nucleotides Flashcards
1
Q
what are nucleotides made from?
A
- a pentose sugar (with 5 carbon atoms)
- a nitrogenous base
- a phosphate group
2
Q
what elements do nucleotides contain?
A
- CHONP - carbon, hydrogen, oxygen, nitrogen phosphorus
3
Q
why are nucleotides important?
A
- they are the monomers that make up DNA and RNA which are both types of nucleic acid.
4
Q
what is DNA used for?
A
- to store genetic information
5
Q
what is RNA used for?
A
- to make proteins from the instructions in DNA
6
Q
what are the pentose sugars in DNA called?
A
- deoxyribose
7
Q
what is the structure of DNA?
A
- deoxyribose, a phosphate group and a base
8
Q
what are the two purines?
A
- Adenine
- Guanine
9
Q
what are the two pyramidines?
A
- Cytosine
- Thymine ( and uracil in RNA)
10
Q
what is a purine?
A
- a base containing two carbon-nitrogen rings joined together
11
Q
what is a pyramidine?
A
a base that only has one carbon-nitrogen ring
12
Q
which base is smaller? purine or pyramidine
A
- pyrimidine
13
Q
what is the sugar in RNA called?
A
- ribose
14
Q
what is the structure of RNA?
A
- ribose, a phosphate group and one of four bases
15
Q
how many nucleotide chains are found in RNA?
A
- one
16
Q
how many nucleotide chains are found in DNA?
A
- two
17
Q
what are phosphorylated nucleotides?
A
- a nucleotide with one or more phosphate groups added to it
- for example ADP and ATP
18
Q
describe ATP
A
- provides energy for chemical reactions in the cell
- a phosphorylated nucleotide
- synthesized from ADP and an inorganic phosphate
- contains a phosphate bond where energy is stored and released when required by breaking the bond
19
Q
what do nucleotides form to create?
A
polynucleotides
20
Q
what is the chain of sugars and phosphates known as?
A
the sugar phosphate backbone
21
Q
how are polynucleotides broken down?
A
by hydrolysis of the phosphodiester bonds
22
Q
how do nucleotides join up?
A
they join up through the phosphate group of one nucleotide and the sugar of another via a condensation reaction
23
Q
how do two polynucleotide strands join together?
A
hydrogen bonding between the bases
24
Q
how many bonds form between adenine and thymine?
A
two
25
how many bonds form between cytosine and guanine
three
26
how many polynucleotide strands twist to form the DNA double helix?
two antiparallel polynucleotide
27
how can you purify DNA?
using a precipitation reaction
28
how do you carry out a precipitation reaction to purify DNA?
1. Break up the cells using a blender
2. Add the cells to a detergent solution containing salt and distilled water and leave in a water bath at 60° for 15 minutes
3. Put the beaker in an ice bath to cool down
5. Filler the mixture
6. As protease enzymes
7. Dribble some ice cold ethanol down the side of the tube so it forms a layer on top of the detergent DNA mixture
8. Leave for a minute and a white precipitation will form which you can remove with a glass rod
29
What do protease enzymes do?
break down proteins
30
What do RNase enzymes do?
Break down RNA
31
Why does DNA copy itself before cell division?
so that each cell has the full amount of DNA
32
what happens in stage one of cell self-replication?
DNA delicate breaks the hydrogen bonds between the two polynucleotide DNA strands, and the helix unzips to form two single strands
33
What does DNA helicase do?
Breaks the hydrogen bonds between the two polynucleotide DNA strands
34
What happens in stage two of DNA self-replication?
Each original stand acts as a template for a new stand. Free floating DNA nucleotides join to the exposed bases on each original template strand by complementary base pairing
35
What happens in stage three of DNA self replication?
The polynucleotides of the new strand are joined together by the enzyme DNA polymerase which forms the sugar phosphate backbone. Hydrogen bond’s form between the bases on the original and the new strand and twist to form a double helix.
36
What does DNA polymerase do?
Joins nucleotides together forming the sugar phosphate backbone.
37
What happens in stage four of DNA’s self replication?
Each new DNA molecule contains one strand from the original DNA molecule and one new strand
38
What is semi-conservative replication?
When half of the strands in each new DNA molecule are from the original piece of DNA. The new molecule contains one new strand and one old strand.
39
What is a mutation?
A change in the DNA base sequence.
40
What can mutations do?
Can alter the sequence of amino acids in a protein, causing an abnormal prison to be produced. This abnormal protein may function better or not function at all.
41
What does DNA contain that helps it make proteins?
Genes
42
What is a gene?
A gene is a sequence of DNA nucleotides that codes for a polypeptide. This forms the primary structure of a protein
43
What does the order of nucleotide bases determine?
The order of amino acids in a particular protein
44
What is each amino acid coded for by?
A sequence of three bases ( a triplet) in a gene. Different sequences of bases code for different amino acids. The sequence of bases in a section of DNA is a template that’s used to make proteins during protein synthesis.
45
Where are DNA molecules found?
At the nucleus
46
Where are the organelles that make proteins found?
At the ribosomes which are found in the cytoplasm
47
Why is a section of DNA copied onto mRNA?
It’s to large to move out of the nucleus
48
What is transcription?
When a section of DNA is copied onto mRNA
49
What is translation?
When mRNA leaves the nucleus and joins with a ribosome in the cytoplasm where it can be used to synthesise a protein
50
What is it called when mRNA leaves the nucleus and joins with a ribosome in the cytoplasm where it can be used to synthesise a protein?
Translation
51
What is it called when a section of DNA is copied into mRNA ?
Transcription
52
What are the three types of DNA?
• messenger RNA (mRNA)
• transfer RNA (tRNA)
• ribosomal RNA (rRNA)
53
Describe messenger RNA (mRNA)
• made in the nucleus
• three adjacent bases called a codon
• it carries the genetic code from the DNA in the nucleus to the cytoplasm where it’s used to make a protein during translation
54
Describe transfer RNA (tRNA)
• found in the cytoplasm
• it has an amino acid binding site at one end and a sequence of thee bases at the other end called an anticodon
• it carries the amino acids that are used to make proteins to the ribosomes during translation
55
Describe ribosomal RNA (rRNA)
• forms the two subunits in a ribosome (along with proteins)
• the ribosome moves along the mRNA strand during protein synthesis. The rRNA in the ribosome helps to catalyse the formation of peptide bonds between the two amino acids
56
What are the three features of DNA?
• non overlapping
• degenerate
• universal
57
What is the genetic code?
The sequence of base triplets ( codons ) in DNA or mRNA which codes for specific amino acids
58
What does non overlapping mean?
Each base triplet in the genetic code is read in sequence, separate from the triplet before and after it. Base triplets don’t share their bases - the code is non-overlapping.
59
What does degenerate mean?
There are more possible combinations of triplets than there are amino acids (20 amino acids, 64 triplets) this means that some amino acids are coded for by more than one base triplet, e.g triosene which can be coded for by UAU or UAC
60
What are start and stop signals/codons?
They are found at the beginning and the end of the gene and are used to tell the cell to start and stop production of the protein.
61
What does universal mean?
The same specific base triplets code for the same amino acids in all living things
62
What is the first stage of protein synthesis?
Transcription?
63
When does transcription start?
When RNA polymerase attaches to the DNA double helix at the beginning of a gene, the hydrogen bonds between the two strands in the gene break which separates the strands ands the DNA molecule uncoils. One of the strands is used as a template to make an mRNA copy.
64
What does RNA polymerase do?
Attaches to the double helix and breaks the hydrogen bonds between the two strands
65
What does RNA polymerase do in the second stage of transcription?
It lines up free RNA nucleotides alongside the template strand. Complementary base pairing means that the mRNA strand ends up being a complementary copy of the DNA template strand.
66
What does RNA polymerase do?
Lines up free nucleotides alongside the template strand in transcription
67
What happens during transcription when RNA nucleotides have paired up with their specific bases?
They form an mRNA molecule, and then a strand which reforms hydrogen bonds and could back into a a double helix
68
What happens during transcription when RNA polymerase reaches a stop codon?
It stops making RNA and detaches from the DNA. The mRNA then moves out of the nucleus through a nuclear pore and attaches to a ribosome in the cytoplasm where the next stage takes place
69
What enzyme is used in transcription?
• RNA polymerase
70
Briefly outline transcription
1. RNA polymerase attaches to the DNA double helix
2. The hydrogen bonds between the two DNA strands in the gene break separating them and causing the helix to uncoil
3. One of the strands is used as a template copy
4. RNA polymerase lines up free RNA nucleotides alongside the template strand and complementary base pairing occurs
5. Once the nucleotides have paired up they are joined together forming an mRNA molecule
6. Hydrogen bonds reform and coil back into a double helix
7. The stop codon is reached and so mRNA stops producing and RNA polymerase detaches from the DNA
8. The mRNA moves it off the nucleus and attaches to a ribosome in the cytoplasm causing translation
71
What is the second stage of protein synthesis called?
Translation
72
Where does translation occur?
At the ribosome in the cytoplasm
73
What happens to amino acids in translation?
They join to make a polypeptide chain (protein) following the sequence of codons carried by the mRNA
74
What happens in translation?
1. The mRNA attaches itself to the ribosome and tRNA molecules carry amino acids to the ribosome
2. A tRNA molecule with an anticodon that’s complementary to the start codon on the mRNA starches itself to the mRNA through complementary bases pairing.
3. A second tRNA molecule attaches itself to the next codon on the mRNA strand the same way.
4. Ribosomal RNA catalyses the formation of a peptide bond between two amino acids which joins them together, and the first one moves away leaving another behind.
5. A third tRNA molecule bonds to the next codon on the mRNA and this process continues until there a stop codon.
6. The polypeptide chain moves away from the ribosome and translation is complete.
