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a level biology aqa > UNIT 4, Topic 4A & 4B - DNA, Protein Synthesis, Diversity, and Classification > Flashcards

UNIT 4, Topic 4A & 4B - DNA, Protein Synthesis, Diversity, and Classification Flashcards

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1
Q

a gene occupies…

A

a fixed position called a locus on a particular DNA molecule

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2
Q

gene

A

A gene is a base sequence of DNA that codes for : amino acid sequence of a polypeptide, and, a functional RNA (including ribosomal RNA and tRNA)

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3
Q

functional RNA

A

Functional RNAs areRNA molecules that are not translated into proteins

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4
Q

ribosomal RNA

A

Ribosomal RNA arethe subunits on a ribosome.

Ribosomes are the organelles where proteins are formed in a cell. It consists of a large and small subunit that is made up of ribosomal RNA (rRNA).

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5
Q

DNA

A

A chemical polymer (polynucleotide) that stores genetic information for a cell

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6
Q

loci

A

a fixed position a gene occupies on a chromosome

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7
Q

allele

A

alternative form of a gene (in the same loci and chromosome) that’s caused by random mutations mostly

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8
Q

codon

A

3 mRNA molecules
“3 bases code for one amino acid”

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9
Q

primary structure of protein…

A

the UNIQUE sequence of amino acids

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10
Q

genome

A

the complete set of genes / genetic make up in a cell

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11
Q

proteome

A

the entire set of proteins expressed by a genome: all the proteins a cell is able to code for

  • use this phrasing as not all proteins can or are made at the same given time
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12
Q

give 3 features of eukaryotic DNA

A
  • linear (and enclosed in a nucleus)
  • long
  • bundled into chromosomes
  • contains histones (proteins)
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13
Q

Give 3 features of prokaryotic DNA

A
  • short
  • circular DNA (plasmids)
  • does not contain/ associated with proteins (histones)
  • found in the cytoplasm (no nucleus)
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14
Q

histones

A

The protein that DNA molecule wraps around, also provides structural support for a chromosome

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15
Q

introns

A

sections of a gene that are not expressed in final RNA products (aka dont code for amino acids)

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16
Q

exons

A

coding regions of a gene that code for a protein / amino acid sequence (they are the reason for splicing)

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17
Q

what is the genetic code?
what’s a triplet code?

A

Described as a sequence of bases (adenine, guanine, cytosine, thymine) which, when arranged in a certain order, code for specific amino acids.
A triplet code describes how an amino acid is coded for by a group of 3 bases.

(note that codons actually code for an amino acid during transcription, hence the codon table. The tRNA, anticodon, is just essentially used as a carrier for the amino acid because it’s complementary to the mRNA’s codon)

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18
Q

What determines the sequence of amino acids?

A

the order of bases to form a polypeptide (each with a different amino acid sequence).

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19
Q

after the primary structure, how does the tertiary structure help define the protein / polypeptide chain?

A

Hydrogen, ionic, and disulfide bonds form between the R groups on the amino acid causing the chain to fold further and form a protein, and this gives it its function, such as an enzyme

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20
Q

why do different species have different base sequences?

A

(mutations)
In terms of proteins, they need different Gene’s to be able to make different proteins

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21
Q

read…

A

correct order:
1. DNA base sequence codes for…
2. (after transcription and translation) amino acid sequence determines…
3. polypeptide chain determines…
4. (after folding) protein structure and function

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22
Q

practice some Exam Qs

A

.

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23
Q

bonds in polypeptide chain

A

peptide

24
Q

3 code words used to describe DNA

A

degenerate, universal, non-overlapping

25
Q

degenerate code
why is this advantageous?

A

Several base triplets can code for the same amino acid.
- e.g. only 20 amino acids but 64 possible combinations of triplets

Its advantageous as despite mutations, theres a chance that the mutation won’t have an affect in the amino acid coded for in the end

26
Q

non-overlapping code

A

Each base in sequence is read only once!
So the base cytosine in ATC, for example, would not be read twice for the next triplet

27
Q

read

A

DNA: triplet
mRNA: codon
tRNA: anticodon

28
Q

universal code
- what does this suggest about evolution?

A

the same specific base triplets code for the same amino acids - in all living things.
- Suggesting we all have a common ancestor.

29
Q

heterozygous

A

(might not be on spec)
non identical alleles

30
Q

Extra features of eukaryotic DNA

A
  1. wrapped around histones
  2. mitochondria and chloroplasts have their own DNA
  3. most DNA doesn’t code for polypeptides
31
Q

What are the 2 purposes of histones

A
  1. Allows large DNA molecule to be stored compact by wounding the linear DNA around it. Then, associated proteins and DNA are coupled up tightly to form a chromosome
  2. They help support the DNA
32
Q

Describe the DNA found in mitochondria and chloroplasts (organelles only have their own DNA in eukaryotic cells)

A

It’s similar to prokaryotic: short, circular, and not associated with proteins. (can link to suggests commona ancestor)

33
Q

Explain why most DNA in eukaryotes doesn’t code for polypeptides

A

some genes code for functional RNA instead of polypeptides (which is also ribosomal and tRNA).
Additionally, the genes that do code for polypeptides contain non-coding regions as well as coding (introns and exons).

34
Q

Multiple repeats?

A

These are regions in eukaryotic DNA base sequences that occur outside of Gene’s. They repeat many times but do not code for amino acids.

  • non-coding repeats
    e.g. CGCGCGCGCGCG and you would describe this repeating sequence of GC to be 12 bases long.
35
Q

in the definition of a gene you dont have to include…

A

the fact exons and introns exist

36
Q

2 types of non coding DNA

A

non- coding/ multiple repeats and introns

37
Q

genome

A

the complete set of genes in a cell.

38
Q

proteome

A

full range of proteins that the cell can code for / produce

39
Q

what’s the link between the genome and proteome?

A

Proteome is as a result of the full genome; as it contains genes that code for specific proteins.

40
Q

protein synthesis definition, and define translation and transcription

A

The production of polypeptides (that fold to form proteins) within the cell using the genetic code, 2 parts: transcription and translation.

Transcription: the production of mRNA from DNA (different in prokaryotes and eukaryotes)
Translation: the production of polypeptides from the sequences of codons carried by mRNA.
- DNA and RNA are involved in these stages

41
Q

what are the 3 different terms used to describe a group of 3 bases

A

triplet, codon and anticodon

42
Q

What are the 4 causes of genetic variation?

A
  1. a change in DNA base sequence (gene mutation)
  2. meiosis: independent segregation of homologous chromosomes and crossing over
  3. chromosomal mutations (non-disjunction)
  4. random fertilisation of gametes
43
Q

where do gene mutations come from?

A

arise spontaneously in DNA replication (base deletion, substitution…)
AND due to degenerate nature of the genetic code, not all substitutions cause a change in the encoded sequence of amnio acids

44
Q

what can increase the rate of gene mutations?

A

mutagenic agents

45
Q

types of gene mutations

A

duplication, addition, translocation, substitutions, deletion

46
Q

example of mutagenic agents

A

carcinogenics (such as from sun damage/ overexposure to UV)

47
Q

Why do you think gene mutations arise during interphase?

A

Stage includes replication:
this is when the bases are exposed and not protected by the DNA double helix structure or any bonds and so are vulnerable

48
Q

which type of 3 bases is affected by mutations, such as substitution?

A

Triplets

49
Q

Exam Q feedback:

A

Q: a mutation can lead to the production of a non-functional enzyme, explain.

Missed a mark for not stating the names of the bonds in the tertiary srructure

50
Q

Suggest what deletion mutations have a worse impact than substitution mutations.

A

(using info from Q)
Substitution makes TGC be coded for TAC instead, only affecting one triplet.

Deletion makes a frameshift; shifts entire sequence changing almost every each amino acid coded for as triplets have shifted (using info again) and this is worse due to the non-overlapping nature where triplets are read in 3s and the same base of a triplet is not read twice.

51
Q

2 amino acids sequences had experienced substitution mutations, only one was affected.
Explain why (for both)

A

1st substitution was harmless and had no impact on the amino acid sequence due to the degenerate code.

2nd changed an amino acid in the sequence which could alter the protein structure and potentially making it non-functional …
(only if that change happens to be in the active site of a tertiary structure of an ENZYME or is an amino acid that’s involved in forming bonds such as ionic, hydrogen or sulfide bridges for example)

  • 2 questions in one
52
Q

Where does meiosis occur?

A

in reproductive organs (mostly)

53
Q

purpose of meiosis

A

to produce haploid cells called gametes

54
Q

reason for having haploid daughter cells, importance, and what would happen if meiosis didn’t occur?

A

to maintain chromosome number of species the same, necessary
- gametes would have the normal number of chromosomes in a haploid cell, causing the zygote after fertilisation to contain the incorrect amount of chromosmes

55
Q

daughter calls number in meiosis

A

4

56
Q

purpose of meiosis?

A

producing sex gametes with genetic variation that MAY later be used in sexual reproduction to create a zygote (new life)

when you see 2n on a diagram go to just n.

57
Q

purpose of mitosis?

A

cloning body cells for growth and repair

a level biology aqa (6 decks)

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