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Biology Y12 > DNA, Genes, Protein Synthesis > Flashcards

DNA, Genes, Protein Synthesis Flashcards

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1
Q

where is genetic information stored?

A

Genetic information is stored by genes which are arranged on chromosomes

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2
Q

how many pairs of homologous chromosomes are there?

A

26

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3
Q

what are homologous chromosomes?

A

Pairs of matching chromosomes which are same in size and contain the same genes but may contain different alleles.

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4
Q

what is an allele?

A

A different form of a particular gene, positioned in the same relative position (locus) on homologous chromosomes

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5
Q

what is a gene?

A

a agene is a base sequence of DNA that codes for:
- the amino acid sequence of a polypeptide
- the functional RNA (including rRNA & tRNA)

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6
Q

each gene has a unique sequence of bases which determine the..?

A

amino acid sequence in the polypeptide (protein)

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7
Q

what gives us a unique trait/phenotype?

A

It is these proteins and combination of proteins that give us a unique phenotype (trait).

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8
Q

Differences in base sequences of alleles of a single gene may result in…?

A

non-functional proteins (e.g enzymes)

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9
Q

explain DNA storage within Eukaryotes?

A

These contain linear DNA that exist as chromosomes. The DNA molecule is really long, so it has to be wound up around proteins called histones so that it can fit into the nucleus.

Histone proteins also help to support the DNA. The DNA is then coiled up very tightly to make a compact chromosome.

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10
Q

explain DNA storage within a prokaryote?

A

The DNA molecules are, shorter and circular.

Prokaryotes still carry DNA as chromosomes- most just have 1 chromosome

The DNA isn’t wound around histones…it condenses to fit in the cell by supercoiling.

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11
Q

this can show evidence for what?

A

evolution

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12
Q

what’s the difference between DNA features of prokaryotic and eukaryotic cells
(5 differences)

A
  • the relative length of DNA in prokaryotes is very short whereas in DNA is very long as it contains many genes
  • in prokaryotes DNA is circular (forming a closed loop) and in eukaryotes DNA is linear forming part of a chromosome
  • in prokaryotes there is only one different molecules per cell whereas in eukaryotes there are more than 1 different molecules per cell.
  • in prokaryotes there are no proteins’ association with proteins whereas in eukaryotes there are histones which DNA is wounds up around so it can fit in the nucleus
  • in prokaryotes non-coding DNA is absent/not there but in Eukaryotic cells non-coding DNA is present within genes (introns) and as non-coding multiple repeats between genes
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13
Q

mitochondrial and chloroplast have their own DNA , what is it similar to?

A
  • similar to prokaryotic DNA
  • circular and shorter, not associated with histones
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14
Q

the genetic code

A
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15
Q

what is the genetic code?

A

The genetic code is the sequence of bases along its DNA.

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16
Q

what are the features of the genetic code?

A

Universal

Non-overlapping

Degenerate

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17
Q

what is meant by the genetic code is universal?

A

The genetic code is almost universal – the same sequence of bases codes for the same amino acids in all organisms.

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18
Q

explain how this is an advantage?

A

helps in gene technologies such as genetic engineering

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19
Q

DNA has the …?
mRNA has …?
tRNA has ..

A

triplet code
codons
anti-codons

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20
Q

how is mRNA built up?

A

by complimentary base pairing using the DNA as a template

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21
Q

the DNA base triplets are converted into..?

A

mRNA codons.

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22
Q

what is meant by the genetic code is non-overlapping?

A

The genetic code is non-overlapping: each base is only part of one triplet/codon, and each triplet/codon codes just one amino acid.

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23
Q

explain why this is an advantage?

A

if a point mutation occurs it will only affect one codon and therefore one amino acid

24
Q

what is meant by the code is degenerate?

A

The triplet code is degenerate, which means that each amino acid is coded for by more than one triplet.

25
Q

how many amino acids are there?

A

20

26
Q

how many amino acids does the genetic code have to code for?

A

all 20 amino acids

27
Q

since there are 4 DNA bases, therefore 3 bases are needed to…?

A

make enough combinations to code for at least 20 amino acids

28
Q

this can be proven mathematically using 4n. what do they stand for?

A

4 - number of bases
n - number of bases that make up our code

29
Q

if one base coded for 1 amino acid this would only allow ..? amino acids to be coded. this is insufficient to code for 20 AA

if two bases coded for 1 amino acid this would allow ..? amino acids to be coded. this is insufficient to code for 20 AA

if three bases coded for 1 amino acid this would allow ..? amino acids which is …?

A

4 , 16 , 64 which is sufficient to code for 20 amino acids

30
Q

how is the code being degenerate an advantage?

A
  • helps during point mutation, so if one of the bases change in the triplet it could still code for the same amino acid
31
Q

what else does this tell us?

A

64 combinations is more than enough to code for 20 amino acids, as a result each amino acids is actually coded for by more than 1 triplet of bases. this is what is meant by the code is degenerate

32
Q

what is the start codon? what is its’s role?

A

at the start of a gene, there is a first triplet in DNA - TAC and RNA - AUG this initiates translation

33
Q

what is the stop codon?

A

the final three bases(triplet) that do not code for an amino acid. these stop codons and mark the end of the polypeptide chain. and cause ribosomes to de-attach and therefore causes translation to stop. these codons are ATT, ATC AND ACT on DNA

34
Q

experimental evidence for the genetic code

A
35
Q

describe the experiment by American scientist Nirenberg that led to the discovery of the genetic code?

A

they created a cell-free extract by rupturing the cell walls of E.coli bacteria to release their contents. DNA was destroyed using enzymes. the scientists produced RNA composed solely of UUUUUU (uracil nucleotides). they then added this synthetic poly-U RNA into the cell-free extract. they set up 20 test tubes with 20 different amino acids, but they were radioactively labelled. they incubated the tubes and polypeptide synthesis occurred in each tube. they then extracted the polypeptides from the solution.

36
Q

one tube was found to be radioactive. which amino acid was radioactive?

A

amino acid = phenylalanine, Nirenberg and Matthaei had therefore found that the UUU codon could be translated into the amino acid phenylalanine.

37
Q

explain how Niremberg conducted further experiments

A
  • found how many bases would be in a codon
  • added various synthetic RNA’s to the cell-free extract. for the following synthetic RNA’s.
38
Q

which amino acids were incorporated in the resulting polypeptides?

A
  • poly-A RNA incorporated = lysine
  • poly-C RNA incorporated = proline
  • poly U, C RNA incorporated = leucine and serine
39
Q

what did he do to discover a codons length?

A

Niremberg created a synthetic cellulose filter that ribosomes could attach to. tRNA, poly-U RNA and phenylalanine would wash through. he poured 2 different mixtures over separate filters
1. ribosomes, tRNA and radioactive phenylalanine
2. ribosomes, tRNA poly-U RNA and radioactive phenylalanine

40
Q

he poured through a washing solution and analysed the filters for radioactivity. only the filter from experiment 2 was radioactive. explain why.

A

the ribosomes attach to the poly-U RNA and tRNA and start to synthesise radioactive uracil. these complexes bind to foldes

41
Q

what was one of the final experiments Niremberg conducted?
what was the significance of these finding?

A
  • found that the coding system was the same in many different organisms.
  • any organisms that shares the same coding system probably shares the same or common ancestor
42
Q

Protein synthesis

A
43
Q

what is a genome?

A

This is the complete set of
genes in a cell.

44
Q

what is a proteome?

A

This is the full range of proteins that a cell is able to produce.

45
Q

what is protein synthesis?

A

Protein synthesis involves the production of a chain of amino acids that forms the primary structure of a protein.
The sequence of amino acids are coded for by a gene.

46
Q

draw a word equation for protein synthesis

A

sequences of bases –(determines)–> sequences of amino acids in the polypeptide –(determines)–> shape and function of protein –(determines)–> characteristics of cell

47
Q

what is transcription?

A

the process of making pre-mRNA using part of the DNA as a template

48
Q

describe the full process of transcription.

A
  1. DNA helicase breaks down the hydrogen bonds on a specific region on DNA into 2 separate strands
  2. complimentary RNA nucleotides pair with the bases from one of the DNA strands called the template strand forming hydrogen bonds
  3. enzyme RNA polymerase then moves along the strand and joins the nucleotides together forming phosphodiester bonds
  4. pre-mRNA has been formed
  5. as the RNA polymerase adds the nucleotides one at a time to build pre-mRNA, the DNA strands re-join behind it
  6. when RNA polymerase reaches a particular sequence of bases on the DNA, it recognises a stop codon and detaches. the production of pre-mRNA is complete
49
Q

what is pre-mRNA spliced to form?

A

mRNA

50
Q

what are introns?

A

a section of DNA within a gene that does not code for amino acids

51
Q

what are extrons?

A

a section of DNA within a gene that does code for amino acids

52
Q

What are multiple repeats?

A

a section of repetitive DNA found outside of genes that do not code for amino acids

53
Q

What is splicing?

A

in order to produce functional proteins. A molecule called a spliceosome removes the introns, producing mature mRNA that contains only functional exons.

54
Q

how does mRNA leave the nucleus?

A

it diffuses out of the nuclear pore as it is too large

55
Q

explain the process of translation to produce a polypeptide

A
  • a ribosome becomes attached to the starting codon (AUG) at one end of the mRNA molecule
  • the tRNA molecule with the complementary anticodon sequence (UAC) moves to the ribosome and pairs up with the codon on the mRNA. this tRNA carries a specific amino acid methionine.
  • the tRNA molecule with a complimentary anticodon pairs with the next codon on the mRNA. the tRNA molecule carries another amino acid
  • the ribosome moves along the mRNA, bringing together two tRNA molecules at any one time, each pairing up with the corresponding two codons on the mRNA
  • the two amino acids (met and other) on the tRNA are joined by a peptide bond using an enzyme called (peptidyl transferase) and ATP which is hydrolysed to provide the required energy.
  • the ribosome moves onto the third codon in the sequence on the mRNA, thereby linking the amino acids on the second and third tRNA molecules
  • as this happens, the first tRNA is released from its’s amino acid (met) and is free to collect another amino acid from the amino acid pool in the cell
  • the process continues this way, with up to 15 amino acids being added each second, until a polypeptide chain ids built up
  • up to 50 ribosomes can pass immediately behind the first, so that many identical polypeptides can be assembled simultaneously
  • the synthesis of a polypeptide continues until a ribosome reaches a stop codon. at this point, the ribosome, the mRNA and the last tRNA molecule all separate and the polypeptide chain is complete
56
Q

what happens to the polypeptide after next?

A
  • made into a functional proteins
  • primary, secondary, tertiary or quaternary
57
Q

DONE

A

Biology Y12 (20 decks)

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