2.3 Nucleotides and Nucleic acids Flashcards
(20 cards)
Define nucleotide
A subunit of DNA/RNA consisting of a nitrogenous base, a phosphate molecule, and a sugar- thousands link to form a DNA/RNA molecule
What are the bases?
Adenine, Guanine, Cytosine, Thymine (Uracil instead of Thymine in RNA)
What are the differences in a DNA and RNA nucleotide?
DNA:
Pentose sugar is deoxyribose
Thymine is a base
A molecule is a 2 strands twisted into a double helix
RNA:
Pentose sugar is ribose
Uracil is a base
A molecule is a single strand
The difference between a ribose and deoxyribose sugar and why it matters
At carbon 2 ribose has a hydroxyl group (OH facing down) and deoxyribose only has an H at this place- makes RNA more susceptible to hydrolysis- this is why RNA is the transport molecule with a shorter lifespan and DNA the storage molecule
Purines
Type of base, larger molecule, double ring nitrogenous compound, purines in DNA/RNA are adenine and guanine
Always bonds to pyrimidines
Pyrimidines
Type of base, smaller molecule, single ring nitrogenous compound, pyrimidines in DNA/RNA are cytosine and thymine/uracil
Always bonds to purines
What bonds and reactions occur in a nucleotide? (Synthesis and breakdown)
Phosphate and sugar joined by ester bond, Base and sugar joined by glycosidic bond (both require condensation reaction to occur)
What bonds occur between nucleotides?(synthesis of them)
Strong covalent bonds called phosphodiester bonds (phosphate group and 2 ester bonds), occur between phosphate of one nucleotide and the pentose sugar of another, chain these bonds produce known as the sugar-phosphate backbone, broken by hydrolysis
Structure of ADP and ATP as phosphorylated nucleotides
ADP- adenosine diphosphate (adenine, ribose, 2 inorganic phosphates)
ATP- adenosine triphosphate (adenine, ribose, 3 inorganic phosphates)
Glycosidic between the base and sugar, phosphoanhydride bonds between phosphate groups, phosphodiester bonds between phosphate of one ATP molecule and the pentose sugar of another
Ribose/deoxyribose formulae
Ribose- C5 H10 O5
Deoxyribose- C5 H10 O4
Why do bases only bond to other specific bases?
G and C and A and T/U are said to be complimentary base pairs
DNA structure
Double helix, 2 polynucleotide strands held together by hydrogen bonds, 3 H bonds between G and C and 2 H bonds between A and T (formed by condensation reactions), 2 nucleotide strands wound round each other at approx. every 10 bases, phosphodiester bonds between carbon 3 of one sugar, the phosphate, and carbon 5 of the other, strands run in opposite directions so said to be anti-parallel
Why is it called semi-conservative replication?
In each new DNA molecule produced, one of the DNA strands is from the original DNA molecule being copied and the other has been newly created in the cell’s nucleus
What role does DNA helicase have?
This enzyme moves along DNA backbone and catalyses reactions that break H bonds between base pairs, unwinding/unzipping the double helix
What role does DNA polymerase have?
This enzyme catalyses the forming of phosphodiester bonds between free nucleotides in the nucleoplasm to the template DNA strand
Process of semi-conservative replication
Helicase moves along DNA backbone and unwinds it by breaking H bonds between bases (forms 2 single polynucleotide DNA strands), strands act as template for free nucleotides in nucleoplasm to attract via base pairing, polymerase forms phosphodiester bonds between nucleotides to form sugar phosphate backbone, original and new strand join via H bonding between bases
The importance in conserving genetic information in DNA replication
Retaining one original strand ensures genetic/hereditary material is conserved so genes can be copied exactly
How is the structure of DNA suited to its function?
Large and compact allows large amount of genetic info to be stored in a small space
Weak H bonds between bases allow for replication
Complimentary base pairing provides stability and allows rapid/accurate copying
The conservative theory
States that DNA splits to form a daughter strand that’s completely identical and another strand that is genetically different (not true as is an outdated theory!)
Mutations occur in DNA replication when:
An extra base is inserted
A base is left out
Bases are inserted in the strand in the wrong order/paired to a base not complimentary to it (e.g. A pairing to G
