2.1.3 - Nucleotides and nucleic acids Flashcards
1
Q
What is a nucleic acid ?
A
A large polymer formed from many nucleotides chemically joined together
2
Q
What is a nucleotide composed of ?
A
- A pentose sugar
- A phosphate group
- A nitrogenous base
3
Q
Draw a diagram to display a nucleotide ?
A
4
Q
Describe what happens during a condensation reaction between nucleotides ?
A
- During a condensation reaction, many nucleotides are chemically joined form a polynucleotide
- A covalent bond called a phosphodiester bond forms between the phosphate group at carbon 5 of one nucleotide and a hydroxyl group at carbon 3 of another
5
Q
Name the bond that forms between nucleotides ?
A
A phosphodiester bond
6
Q
Describe what happens during a hydrolysis reaction of a polynucleotide ?
A
During a hydrolysis reaction, the phosphodiester bond is broken resulting in individual nucleotides
7
Q
Draw a diagram to represent the formation of a phosphodiester bond between nucleotides ?
A
8
Q
Name examples of nucleic acids ?
A
- DNA
- RNA
9
Q
What are pyrimidines ?
A
Smaller bases which contain single carbon ring structures ( eg. cytosine and Thymine )
10
Q
What are purines ?
A
Larger bases which contain double carbon ring structures ( eg. Adenine and Guanine )
11
Q
What are the differences in the structure of DNA and RNA nucleotides ?
A
- DNA nucleotides contain a deoxyribose sugar while RNA nucleotides contain a ribose sugar
- DNA nucleotides contain the bases Thymine, Cytosine, Adenine and Guanine while RNA nucleotides contain the bases Uracil, Cytosine, Adenine and Guanine
12
Q
Draw a diagram to represent the structure of a deoxyribose sugar ?
A
13
Q
Draw a diagram to represent the structure of a ribose sugar ?
A
14
Q
What are the pyrimidines and purines of DNA nucleotides ?
A
Pyrimidines : Thymine ( T ) and Cytosine ( C )
Purines : Adenine ( A ) and Guanine ( G )
15
Q
What is the function of DNA ?
A
DNA stores all the genetic information needed by an organism
16
Q
What is the function of RNA ?
A
- DNA is a very long molecule and is therefore unable to leave the nucleus to reach sires of protein synthesis/ supply information
- RNA is responsible for transferring genetic information from DNA to site of protein synthesis
- A short section of the DNA molecule corresponding to a single gene is transcribed into a shorter messenger RNA molecule
- RNA polymers are small enough to leave the nucleus
17
Q
Explain the structure of a ‘double helix’ ?
A
- A double helix is made up of two strands of antiparallel DNA polynucleotides joined together by hydrogen bonds between complimentary base pairs
- This causes the strands to coil/twist around each other forming a double helix shape
18
Q
What is complementary base pairing ?
A
The specific way in which the bases of two DNA polynucleotide strands bind
19
Q
Why are there complementary base pairings ?
A
- Adenine and Thymine are able to form two hydrogen bonds while Guanine and Cytosine are able to form three hydrogen bonds
- This means that a small pyrimidine base will always binds to a larger purine base
- Therefore, there is a constant distance between the DNA ‘backbones’ resulting in parallel nucleotide chains
20
Q
Define the term ‘DNA replication’ ?
A
The process by which the two strands of DNA double helix separate and each strand serves as a template to produce a new double-stranded DNA molecule
21
Q
What is semi-conservative replication ?
A
- When the two strands separate, hydrogen bonds are broken between complementary bases
- Free DNA nucleotides then pair with complementary bases and hydrogen bonds form
- Nucleotides join to adjacent nucleotides with phosphodiester bonds
- This leads to two new molecules of DNA being produced each made of one new and old strand so called semi-conservative replication
22
Q
What is DNA replication controlled by ?
A
Enzymes
23
Q
What are the two main enzymes involved in DNA replication ?
A
- DNA helicase
- DNA polymerase
24
Q
What is the role of DNA helicase in DNA replication ?
A
- The operating of the two DNA strands is carried out by DNA helicase
- It catalyses reactions that breaks the hydrogen bonds between complementary base pairs causing the double helix to unzip
25
Whatis the role of DNA polymerase in DNA replication ?
DNA polymerase catalyses the formation of phosphodiester bonds between nucleotides when free nucetodies pair with newly exposed bases of the replete strands
26
Why do mutations occur ?
- Sequences of bases are not always matched exactly leading to an incorrect sequence in newly copied strand
- These errors occur randomly and spontaneously
27
What is the effect of mutations ?
This leads to a change in the sequence of DNA bases
28
Define the term 'Genetic code' ?
Genetic code - The sequence of bases in DNA that are the 'instructions' for the sequences of amino acids in the production of proteins
29
Define the term 'Triplet code/codon' ?
Codon - It is a sequence of three bases. Each codon codes for an Amino acid
30
Explain why the genetic code is universal ?
It is universal since all organisms use the same code, although the sequences of bases coding for each individual protein will be different
31
What is the degenerate code ?
Amino acids that can be coded for by more than one codon
32
What are 'start' and 'stop condones ?
- There are 'start' codons that come at a beginning of a gene and 'stop' codons which come at the end
- 'Start' codons signal the start of sequence that codes for a protein and 'stop' codons do not ode for any amino acids and signal the end of a sequence
33
Why are 'start' and 'stop' codons important ?
They ensure codons are read 'in frame' and that DNA base sequence is 'read' from base 1 instead of 2/3
- This ensures genetic code is non-overlapping
34
Define the term 'transcription' ?
Transcription - The process of copying sections of DNA base sequence to produce smaller molecules of mRNA ( which can be transported out of the nucleus via nuclear pores to the site of protein synthesis )
35
Describe the process of transcription in full detail ?
1 ) The section of DNA contains the gene unzips when DNA helicase catalyses the breakage of hydrogen bonds between the bases
2 ) One strand contains the code for the protein - sense strand
3 ) The other strand is a complementary copy of the sense strand and does not code for protein - antisense strand
4 ) The antisense strand acts as a template strand, so complementary RNA strand formed carries the same base sequence as sense strand which codes for a protein
5 ) Free RNA nucleotides will base pair with complementary base of template strand ( A-U and C-G )
6 ) RNA polymerase will catalyse the formation of phosphodiester bonds between RNA nucleotides
7 ) Transcription stops at the end of the gene producing a short strand of RNA called mRNA
8 ) The mRNA detaches from the DNA template, leaves the nucleus via the nuclear pore and travels to the ribosomes/ sire of protein synthesis
36
What are ribosomes composed of ?
Ribosomes are mad up of proteins and ribosomal RNA
37
What is the role of ribosomal RNA in protein synthesis ?
- Ribosomal RNA maintains the structural stability of the protein synthesis sequence
- It also catalyses the assembly of amino acids producing a polypeptide
38
Define the term 'translation' ?
Translation - The process by which the complementary code carried by mRNA is decoded by tRNA into a sequence of amino acids
39
What is tRNA / transfer RNA ?
It is a strand of RNA with an anticodon at one end of the molecule
40
Explain the role of transfer RNA in protein synthesis/ translation ?
- The anticodon binds to a complementary codon on mRNA and tRNA carries an amino acid corresponding to that codon
- The amino acids are brought together in the correct sequence to format he primary structure of the protein coded for by mRNA
41
Describe the process of translation in full detail ?
1 ) The mRNA binds to the small subunit of the ribosome at its start codon
2 ) A tRNA with a complementary anticodon binds to mRNA Strat codon. The tRNA simultaneously carries the amino acid complementary anticodon
3 ) Another tRNA with a complementary anticodon for the following codon ( carrying the corresponding amino acid ) binds to the next codon on the mRNA
4 ) The first amino acid is transferred to the amino acid on the second tRNA by the formation of a peptide bond which is catalysed by rRNA
5 ) The ribosome moves along the mRNA, releasing the first tRNA so the second becomes the first
6 ) This is repeated till ribosome reaches the end of the mRNA at a stop codon and polypeptide is released
42
What does ATP stand for ?
Adenosine triphosphate
43
What is an ATP molecules composed of ?
An ATP molecule is composed of a nitrogenous base, a pentose sugar and three phosphate groups ( a phosphorylated nucleotide )
44
What is the function of ATP ?
ATP molecules supply energy used for energy transfer
45
Why do cells require energy ?
- Synthesis
- Transport
- Movement/ muscle contraction
46
Explain how ATP reactions lead to energy release ?
- A small amount of energy is needed to break weak bonds holding last phosphate group to ATP producing ADP and liberated phosphate
- A large amount of energy is released when the liberated phosphate undergoes other reactions involving bond formation
- Overall, more energy is released as little energy is needed to break bone but more energy is released when bonds form
47
Describe the hydrolysis reaction of an ATP molecule ?
During the hydrolysis of ATP, a water molecule is used to hydrolyse ATP to ADP and a phosphate ion releasing energy
48
Write the equation for the hydrolysis of ATP ?
49
Describe the condensation reaction of ADP ?
During the condensation reaction, a water molecule is removed and a phosphate group is reattached to ADP resulting in an ATP molecule
50
What does ADP stand for ?
Adenosine Diphosphate
51
Explain why ATP is not a good long-term store ?
Due to the instability of the phosphate bonds in ATP, it is not a good long term store
52
Explain why ATP is a good immediate energy store ?
ATP is rapidly reformed by the phosphorylation of ADP so ATP is a good immediate energy store and ells do not need to store a lot of it
53
Draw a diagram to represent the structure of ATP ?
