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A - Biology > Topic 4A - DNA, RNA and protein synthesis ARN * > Flashcards

Topic 4A - DNA, RNA and protein synthesis ARN * Flashcards

DNA, genes and chromosomes RNA and protein synthesis the genetic code and nucleic acids

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1
Q

what kind of DNA do eukaryotic cells contain?

A

linear DNA molecules in the form of chromosomes, thread-like structures, each made up of one long molecule of DNA, found in the nucleus

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2
Q

how are chromosomes structured to fit inside the nucleus of a eukaryotic cell?

A

long DNA molecule wound up so it can fit in the nucleus
its wound around proteins called histones
its then coiled very tightly to make a compact chromosome

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3
Q

what do histone proteins do?

A

they help support the DNA

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4
Q

what is DNA inside chloroplast and mitochondria like?

A

they have their own DNA, which is similar to prokaryotic data because its circular and shorter and not associated with histone proteins

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5
Q

what is DNA like in prokaryotic cells?

A

they carry DNA as chromosomes, but the DNA molecules are shorter and circular
the DNA isn’t wound into histones, it condenses by supercoiling

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6
Q

what is a gene?

A

a section of DNA bases that codes for the sequence of amino acids in a polypeptide or functional RNA

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7
Q

what forms the primary structure of a protein?

A

the sequence of amino acids

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8
Q

what determines the order of amino acids in a polypeptide?

A

the order of bases in a gene determines the primary structure, different polypeptides have different numbers and orders of amino acids

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9
Q

what codes for each amino acid?

A

a sequence of 3 bases in a gene called a triplet or codon codes for an amino acid

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10
Q

what is the first stage of protein synthesis?

A

DNA is 1st copied into messenger RNA

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11
Q

what do genes code for if not for a polypeptide?

A

genes that don’t code for a polypeptide code for functional RNA instead

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12
Q

what is functional RNA?

A

RNA molecules other than mRNA, which perform special tasks during protein synthesis e.g. tRNA and ribosomal RNA, which forms part of ribosomes

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13
Q

what is a genome?

A

a cell’s genome is the complete set of genes in the cell.

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14
Q

what is a proteome?

A

a cell’s proteome is the full range of proteins that the cell is able to produce

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15
Q

what are introns?

A

sections of DNA in a gene that don’t code for amino acids

only in eukaryotes

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16
Q

what are coding parts of a gene called?

A

exons

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17
Q

what happens to introns?

A

they’re removed in protein synthesis in a process called splicing- so they don’t affect the amino acid order

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18
Q

what are non-coding repeats?

A

eukaryotic data contains regions of multiple repeats outside of genes. these are DNA sequences that repeat over and over and don’t code for amino acids either

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19
Q

what are the different forms of a gene called?

A

alleles

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20
Q

how are alleles different?

A

the order of bases in each allele is slightly different, so they code for slightly different versions of the same polypeptide

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21
Q

how many chromosomes do humans have?

A

23 pairs, 46 in total. pairs of matching chromosomes are called homologous pairs

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22
Q

what are homologous pairs?

A

chromosomes that are the same size and have the same genes, but they could have different alleles. alleles coding for the same characteristic are found at the same locus.
we inherit 1 allele from each parent

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23
Q

what is a locus?

A

a fixed position on each chromosome in a homologous pair. the location of a gene on the strand of DNA/ chromosome

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24
Q

what happens to DNA when a protein is demand?

A

the DNA is separated so the genetic code can be ‘read’
only one strand is read the other is just to protect the bases
the base sequence provides the instructions for a proteins primary structure

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25
Q

how many different possible codons are there?

A

64
4 bases with 3 different positions for them to be in
so 4^3

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26
Q

what are the features of the genetic code?

A 
degenerate
each codon read from 5' to 3'
every gene begins with TAC
there are 3 different 'stop' codons that signify the end of a gene
non-overlapping
universal
27
Q

what are the differences between eukaryotic and prokaryotic DNA?

A 
eukaryotes - very long
-many molecules of DNA
-no plasmids
-linear
-chromosomes
-associated with proteins (histones)
prokaryotes - shorter
-1 main piece of DNA
-plasmids
-ring structure
-no chromosomes
-not associated with histones
28
Q

what form is DNA in within the nucleus?

A

in the nucleus of a resting cell DNA exists in the form of chromatin

29
Q

when is DNA in chromosome form?

A

after DNA replication occurs and 2 strands of semi-conserved daughter DNA are produced. they are connected at the centromere and referred to as sister chromatids, at this point they need to be condensed into the packaged form of a chromosome (during prophase)

30
Q

what is the diploid number?

A

the total of the homologous pairs

31
Q

what is the haploid number?

A

half the diploid number

32
Q

how do new alleles arise?

A

as a result of random mutations

33
Q

what are the different types of RNA?

A

messenger RNA

transfer RNA

34
Q

when is mRNA made?

A

during transcription

35
Q

what is mRNA?

A

a single polynucleotide strand, groups of 3 adjacent bases are called codons

36
Q

what does mRNA do?

A

it carries the genetic code from the DNA to the ribosomes, where it’s used to make a protein during translation

37
Q

what does tRNA do?

A

it carries the amino acids that are used to make proteins to the ribosomes in translation

38
Q

what is tRNA?

A

a single polynucleotide strand that’s folded into a clover shape. hydrogen bonds between specific base pairs hold the molecule in this shape

39
Q

what does every tRNA molecule contain?

A

a specific sequence of 3 bases at one end called an anticodon
and an amino acid binding site at the other end

40
Q

what is the first stage of protein synthesis?

A

transcription

41
Q

when does transcription start?

A

when RNA polymerase attaches to the DNA double-helix at the beginning of a gene

42
Q

what happens in transcription?

A 
DNA strands separated by breaking H bonds
1 strand used as template strand
complementary base pairing occurs
RNA polymerase lines up free RNA nucleotides and joins them
DNA re-coils into double helix
RNA polymerase reaches stop signal 
splicing
mRNA leaves nucleus
43
Q

how is the DNA strand separated for transcription?

A

the hydrogen bonds between 2 DNA strands in gene are broken by DNA helicase attached to RNA polymerase. this separates strands, uncoiling DNA molecule and exposing bases

44
Q

how are free RNA nucleotides lined up in transcription?

A

free RNA nucleotides are attracted to exposed bases. specific, complementary base pairing means mRNA strand is complementary copy of template strand

45
Q

how is mRNA formed in transcription?

A

RNA polymerase joins up RNA nucleotides after they’re paired with bases on template strand, forming mRNA molecule
the RNA polymerase then moves along DNA, separating strands and assembling mRNA strand

46
Q

how does double-helix re-coil?

A

hydrogen bonds between uncoiled strands of DNA re-form once the RNA polymerase has passed, and the strands coil back into a double-helix

47
Q

in eukaryotes, what happens when RNA polymerase reaches a ‘stop signal’?

A

it stops making RNA and detaches from the DNA.

the mRNA moves out of nucleus through nuclear pore and attaches to a ribosome in the cytoplasm

48
Q

what is a ‘stop signal’?

A

a particular sequence of DNA that tell RNA polymerase to stop making RNA

49
Q

how is pre-mRNA formed?

A

introns and exons are both copied into mRNA during transcription
this is called pre-mRNA

50
Q

what happens to pre-mRNA after transcription?

A

splicing occurs - removing introns and joining exons - forming mRNA
this takes place in the nucleus before it leaves for the next stage of protein synthesis

51
Q

how does transcription in prokaryotes differ from eukaryotes?

A

mRNA is produced directly from the DNA - without splicing taking place
(there are no introns in prokaryotic DNA)

52
Q

where does translation occur?

A

at the ribosomes in the cytoplasm

53
Q

what happens in translation?

A 
mRNA attaches to ribosome
tRNA with amino acids attaches to mRNA
amino acids joined together
this repeats until stop signal reached
polypeptide chain now formed
54
Q

how does tRNA bring amino acids to ribosome?

A

ATP provides energy for bonds to form between amino acid and tRNA
tRNA with an anticodon complementary to mRNAs codon attaches to mRNA via specific base pairing
bringing amino acid with it

55
Q

how are amino acids joined together at ribosomes?

A

2 tRNA molecules attach to codons on mRNA
their amino acids are joined by a peptide bond
1st tRNA leaves and a 3rd one binds to the next codon
its amino acid is bonded to the 2nd one then the 2nd tRNA leaves and so on

56
Q

exam technique for transcription:

A 
DNA strands separate by breaking H bonds
only template strand used to make RNA
complementary base pairing occurs
adjacent RNA nucleotides joined by RNA polymerase
pre-mRNA formed
splicing/ introns removed to form mRNA
57
Q

differences between DNA and mRNA?

A 
DNA             -             RNA
double stranded - single stranded
very long       -       short
thymine        -        uracil
deoxyribose    -    ribose
base pairings/hydrogen bonding - no base pairings/ hydrogen bonding
has introns     -     no introns
58
Q

translation exam technique:

A 
mRNA associates with ribosome
ribosome moves to start codon
tRNA brings a specific amino acid
anticodon complementary to codon
ribosome moves to next codon
process repeated and amino acids joined by peptide bonds to form polypeptide
59
Q

differences between mRNA and tRNA?

A

mRNA - tRNA
longer/ has more nucleotides - shorter
straight molecule - clover-leaf shaped
no base pairings/hydrogen bonds - some base pairings/ hydrogen bonds
no amino acid binding site - amino acid binding site
many different mRNA - only 20/64 tRNA’s
no anticodon - anticodon

60
Q

what is the genetic code?

A

the sequence of base triplets in mRNA which code for specific amino acids

61
Q

what does it mean that the genetic code is non-overlapping?

A

each base triplet is read in sequence, separate from before it and after it
base triplets don’t share their bases

62
Q

what does it mean that the genetic code is degenerate?

A

there are more possible combinations of triplets than there are amino acids. this means that some amino acids are coded for by more than one base triplet

63
Q

what does it mean that the genetic code is universal?

A

the same specific base triplets code for the same amino acids in all living things

A - Biology (21 decks)

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