Module 2.1.3 Nucleotides & Nucleic Acids Flashcards
What are the 2 types of nucleic acid?
DNA (deoxyribonucleic acid) & RNA (ribonucleic acid)
Why are nucleic acids vital molecules?
They carry the genetic code for all living things
What elements do nucleic acids contain?
Carbon, hydrogen, oxygen, nitrogen & phosphorus (CHONP)
What is a polynucleotide?
A molecule made of many nucleotide monomers joined by covalent bonds
What is a nucleotide?
A biological molecule that participates in nearly all biochemical processes.
They form the monomers of nucleic acids (DNA & RNA) & they help regulate metabolic pathways
What does it mean when a nucleotide becomes phosphorylated?
When a nucleotide contains more than 1 phosphate group (ADP & ATP)
What is the structure of a nucleotide?
A pentose sugar molecule (either ribose/deoxyribose)
An organic nitrogenous base (Adenine, Cytosine, Thymine, Guanine & Uracil)
A phosphate group
What is an organic nitrogenous base?
A nitrogen-containing organic compound that is a constituent of nucleotides (there’s 5)
What is the difference between a ribose & deoxyribose pentose sugar?
Ribose has 2 OH molecules
Deoxyribose has 1 OH molecule
Which bases are present in DNA nucleotides?
Adenine
Thymine
Cytosine
Guanine
Which bases are present in RNA nucleotides?
Adenine
Uracil
Cytosine
Guanine
What is a pyrimidine?
A smaller base that contains a single carbon ring structure
Which bases are pyrimidines?
Thymine, Uracil & Cytosine
What is a purine?
A larger base that contains a double carbon ring structure
Which bases are purines?
Adenine & Guanine
Why do we need energy?
Synthesis -> to build large complex molecules from smaller ones
Transport -> active transport
Movement -> protein muscle fibres in muscle cells require energy to contract
What is ATP?
Adenosine Triphosphate
A compound that transfers energy within cells
A RNA nucleotide that contains 3 phosphate groups
How does ATP release energy?
Energy is needed to break the bonds & is released when bonds are formed
A small amount of energy is needed to break the weak bond holding out the last phosphate group in ATP
A large amount of energy is released when this phosphate is involved with other reactions with bond formation
What is the equation for ATP releasing energy?
ATP + H20 -> ADP + Pi + Energy
What is the word equation for ATP releasing energy?
Adenosine Triphosphate + Water -> Adenosine Diphosphate + Inorganic Phosphate + 30.5kjmol-1
Why can ATP not be stored easily long term?
It is a relatively unstable molecule
How is energy stored in the body?
As fats & carbohydrates
How is ATP made during cellular respiration?
Fats & carbohydrates are broken down to release ATP
What are the properties of ATP?
Small -> can easily move in & out of cells
Water soluble -> energy requiring reactions can happen in aqueous environments
Contains a bond between phosphates with intermediate energy -> large enough to be used in cellular reactions, not large enough to be wasted as heat
Easily regenerated -> can be recharged with energy
What is DNA?
Deoxyribonucleic acid -> a double-stranded polynucleotide which carries the information for protein synthesis (contains the pentose sugar deoxyribose)
How does DNA form?
Nucleotides are joined in condensation reactions to form a polynucleotide chain. This happens as the phosphate group of one joins to the sugar molecule of the next which makes the sugar-phosphate backbone of the DNA molecule. This creates a single chain of DNA with the bases projecting out of the chain.
What is the structure of DNA?
The nucleic acid forms when the 2 polypeptide chains join together by hydrogen bonds between the nitrogenous bases, to form a double stranded molecule.
What is complementary base pairing?
Adenine & Guanine (purines) always pair up with Thymine & Cytosine (pyrimidines) as this is the only way the hydrogen bonds can form between the bases in DNA
How many hydrogen bonds does adenine form with thymine in DNA?
2
How many hydrogen bonds does guanine form with cytosine in DNA?
3
Why is complementary base pairing important?
So the molecule is stable and consistent in width
Do both DNA strands run parallel or antiparallel?
Anti-parallel
Are bases on nucleotides hydrophobic or hydrophillic?
Hydrophobic
How are polynucleotides synthesised?
Formation of phosphodiester bonds between nucleotides
Why does DNA need to replicate?
Each new cell has the full amount of DNA before cell division
Making new cells for growth & repair
Reproduction
Must form 2 sister chromatids so it has to be accurate
What is DNA replication controlled by?
Enzymes
What is Helicase?
An enzyme that catalyses the breaking of hydrogen bonds between the nitrogenous pairs of bases in a DNA molecule
When helicase breaks a DNA molecule, what are the products?
2 single strands of DNA with exposed nucleotide bases
What is DNA polymerase?
An enzyme that catalyses the formation of DNA from activated deoxyribose nucleotides using single stranded DNA as a template & forms phosphodiester bonds between the nucleotides
Which direction do the nucleotide bases add?
5’ to 3’
What is the function of DNA ligase?
Joins together short sections of the lagging strand
What is the function of the single strand binding protein?
Keeps the separated DNA strands apart during replication
How does DNA replicate?
DNA helicase causes hydrogen bonds to break which separates the 2 strands & DNA unwinds. Free nucleotides then join to the complementary unpaired bases. Hydrogen bonds then reform between the bases & DNA polymerase catalyses the formation of phosphodiester bonds between the nucleotides
What is semi-conservative DNA replication?
Half the DNA molecule is old DNA & half is made of new DNA
Is the plasmid DNA in prokaryotes semi-conservatively replicated?
Yes
How does DNA undergo continuous replication?
DNA polymerase always moves along the template strand in the same direction & can only bind to the 3 prime end so travels in the 3 to 5 prime direction. DNA polymerase has to replicate each of the template strands in opposite directions. the strand that is unzipped from the 3 prime end is continuously replicated & is the leading strand that undergoes continuous replication.
How does DNA undergo discontinuous replication?
The other strand is unzipped from the 5 prime end so DNA polymerase has to wait until a section of the strand has been unzipped & then work back along. This results in DNA being produced in okazaki fragments which then have to be joined. This strand is the lagging strand & undergoes discontinuous replication
Describe the stages of DNA replication?
1) DNA twists by the action of DNA helicase
2) Hydrogen bonds between base pairs break
3) Both strands act as a template
4) Free nucleotides align to the DNA & complementary base pair
5) Hydrogen bonds reform between the base pairs
6) The sugar-phosphate backbone forms, joining by a phosphodiester bond
7) This is catalysed by DNA polymerase
8) Two new DNA molecules form, semi-conservatively replicated
Why is is important that DNA is accurately replicated?
To make sure that genetic information is conserved each time DNA in a cell is replicated
What is a mutation?
A change to the DNA base sequence which may affect the phenotype of the organism
What is a transition mutation?
A type of substitution mutation where 1 pyrimidine is swapped for a different pyrimidine/1 purine swapped for a different purine
What is a transversion mutation?
Where a pyrimidine is swapped for a purine/ a purine swapped for a pyrimidine
Is a transition mutation more or less common than a transversion mutation?
More common
What are the 3 different types of substitution mutation where it occurs in a region of the gene that is involved in coding?
Silent
Missense
Nonsense
What is a Silent mutation?
The triplet codes for the same amino acid
What is a Missense mutation?
The triplet codes for a different amino acid (if it’s chemically similar it may have no noticeable effect -> neutral mutation)
What is a Nonsense mutation?
The triplet codon codes for a stop codon
What are frameshift mutations?
Mutations that alter the ‘reading frame’ of the gene downstream of the mutation which affects the structure of the protein
What are 2 examples of frameshift mutations?
Insertion & deletion mutations
