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A-level Aqa Biology > (4) genetic information > Flashcards

(4) genetic information Flashcards

1
Q

what is the difference between DNA in eukaryotic cells and prokaryotic cells?

A

eukaryotic DNA: longer, linear
associated w histones (proteins) to form chromatin (substance that makes chromosomes)
(in membrane bound nucleus)

prokaryotic DNA: shorter, circular, not associated with histones, doesn’t have areas areas of non-coding DNA (loose in cytoplasm)

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2
Q

how are eukaryotic chromosomes structured in eukaryotic cells?

A

through supercoiling

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3
Q

what is the process of supercoiling?

A
  1. DNA = wrapped around histones, forming chromatin
  2. histones associate in groups of 8 to form nucleosomes (beads on a string)
  3. nucleosomes wrap around one another forming a solenoid fibre (tightly coiled structure)
  4. solenoid fibres wrap around scaffolding proteins
  5. solenoid itself is further coiled to save space -> supercoiling (makes up chromosomes as a whole)
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4
Q

what are the features of DNA that mitochondria and chloroplasts both contain?

A

circular DNA, no areas of non-coding DNA, not associated w proteins

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5
Q

what is the endosymbiont theory?

A

states that some of the organelles in eukaryotic cells were once prokaryotic microbes
(larger cell engulfed mitochondria/chloroplast by endocytosis and remained inside the host cell being able to replicate instead of being digested)

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6
Q

what is a gene?

A

a sequence of DNA which codes for a polypeptide / functional RNA
(present at a specific locus in the DNA molecule) s

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7
Q

what is the genetic code of an organism?

A

the sequence of bases along its DNA
contains thousands of genes/cistrons (each codes for a specific polypeptide)

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8
Q

what are the natures of the genetic code?

A
  1. universal
  2. degenerate
  3. non-overlapping
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9
Q

how is the genetic code universal?

A

the same sequences of bases codes for the same amino acids in all organisms

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10
Q

how is the genetic code degenerate?

A

each amino acid is coded for than more than one triplet

(triplet code because 20 amino acids
4 bases
4^3 produced 64 combination, adequate for 20 amino acids)

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11
Q

how is the genetic code non-overlapping?

A

each base is only part of one codon, and each codon codes for one amino acid

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12
Q

what is protein synthesis?

A

production of a chain of amino acids and forms a primary structure of a protein

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13
Q

what are the stages of protein synthesis? (brief)

A
  1. TRANSCRIPTION of gene in the NUCLEUS - mRNA is formed
  2. processing of mRNA
  3. TRANSLATION of mRNA in a RIBOSOME - a polypeptide chain is formed
  4. MODIFICATION of the protein
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14
Q

what is RNA and what is its structure?

A

RNA = polymer made up of repeating mononucleotide sub-units
forms a single strand where each nucleotide is made up of
- pentose sugar ribose
- one organic base ( AGUC)
- phosphate group

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15
Q

what are the characteristics of mRNA (messenger RNA)?

A

mRNA = a copy of a gene from DNA
created in the nucleus and then leaves the nucleus to carry the copy of the genetic code of one gene to a ribosome in the cytoplasm

mRNA =
short : (length of one gene so it can leave the nucleus)
short-lived : (temporarily help create protein and can carry out function before enzymes break it down)
single-stranded with codons (3 bases coding for a specific amino acid)

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16
Q

what is tRNA?
what is its function?

A

single polynucleotide chain that is clover-leaf shaped (held together by hydrogen bonds)

function: attach to one of the 20 amino acids and transfer this amino acid to the ribosome to create the polynucleotide chain

specific amino acids attach to specific tRNA molecules: determined by anticodon (3 bases complementary to codon on mRNA)

17
Q

what is the process of the transcription of DNA?

A
  1. DNA helicase breaks hydrogen bonds between the complementary base pairs, unzipping the 2 strands
  2. RNA polymerase binds base sequence binds to base sequence called the promoter region
    -> determines which way the RNA polymerase faces and which region is the template
  3. RNA polymerase moves along the DNA strand in a 5’ to 3’. As it passes over DNA bases, it forms a complementary mRNA strand from free RNA nucleotides
  4. As the pre-mRNA strand is produced the 2 strands of DNA starts to recoil recoil behind
  5. When a terminator region is reached, the DNA is no longer copied (pre-mRNA is ready for next stage of protein synthesis)
18
Q

how does the pre-mRNA form mRNA?

A

through SPLICING

a molecule called spliceosome removes the introns from the pre-mRNA strand, producing mRNA that only contains exons (sections that code for proteins)

leave the nucleus via a nuclear pore and the mRNA attaches to a ribosome

19
Q

what is the process of translation?

A
  1. mRNA strand attaches to a ribosome in the cytoplasm/RER, becomes attached to the start codon (AUG) at the 3’ end of the strand
  2. tRNA molecule with the complementary anticodon moves to ribosome and bonds with codon on mRNA (tRNA carries specific amino acid)
  3. the ribosome moves along the mRNA strand and another tRNA molecule attaches to the second codon, carrying the second amino acid
    2 amino acids are bonded by a peptide bond using an enzyme and ATP which is hydrolysed to provide the required energy
  4. another tRNA moves into a ribosome, adding another amino acid to the chain, the first tRNA molecule is released from its amino acid and is free to collect another amino acid from the amino acid pool in the cell
  5. process continues until the ribosome reaches a stop codon on the mRNA strand
    no tRNA for stop codon so the process stops and the polypeptide chain is complete
20
Q

what is meant by the term ‘mutation’?
what are the 2 types?

A

a change in the amount of structure of DNA
point mutation
chromosome mutation

21
Q

what is point mutation?

A

a change in the sequence of a gene, which can cause a change in the polypeptide chain
caused by errors that occur during DNA replication

22
Q

what is chromosome mutation?

A

a change in the number/structure of the chromosomes
caused by errors that occur during cell division

23
Q

what are the different types of point mutation?

A

nonsense
silent
missense
frameshift

24
Q

what is nonsense point mutation and what is its effects on the polypeptide chain?

A

results in a stop codon being coded for
prevents the rest of the polypeptide chain from being produced

25
Q

what is silent point mutation and what is its effects on the polypeptide chain?

A

results in the same amino acid being coded for (As genetic code is degenerate)
no change in polypeptide produced

26
Q

what is missense point mutation and what is its effects on the polypeptide chain?

A

results in different amino acid being coded for
could affect structure and function of the polypeptide

27
Q

what is frameshift point mutation and what is its effects on the polypeptide chain?

A

alters the reading frame of the gene downstream of the mutation
causes all triplets downstream to be different, affecting all amino acids coded for

28
Q

what are the 4 types of chromosomal mutation?

A

translocation
duplication
inversion
deletion

29
Q

what is translocation?

A

an exchange of genetic material between non-homologous chromosomes

30
Q

what is duplication?

A

when an extra copy of a part of a chromosome is inserted adjacent to the original copy
often a benign mutation
2nd copy of gene is usually not expressed (mutation = harmless)

31
Q

what is inversion?

A

when a chromosome breaks and rearranges itself to form a partial inversion of its genetic sequence
no genetic information is lost so mutation is benign

32
Q

what is deletion?

A

the loss of one or more genes from a chromosome
polypeptide is unlikely to function correctly, one deleted nucleotide causes all triplets to be read differently in a sequence

33
Q

what is meiosis?

A

involves 2 nuclear divisions
produces 4 genetically different haploid gametes from a single diploid parent cell

34
Q

what are the two mechanisms in meiosis which introduce variation?

A

independent segregation of homologous chromosomes
crossing over of homologous chromosomes
both occur during meiosis 1

35
Q

what is independent segregation?

A

in meiosis 1, homologous pairs of chromosomes line up opposite each other at the equator of the cell
it is random which side of the equator of the paternal and maternal chromosomes from each homologous pair lie
these pairs are separated so one of each homologous pair ends up in the daughter cell

36
Q

what is crossing over?

A

during meiosis: non sister chromatids can exchange pairs of themselves with their homologous chromosome to make recombinant chromosomes

  1. non-sister chromatids overlap and twist around eachother forming a bivalent
  2. produces tension and twisted portions breaks off at the chiasm a
  3. broken regions join to homologous partner
37
Q

what happens in meiosis 1?

A

before meiosis: interphase happens, doubling the DNA
prophase 1: chromatin condenses and nucear membrane dissipates
metaphase 1: spindles sort the chromosomes into homologous pairs but align them randomly in pairs on the equator (independent assortment)
-> crossing over also happens
anaphase 1 + telophase 1: chromosomes pulled by spindles to opposite poles

making 2 haploid cells

38
Q

what happens in meiosis 2?

A

same as mitosis

39
Q
A

A-level Aqa Biology (7 decks)

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