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AS AQA BIOLOGY > Genes and variation > Flashcards

Genes and variation Flashcards

(53 cards)

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1
Q

Define gene

A

A section of DNA in a chromosome coding for one if more polypeptides

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2
Q

Define locus

A

The position of a gene on a chromosome

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3
Q

What does the gene code for

A

Amino acid sequence of a polypeptide

A functional RNA including ribosomal RNA and transfer RNA

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4
Q

How many DNA bases code for an amino acid? Why?

A

3

  • Only 20 amino acids regularly occur in proteins
  • Each amino acid must have its own code of bases on the DNA
  • If each base coded for a different amino acid only 4 amino acid could be coded
  • pairs would make 16
  • threes make 64 which satisfies 20
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5
Q

Outline 5 features of the genetic code?

A
  • Two amino acids are coded for by a single codon
  • The remaining are coded by 2-6
  • degenerate code
  • triplet is always read in one direction
  • the start of the sequence is always coded by one codon
  • three codons are stop codons
  • each base is only read once (non-overlapping)
  • universal coding in all organisms
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6
Q

Define exon

A

Coding sequence of bases

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7
Q

Define intron

A

Non-coding sequences of bases

Code for something else

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8
Q

Outline how DNA is in a prokaryote

A

Shorter
Circular
Not associated with proteins (histones)
No chromosomes

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9
Q

Outline how DNA is in a eukaryote

A 
Longer
Linear
Linked to proteins (histones) 
Form chromosomes 
Mitochondria and chloroplasts contain prokaryote like DNA
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10
Q

Outline the structure of a chromosome

A

Dispersed throughout the nucleus until cell division

DNA double helix appears as two threads joined by a single point (chromatids)

DNA molecule
DNA with histones
Coiled DNA histones complex
Coils fold to form loops
Loops coil and pack together to form a chromosome
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11
Q

Define allele

A

Alternative form of a gene

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12
Q

Define cancer

A

A disease resulting from mutations that lead to uncontrolled cell division

Forms a group of abnormal cells called a tumour

From which cells may break away and form secondary tumours elsewhere

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13
Q

Define chromosome

A

A thread like structure made up from one long DNA molecule

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14
Q

Define chromatid

A

One arm of a double stranded chromosome

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15
Q

Define centriole

A

Tiny bundles of protein that form a network of protein fibres called the spindle

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16
Q

Define centromere

A

The point at which 2 strands of a chromosome are joined together

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17
Q

Define crossing over

A

When chromatids twist around each other
and bits of them swap over during meiosis
alleles are exchanged between homologous chromosomes

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18
Q

Define differentiation

A

The process by which cells become specialised

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19
Q

Define diploid

A

When a cell contains 2 copies of each chromosome (body cell)

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20
Q

Define haploid

A

When a cell contains 1 copy of each chromosome (gametes)

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21
Q

Define genotype

A

The alleles an organism has

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22
Q

Define histone

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A

Protein that DNA is wound around in order to fit into the nucleus

23
Q

Define homologous pair

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A

A pair of matching chromosomes - same genes but different alleles

24
Q

Define independent segregation

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A

During meiosis 1 when homologous pairs of chromosomes are arranged randomly in a line

Resulting in a random combination of maternal and paternal chromosomes in daughter cells

25
Define sister chromatids
2 identical copies of a chromosome joined together in the middle
26
What are the two types of RNA important in protein synthesis
``` Messenger RNA (mRNA) Transfer RNA (tRNA) ```
27
Define genome
The complete set of genes in a cell including those in the mitochondria and or chloroplasts
28
Define proteome
The full range of proteins produced by the genome This is sometimes called the complete proteome In which chase the term proteome refers to the proteins produced under a certain set of conditions
29
What does mRNA do
Associated with ribosomes To act act as a template for protein synthesis
30
What does tRNA do
Binds to a specific amino acid Hosts the anticodon Takes the amino acid to the ribosome for protein synthesis
31
Compare DNA, mRNA and tRNA. Outline 4
DNA double, RNA single DNA larger, mRNA smaller, tRNA smallest DNA double helix, mRNA single helix, tRNA clover shaped DNA Deoxyribose, RNA Ribose DNA Thymine, RNA Uracil DNA Mostly in nucleus, RNA throughout the cell DNA is constant quantity, RNA varies DNA chemically stable, mRNA least, tRNA in middle
32
Define transcription
The process by which DNA is used to form pre mRNA
33
Define splicing
The process by which introns are removed from pre mRNA forming mRNA
34
Define translation
The process by which mRNA is used to form a polypeptide
35
Outline transcription
1) RNA polymerase binds to the DNA and separates the two strands 2) RNA polymerase binds matching nucleotides to the template strand forming pre-mRNA 3) DNA is rejoined together as the pre-mRNA is made 4) Once the stop codon is recognised RNA polymerase detaches
36
Outline splicing
1) the pre-mRNA's introns are looped together 2) the introns are spliced out of the pre-mRNA 3) until only the exons remain 4) mRNA then leaves the nucleus via the nuclear pore
37
Outline translation
1) tRNA binds to its complementary amino acid 2) tRNA and mRNA are brought to the rRNA (ribosome) 3) Anti-codons on the tRNA are complementary to the codons on the mRNA 4) The ribosome forms a peptide bond between the amino acids 5) this is done two at a time until a polypeptide is formed
38
Define mutation
A change to the quantity of base sequence of the DNA of any organism
39
What are the 3 different types of point mutation?
Silent Nonsense Missense (conservative/non-conservative)
40
Define silent mutation
Change in the codon that still codes for the same amino acid, resulting in no change to the phenotype
41
Define nonsense mutation
A change in the codon that results in a premature stop codon, shortening the polypeptide chain length
42
Define missense mutation
A change in the codon resulting in the production of a different amino acid
43
What are the 5 types of mutation? (chromosomal and gene)
``` Addition Deletion Translocation Inversion Duplication ```
44
What are the two types of gene mutation?
Point mutation | Reading Frame Shift
45
Explain point mutation
A substitution of one base for another base resulting in a different codon
46
Explain reading frame shift mutation
A deletion or addition of a base to a codon, resulting in the reading frame shifting resulting in a completely different polypeptide chain
47
Outline the difference between spontaneous and induced mutations
Spontaneous mutations arise during meiosis and do not affect the parents whereas induced mutations arise from mutagens and exposure to hazards in our environment
48
Name three changes in the environment can induce mutation
``` Radiation Diet Viruses Smoking Alcohol Chemical exposure ```
49
Define proto-oncogene
Codes for a protein that stimulates normal cell growth and divsion
50
Define tumour suppressor gene
Code for proteins that inhibit uncontrolled cell division
51
Define oncogenes
Mutated proto-oncogenes that increase proteins that stimulate growth and division and increase activity of each growth stimulating molecule
52
Define mutated tumour suppressor gene
Mutated tumour suppressor gene that cannot repair damaged DNA, control cell adhesion or inhibit cell division
53
What are the two types of mutation in chromosomes
Polyploidy (multiple sets of chromosomes) | Non-disjunction (different number of individual chromosomes)

AS AQA BIOLOGY (8 decks)

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