • found in gene clusters
49
Q

How are body plans usually represented?

A

cross-section through the organism

  • shows fundamental arrangement of tissue structure
50
Q

What are ‘diploblastic’ organisms?

A

Animals w/ 2 primary tissue layers

51
Q

What are ‘triploblastic’ organism?

A

Animals w/ 3 primary tissue layers

52
Q

What are somites?

A

Precursor populations of cells

  • develop individual vertebrae and associated structures
53
Q

What are somites directed by?

A

Hox genes - to develop in a particular way - depending on their positioning the sequence

54
Q

Types of symmetry - body shapes (3) ??

A

(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
Q

What can mitosis lead to?

A
  • 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
Q

What is mitosis and apoptosis BOTH regulated by?

A

HOX GENES

A LEVEL Biology (4 decks)

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