Molecules and Cells > Nucleic Acids > Flashcards

Nucleic Acids Flashcards

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1
Q

give an overview on the structure of DNA

A
  • dna is found mainly in the nucleus
  • the backbone consists of deoxyriboses linked by phosphodiester bridges called bonds
  • the sugar of one nucleotide is joined at the hydroxyl group on carbon three to the phosphate group attached to carbon five of the sugar of the next nucleotide
  • the bases project laterally from the sugar residues
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2
Q

what is the 3’5’ phosphodiester bond

A

the bond between the OH group on 3’ of one sugar and the phosphate group on 5’ of the other sugar

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3
Q

give a breakdown on the structure of a single DNA strand

A
  • sugar phosphate backbone formed by the 3’5’ phosphodiester bonds
  • the double stranded structure that dna usually adopts is held together by hydrogen bonding between base pairs
  • two chains wound around each other to form a regular double helix
  • one strand is linked to another by base pairing
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4
Q

what direction is the double helix

A

it is right handed

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5
Q

how many bonds hold guanine and cytosine together

A

three bonds

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6
Q

how many bonds hold adenine and thymine together

A

two bonds

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7
Q

how are the two single dna strands held together

A

hydrogen bonding between the base pairs

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8
Q

give a breakdown on the general structure of RNA

A
  • rna is ribonucleic acid
  • it is found mainly in the cytoplasm
  • it has the same 5’3’ backbond as DNA
  • uracil replaces thymine in rna
  • the ribose replaces deoxyribose
  • it is single stranded, so no base pairing occurs
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9
Q

what is the exception to the no base pairing rule found in rna

A

hairpin loops, where there is local double strand formation occuring within DNA when there are stretches of bases that lie in close enough proximity to each other that they can form local double strands by the rna folding back on itself

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10
Q

what are the three types of rna

A

ribosomal rna
transfer rna
messenger rna

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11
Q

how much of the rna in the cell is composed of ribosomal rna

A

80%

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12
Q

what is used to measure the actual size of the rna

A

the sedimentary coefficient

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13
Q

what composition of the total RNA is made up by messenger RNA

A

5%

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14
Q

what composition of total RNA in a cell is made up by transfer RNA

A

15%

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15
Q

which form of RNA has a varying size when in animal cells

A

messenger RNA

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16
Q

what does the base sequence of DNA contain

A

genetic information in all cells known as the genetic code

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17
Q

what is the genetic code transmitted by

A

genes

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18
Q

what are genes

A

specific stretches of DNA that code for a protein

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19
Q

what are most of our characteristics coded by

A

our genes

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20
Q

what is the amino acid sequence of each protein determined by

A

the nucleotide sequence of its corresponding genes

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21
Q

what is the genome

A

the whole genetic information within a single cell nucleus

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22
Q

how is the order of nucleotides within DNA determined

A

they are ordered in such a way that they code for a specific sequence of amino acids

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23
Q

what are the different genomes you can find

A

viruses, bacteria and eukaryotes

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24
Q

what is an example of a virus genome and give its size

A

polyma and SV40 are both around 5100 bases in length

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25
give an example of bacteria and its size
e. coli which is 4000 bases long
26
give an example of some eukaryotic genomes and their size
yeast have 13,500 and drosophila have 165000 bases humans have 2.9 million bases
27
how are protein synthesised from dna
dna codes for the proteins, and we have to decipher the genetic message contained in DNA such that we have a protein made. this is done via the processes of transcription and translation
28
give a breakdown of transcription
- in the nucleus, dna unfolds (hydrogen bonds are split) to expose base pairs of the template strand - we now have two single strands of dna - rna polymerase copies sequences of bases in the template strand of dna to produce mrna - mrna is translated by trna using ribosomes as functional support in the cytoplasm
29
give a breakdown of translation
- each trna molecule carries an amino acid to the ribosome - there one specific trna molecule for each amino acids - amino acid is then transferred to the growing polypeptide chain - the sequence of mrna codons determines the sequence of amino acids in a protein
30
how are do trna molecules join the amino acids
each trna molecule contains an anticodon which is a sequence of three bases which is complementary to a sequence of three bases called a codon on the mrna
31
how many transfer rnas are encoded by a triplet code
up to 64
32
how many amino acids are there
20
33
can some amino acids have more than one trna
yes
34
which codons code for phenyl alanine
uuu and uuc
35
how many different codons does serine have
six
36
what does it mean to say that genetic code is degenerate
multiple codons that code for the same amino acid
37
how do the degenerate codons differ
by the third base position - they are usually grouped together
38
how does protein synthesis start
every protein has a start codon which signals for synthesis to begin. the start codon AUG codes for methionine.
39
how does protein synthesis get terminated
there are signals to terminate protein synthesis known as stop codons. they are UAA, UGA, UAG.
40
what are ribosomes
organelle with small and large subunits that contain proteins and rrna
41
how many codons code for the 20 amino acids
64
42
what are mutations
permament alteration in dna (gene sequences)
43
what are the possible causes for mutations
errors in dna synthesis that occur spontaneously at low frequencies chemical mutagens ionising radiation single base mutations that may have effects of varying degrees of severity order of base changes insertion, deletion and altered bases
44
what are the different types of subsitution mutation
conservative and non conservative, and no mutation
45
what is a conservative amino acid substition
the amino acid is replaced by another with similar properties
46
what is a non conservative subsitution
this is when the amino acid is replaced by another with different properties
47
what is a no mutation substution mutation
this is when there is a change in the third position of the codon but it does not change the amino acid that it codes for because it is a degenerative codon
48
what are the possible effects of mutations on the protein being synthesised
- the protein could have premature termination and be shorter - could be an entirely different protein - could be a normal functional protein - could be a single amino acid change - there could be no change
49
what can cause a premature or delayed stop codon
the frameshift caused by the insertion or deletion of a base can lead to synthesis of a protein that has a completely different sequence downstream of the mutation. and if a stop codon is included in this it can lead to it being premature if one is inserted, or delayed if one is deleted
50
what is sickle cell anaemia caused by
single base substitution in the beta chain of haemoglobin which replaces glutamic acid with valine, which is a non conservative mutation. the substitution is GAG to GTG
51
what are some more drastic mutations that can occur
deletion or duplication of longer stretches of DNA
52
why is it good that hydrogen bonds join the two base pairs together to form the double helix of dna
they are weaker than covalent bonds, and can be easily broken and reformed. this is useful during transcription and in cell division
53
what is a polynucleotide chain
this is a string of nucleotides one after another
54
what are the two strands that make up the double helix of dna called
polynucleotides
55
give a breakdown on histone proteins and their function
these are proteins usually found in groups of eight called nucleosomes, that the dna wraps twice around.
56
how do dna attach to nucleosomes
the nucleosomes are positively charged and the phosphate group on the dna are negatively charged, so the opposite attract.
57
what are chromatin fibres
these are groups of nucleosomes that can fall into two different groups; eurochromatine and heterochromatin
58
what are eurochromatin fibres
these are where the groups of nucleosomes are loosely packed together, and this is becuase they contain genes that the cell frequently uses and needs access to
59
what are heterochromatin fibres
these are nucleosomes that are more densely packed, and they contain genes the cell rarely uses, if ever.
60
what do nucleosomes package together to form
chromatin fibres
61
what are the bases on the dna structure also sometimes referred to as
nitrogenous bases
62
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