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A-level Biology > 2.1.3 - Nucleotides and nucleic acids > Flashcards

2.1.3 - Nucleotides and nucleic acids Flashcards

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1
Q

What is a nucleic acid ?

A

A large polymer formed from many nucleotides chemically joined together

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2
Q

What is a nucleotide composed of ?

A
  • A pentose sugar
  • A phosphate group
  • A nitrogenous base
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3
Q

Draw a diagram to display a nucleotide ?

A
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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
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5
Q

Name the bond that forms between nucleotides ?

A

A phosphodiester bond

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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

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7
Q

Draw a diagram to represent the formation of a phosphodiester bond between nucleotides ?

A
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8
Q

Name examples of nucleic acids ?

A
  • DNA
  • RNA
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9
Q

What are pyrimidines ?

A

Smaller bases which contain single carbon ring structures ( eg. cytosine and Thymine )

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10
Q

What are purines ?

A

Larger bases which contain double carbon ring structures ( eg. Adenine and Guanine )

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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
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12
Q

Draw a diagram to represent the structure of a deoxyribose sugar ?

A
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13
Q

Draw a diagram to represent the structure of a ribose sugar ?

A
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14
Q

What are the pyrimidines and purines of DNA nucleotides ?

A

Pyrimidines : Thymine ( T ) and Cytosine ( C )

Purines : Adenine ( A ) and Guanine ( G )

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15
Q

What is the function of DNA ?

A

DNA stores all the genetic information needed by an organism

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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
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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
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18
Q

What is complementary base pairing ?

A

The specific way in which the bases of two DNA polynucleotide strands bind

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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
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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

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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
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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
Q

Whatis the role of DNA polymerase in DNA replication ?

A

DNA polymerase catalyses the formation of phosphodiester bonds between nucleotides when free nucetodies pair with newly exposed bases of the replete strands

26
Q

Why do mutations occur ?

A
  • Sequences of bases are not always matched exactly leading to an incorrect sequence in newly copied strand
  • These errors occur randomly and spontaneously
27
Q

What is the effect of mutations ?

A

This leads to a change in the sequence of DNA bases

28
Q

Define the term ‘Genetic code’ ?

A

Genetic code - The sequence of bases in DNA are the ‘instructions’ for the sequences of amino acids in the production of proteins

29
Q

Define the term ‘Triplet code/codon’ ?

A

Codon - It is a sequence of three bases. Each codon codes for an Amino acid

30
Q

Explain why the genetic code is universal ?

A

It is universal since all organisms use the same code, although the sequences of bases coding for each individual protein will be different

31
Q

What is the degenerate code ?

A

Amino acids that can be coded for by more than one codon

32
Q

What are ‘start’ and ‘stop condones ?

A
  • 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
Q

Why are ‘start’ and ‘stop’ codons important ?

A

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
Q

Define the term ‘transcription’ ?

A

Transcription - The process of copying actions 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
Q

Describe the process of transcription in full detail ?

A

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
Q

What are ribosomes composed of ?

A

Ribosomes are mad up of proteins and ribosomal RNA

37
Q

What is the role of ribosomal RNA in protein synthesis ?

A
  • Ribosomal RNA maintains the structural stability of the protein synthesis sequence
  • It also catalyses the assembly of amino acids producing a polypeptide
38
Q

Define the term ‘translation’ ?

A

Translation - The process by which the complementary code carried by mRNA is decoded by tRNA into a sequence of amino acids

39
Q

What is tRNA / transfer RNA ?

A

It is a strand of RNA with an anticodon at one end of the molecule

40
Q

Explain the role of transfer RNA in protein synthesis/ translation ?

A
  • 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 propane coded for by mRNA
41
Q

Describe the process of translation in full detail ?

A

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
Q

What does ATP stand for ?

A

Adenosine triphosphate

43
Q

What is an ATP molecules composed of ?

A

An ATP molecule is composed of a nitrogenous base, a pentose sugar and three phosphate groups ( a phosphorylated nucleotide )

44
Q

What is the function of ATP ?

A

ATP molecules supply energy used for energy transfer

45
Q

Why do cells require energy ?

A
  • Synthesis
  • Transport
  • Movement/ muscle contraction
46
Q

Explain how ATP reactions lead to energy release ?

A
  • 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
Q

Describe the hydrolysis reaction of an ATP molecule ?

A

During the hydrolysis of ATP, a water molecule is used to hydrolyse ATP to ADP and a phosphate ion releasing energy

48
Q

Write the equation for the hydrolysis of ATP ?

A
49
Q

Describe the condensation reaction of ADP ?

A

During the condensation reaction, a water molecule is removed and a phosphate group is reattached to ADP resulting in an ATP molecule

50
Q

What does ADP stand for ?

A

Adenosine Diphosphate

51
Q

Explain why ATP is not a good long-term store ?

A

Due to the instability of the phosphate bonds in ATP, it is not a good long term store

52
Q

Explain why ATP is a good immediate energy store ?

A

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
Q

Draw a diagram to represent the structure of ATP ?

A

A-level Biology (30 decks)

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