2.1.3 - Nucleotides and nucleic acids Flashcards
What is a nucleic acid ?
A large polymer formed from many nucleotides chemically joined together
What is a nucleotide composed of ?
- A pentose sugar
- A phosphate group
- A nitrogenous base
Draw a diagram to display a nucleotide ?
Describe what happens during a condensation reaction between nucleotides ?
- 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
Name the bond that forms between nucleotides ?
A phosphodiester bond
Describe what happens during a hydrolysis reaction of a polynucleotide ?
During a hydrolysis reaction, the phosphodiester bond is broken resulting in individual nucleotides
Draw a diagram to represent the formation of a phosphodiester bond between nucleotides ?
Name examples of nucleic acids ?
- DNA
- RNA
What are pyrimidines ?
Smaller bases which contain single carbon ring structures ( eg. cytosine and Thymine )
What are purines ?
Larger bases which contain double carbon ring structures ( eg. Adenine and Guanine )
What are the differences in the structure of DNA and RNA nucleotides ?
- 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
Draw a diagram to represent the structure of a deoxyribose sugar ?
Draw a diagram to represent the structure of a ribose sugar ?
What are the pyrimidines and purines of DNA nucleotides ?
Pyrimidines : Thymine ( T ) and Cytosine ( C )
Purines : Adenine ( A ) and Guanine ( G )
What is the function of DNA ?
DNA stores all the genetic information needed by an organism
What is the function of RNA ?
- 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
Explain the structure of a ‘double helix’ ?
- 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
What is complementary base pairing ?
The specific way in which the bases of two DNA polynucleotide strands bind
Why are there complementary base pairings ?
- 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
Define the term ‘DNA replication’ ?
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
What is semi-conservative replication ?
- 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
What is DNA replication controlled by ?
Enzymes
What are the two main enzymes involved in DNA replication ?
- DNA helicase
- DNA polymerase
What is the role of DNA helicase in DNA replication ?
- 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
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
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
What is the effect of mutations ?
This leads to a change in the sequence of DNA bases
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
Define the term ‘Triplet code/codon’ ?
Codon - It is a sequence of three bases. Each codon codes for an Amino acid
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
What is the degenerate code ?
Amino acids that can be coded for by more than one codon
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
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
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 )
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
What are ribosomes composed of ?
Ribosomes are mad up of proteins and ribosomal RNA
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
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
What is tRNA / transfer RNA ?
It is a strand of RNA with an anticodon at one end of the molecule
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
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
What does ATP stand for ?
Adenosine triphosphate
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 )
What is the function of ATP ?
ATP molecules supply energy used for energy transfer
Why do cells require energy ?
- Synthesis
- Transport
- Movement/ muscle contraction
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
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
Write the equation for the hydrolysis of ATP ?
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
What does ADP stand for ?
Adenosine Diphosphate
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
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
Draw a diagram to represent the structure of ATP ?
