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AS biology > genetic information and variation > Flashcards

genetic information and variation Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

what are the differences between eukaryotic dna and prokaryotic dna?

A
  • eukaryotic dna is longer, prokaryotic dna is shorter (use of histones)
  • eukaryotic dna is linear, prokaryotic dna is circular
  • eukaryotic dna contains introns, prokaryotic dna does not
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2
Q

what is a chromosome?

A

-long linear dna that is associated with histone proteins
- found in the nucleus of eukaryotic cells

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3
Q

what is a gene?

A

a sequence of DNA (nucleotide) bases that code for:
- the amino acid sequence of a polypeptide
- or a functional RNA (tRNA or rRNA)

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4
Q

what is a locus?

A

fixed position a gene occupied on a particular DNA molecule

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5
Q

what is a triplet code?

A

a sequence of 3 DNA bases, called a triplet, codes for a specific amino acid

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6
Q

what does it mean when a genetic code is universal?

A

the same base triplets codes for the same amino acid in all organisms

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7
Q

what is a non overlapping genetic code?

A

each base is oath of only one triplet so each triplet is read as a discrete unit

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8
Q

what is a degenerate genetic code?

A

an amino acid can be coded for by more than one base triplet

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9
Q

what are non coding base sequences and where are they found?

A

DNA that does not code for amino acid sequences/ polypeptides:
1. between genes- e.g non coding multiple repeats
2. within genes- introns

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10
Q

what are exons?

A

base sequence of a gene coding for amino acid sequences (in a polypeptide)

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11
Q

what are introns?

A

base sequence of a gene that doesn’t code for amino acids, in eukaryote cells

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12
Q

what is a genome?

A

the complete set of all genes in a cell

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13
Q

what is a proteome?

A

the full range of proteins that a cell can produce (coded for by the cells DNA)

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14
Q

what are the two stages of protein synthesis?

A
  1. transcription
  2. translation
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15
Q

what is transcription?

A

production of messenger RNA from DNA in the nucleus

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16
Q

what is translation?

A

the production of polypeptides from the sequence of codons carried by mRNA, at ribosomes

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17
Q

what is the similarity between the structure of tRNA and mRNA?

A

both single polynucleotide strands

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18
Q

what are the differences between the structure of tRNA and mRNA?

A

-tRNA is folded into a clover leaf shape, whereas mRNA is linear
-tRNA has hydrogen bonds between paired bases, mRNA doesn’t
-tRNA has an anticodon, mRNA has codons
-tRNA is a shorter fixed length, whereas mRNA is a longer, variable length (more nucleotides)
-tRNA has an amino acid binding site, mRNA doesn’t

19
Q

describe how mRNA is formed by transcription in eukaryotic cells

A
  1. occurs in the nucleus of the cell
  2. hydrogen bonds between DNA bases break (catalysed by helicase)
    3.only one DNA strand acts as a template
  3. free RNA nucleotides align next to their complementary bases on the template strand
    -in RNA, uracil is used in place of thymine
  4. RNA polymerase joins adjacent RNA nucleotides
  5. this forms phosphodiester bonds via condensation reactions
  6. pre-mRNA is formed and this is spliced to remove introns forming mRNA
20
Q

describe how production of mRNA in a eukaryotic cell is different from the production of mRNA in a prokaryotic cell?

A
  • pre-mRNA produced in eukaryotic cells, whereas mRNA is produced differently in prokaryotic cells
  • because genes in prokaryotic cells don’t contain introns so no splicing can occur in prokaryotic cells
21
Q

describe how translation leads to the production of a polypeptide

A
  1. mRNA attaches to a ribosome and the ribosome moves to a start codon (AUG)
  2. tRNA brings a specific amino acid
  3. tRNA anticodon binds to the complementary mRNA codon
  4. ribosomes moves along to next codon and another tRNA binds so 2 amino acids can be joined by a condensation reaction forming a peptide
    -using energy from the hydrolysis of atp
  5. tRNA released after amino acid joined polypeptide
  6. ribosome moves along mRNA to form the polypeptide, until a stop codon is reached
22
Q

describe the role of ATP in translation?

A
  • hydrolysis of ADP + Pi releases energy
  • so amino acids join to tRNAs and peptide bonds form between amino acids
23
Q

describe the role of tRNA in translation

A
  • attaches to/ transports a specific amino acid, in relation to its anticodon
  • tRNA anticodon complementary base pairs to mRNA codon, forming hydrogen bonds
  • 2 tRNAs brings amino acids together so peptide bonds can form
24
Q

describe the role of ribosomes in translation

A
  • mRNA binds to ribosome, with space for 2 codons
  • allows tRNA with anticodons to bind
  • catalyses formation of peptide bond between amino acids
  • moves along (mRNA to the next codon)/ translation
25
Q

what is a gene mutation?

A
  • a change in the base sequence of DNA (on chromosomes)
  • can arise spontaneously during DNA replication (interphase)
26
Q

what is a mutagenic agent?

A

a factor that increases rate of gene mutation
e.g UV light or alpha particles

27
Q

explain how a mutation can lead to the production of a non functional protein or enzyme

A
  1. changes sequence of base triplets in DNA so changes codons on mRNA
  2. so changes sequence of amino acids in the polypeptide
  3. so changes position of hydrogen, ionic and disulphide bonds
  4. so changes protein tertiary structure of protein
  5. enzymes- active site changes shape so substrate can’t bind. enzyme substrate complex can’t form
28
Q

explain the possible effects of a substitution mutation

A
  1. base in DNA replaced by a different base
  2. this changes one triplet so changes one mRNA codon
  3. so one amino acid in polypeptide changes
    -tertiary structure may change if position of hydrogen/ionic/disulphide bonds change
    - or amino acid doesn’t change due to degenerate nature of genetic code or if mutation is in an intron
29
Q

explain the possible effects of a deletion mutation

A
  1. one base removed from DNA sequence
  2. changes sequence of DNA triplets from point of mutation
  3. changes sequence of mRNA codons after a point of mutation
  4. changes tertiary structure
30
Q

describe the difference between haploid and diploid cells

A

diploid- has 2 complete sets of chromosomes, represented at 2n
haploid- has a single set of unpaired chromosomes, represented as n

31
Q

what occurs in the first stage of meiosis?

A
  • separates homologous chromosomes
  • chromosomes arrange into homologous pairs
  • independent segregation of homologous chromosomes
32
Q

what occurs in the second stage of meiosis?

A

this is where the chromatids separate out to produce 4 haploid gametes

33
Q

explain how crossing over creates genetic variation

A

-homologous pairs of chromosomes associate/ form a bivalent
-chiasmata form
-alleles/ chromatids exchanged between chromosomes
- creating new combinations of alleles on chromosomes

34
Q

explain how independent segregation creates genetic variation

A

-homologous pairs randomly align at the equator
-so creating different combinations of alleles in daughter cells

35
Q

other than mutation and meiosis, explain how genetic variation within a species is increased

A

-random fertilisation
-creating new allele combinations

36
Q

explain the different outcomes of mitosis and meiosis

A
  1. mitosis produces 2 daughter cells, meiosis produces 4 daughter cells
  2. mitosis maintains the chromosome number, whereas meiosis halves the chromosome number- as homologous chromosomes separate in meiosis but not mitosis
  3. mitosis produces genetically identical daughter cells, whereas meiosis produces genetically varied daughter cells
37
Q

explain the importance of meiosis

A

-two divisions create haploid gametes (halves number of chromosomes)
-so diploid number is restored at fertilisation, chromosome number maintained between generations
-independent segregation and crossing over creates genetic variation

38
Q

describe how mutations in the number of chromosomes arise

A

-spontaneously by chromosome non-disjunction during meiosis
-homologous chromosomes (meiosis I) or sister chromatids (meiosis II) fail to separate during meiosis
-so some gametes have an extra copy (n+1) of a particular chromosome and others have none (n-1)

39
Q

what is genetic diversity

A

number of different alleles in a population

40
Q

what are alleles and how do they arise

A

variations of a particular gene (same locus) -> different DNA base sequence
-they arise by mutations

41
Q

what is a population

A

a group of interbreeding individuals all of the same species

42
Q

genetic diversity

A

number of different alleles of genes in a population

43
Q

importance of genetic diversity

A

enables natural selection to occur

44
Q
A

AS biology (7 decks)

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