Nucleotides and Nucleic acid Flashcards
What are nucleic acids?
They are polymers that are made from the monomer, nucleotides
What are the types of nucleic acid?
DNA and RNA
What is DNA used for?
It is used to store genetic information
What is RNA used for?
It is used to make proteins from the instructions in DNA
What are nucleotides?
They are monomers that make up nucleic acids
What are the components that nucleotides are made up of?
Phosphate groups
Pentose sugar
Nitrogenous base
How is a polynucleotide formed?
It is formed when nucleotides are linked together in a condensation reaction.
The phosphate group on carbon 5 bonds with the OH on carbon 3 of a pentose sugar on another nucleotide and they form a phosphodiester bond
What is the hydrolysis reaction of a polynucleotide?
It is adding water molecules to break the phosphodiester bond forming individual nucleotides
What are the 2 groups of DNA bases?
Purine and
Pyrimidine bases
What are purine bases and what bases are purine bases?
Purine bases are large bases that have 2 carbon rings. Adenine and guanine are purine bases
What are pyrimidine bases and what bases are pyrimidine bases?
Pyrimidine bases are smaller bases that have one carbon ring. Thymine, Cytosine and uracil are pyrimidine bases.
Describe the structure of DNA
It consists of two polynucleotide chains that are antiparallel. The polynucleotide chains are made up of a sugar-phosphate backbone and complementary bases in the center which are held together by hydrogen bonds
Explain the base pairing rule (3 marks)
A purine base will always pair with a pyrimidine base (1) Adenine will always form 2 hydrogen bonds with thymine(1) and guanine will always form 3 hydrogen bonds with cytosine(1)
What is the structure of RNA
It is a one polynucleotide strand that has a ribose sugar and has the bases adenine,uracil,guanine and cytosine
Stages of semiconservative DNA replication
- DNA helicase unwinds the DNA double helix separating the two polynucleotide strands and breaks the hydrogen bond between the bases
- Free activated nucleotides join to exposed bases by complementary base pairing.
- DNA polymerase catalyses the formation of phosphodiester bonds between the free activated nucleotides forming the sugar-phosphate backbone of the new DNA strand
- DNA ligase joins the fragments
Explain how the structure of DNA is ideally suited to its role. (4 marks)
Polymer so contains lots of information (1), idea that base sequence is used as codes(1), double stranded so molecule is stable (1), double stranded so accurate replication (1)
Explain why DNA replication is described as semiconservative (4 marks)
When DNA replicates, the double helix unwinds into two separate strands (1) Free nucleotides pair with complementary bases (1) Two new molecules of DNA are produced (1), each with one old strand and one new strand (1)
What is a gene?
It is a short section of the DNA that contains the base sequence that codes for an entire protein
What is transcription?
It is a process that converts DNA into mRNA
Why does transcription occur?
It occurs because the DNA is too large to leave the nucleus so the genetic information is copied in the form of mRNA
Describe the process of transcription
- The DNA unwinds and DNA helicase breaks the hydrogen bonds between the bases of the two strands
- Complementary free RNA nucleotides join up with the exposed bases on the antisense strand and are held by hydrogen bonds
- RNA polymerase synthesises the formation of phosphodiester bonds between the RNA nucleotides
- RNA polymerase detaches from the DNA strand and leaves allowing the DNA strands to join back together to go back to its double helix structure
- the mRNA formed then leave the nucleus and goes to the cytoplasm where it is translated
What is the mRNA strand complementary to?
The mRNA strand is complementary to the template strand of the DNA (runs in the 3’ to 5’ direction)
What is the mRNA the same as?
The mRNA is the same as the sense strand (runs the right way up which is the 5’ to 3’ direction) except thymine has been replaced with uracil
What is the template strand?
It is the strand which the base sequence is complementary to, to form mRNA
