Biological molecules - Nucleotides and Nucleic acids Flashcards
are nucleic acids polymers
yes
what are the monomer units in nucleic acids
nucleotides
what are the subunits in nucleotides
- phosphate group
- pentose sugar
- nitrogenous base
how are the subunits in a nucleotide joined
by covalent bonds
how many nitrogenous bases are there for DNA
four
how are the nitrogenous bases for DNA grouped
two are purine (two rings) and two are pyrimidine (one ring)
what are the four bases in DNA and which are purine or pyrimidine
purine bases: adenine, guanine
pyrimidine bases: thymine, cytosine
how do the bases in DNA go together
A and T, C and G
what are phosphorylated nucleotides
contain more than one phosphate group
give two examples of phosphorylated nucleotides and explain their function
adenosine triphosphate (ATP) and adenosine diphosphate (ADP).
these molecules are the “energy currency” of cells. the hydrolysis of ATP to ADP + Pi releases energy
how is ATP made
respiration
describe the structure of ATP
three phosphates (attached to carbon 5 ), ribose, adenine
how many types of nucleic acids are there, and what are they
2
- deoxyribonucleic acid (DNA)
- ribonucleic acid (RNA)
what do nucleic acids do
they are molecules that hold the coded information required to build an organism and keep it running
is DNA a polymer
yes, the monomers are nucleotides
how is DNA formed
the nucleotides join up between the phosphate group on one nucleotide and the carbon 3 of the sugar of another via a condensation reaction. this forms a phosphodiester bond
describe the structure of DNA
- DNA consists of 2 polynucleotide strands
- the strands are made of a sugar-phosphate backbone attached to nitrogenous bases
- its shape is a twisted double helix
- the strands run in opposite directions (antiparallel)
- hydrogen bonds form between the bases - 2 bonds between A and T and 3 bonds between C and G
how many bonds form between the bases
2 bonds between A and T and 3 bonds between C and G
how do bases join
hydrogen bonds form between the bases on the two polynucleotides, this stabilises the structure
why is it important for the DNA molecule to be stable
it needs to be replicated
what are the rules for complementary base pairing
purine always paired with pyrimidine
A-T (2 hydrogen bonds)
C-G (3 hydrogen bonds)
what is the sugar in DNA
deoxyribose
explain how the structure of DNA is ideally suited to its role
- base sequence used as code
- polymer - lots of information
- double stranded - stable, accurate replication
- complementary base pairing allows it to be copied and transcribed
- hydrogen bonds can be broken/made so can be copied and read easily
describe DNA in eukaryotes
- the majority of DNA is found in the nucleus
- DNA is wound around histone proteins, making chromosomes
- there are also loops of DNA, without histones, inside mitochondria and chloroplasts
describe DNA in prokaryotes
- DNA is a loop within the cytoplasm (no nucleus)
- it is “naked” not wound around histone proteins
- small loops called plasmids often present
describe the general method for extracting DNA
- add detergent and salt (also maybe protease to denature histones) to a zip lock bag, then add the fruit and remove air
- mash
- filter
- transfer to boiling tube and pour chilled ethanol down the side
why must DNA be copied each time a cell divides
so that each new daughter cell has the full set of instructions
when does DNA replication take place
during interphase in the cell cycle before mitosis
describe chromosomes in eukaryotes after replication
each chromosome is composed of 2 chromatids held together at the centrosome
describe the products of DNA replication
2 DNA molecules identical to each other. each molecule contains one of the old strands and one new strand. this is why it is called semi-conservative replication
what kind of replication is DNA replication
semi-conservative
what is the first step of DNA replication
DNA untwists and unzips (the hydrogen bonds between the bases are hydrolysed). this is catalysed by DNA helicase
what is the second step of DNA replication
free nucleotides in the nucleoplasm bind at the exposed complementary bases
what is the third step of DNA replication
hydrolysis releases the extra phosphate groups from the nucleotides and supplies energy to form the phosphodiester bonds between the sugar of one nucleotide and the phosphate groups of the adjacent nucleotide.
this is catalysed by DNA polymerase
what direction does DNA polymerase work in
5’ to 3’ direction
what is the fourth step of DNA replication
the leading strand is synthesised continuously as DNA polymerase keeps working in the 5’ to 3’ direction as new bases are exposed
the lagging strand is synthesised in fragments (Okazaki fragments) joined using DNA ligase enzymes
