Nucleic acids Flashcards
What is the structure of a nucleotide?
A phosphate group, pentose sugar and nitrogen containing base
Name the pentose sugars in DNA and RNA
DNA: deoxyribose
RNA: ribose
State the role of DNA in living cells
Base sequence of genes codes for functional RNA and amino acid sequence of polypeptides
Genetic information determines inherited characteristics
State the role of RNA in living cells
mRNA: Complementary sequence to 1 gene from DNA with introns spliced out. Codons can be translated into a polypeptide by ribosomes
rRNA: Component of ribosomes
tRNA: Supplies complementary amino acids to mRNA codons during translation
How do polynucleotides form?
Condensation reactions between nucleotides form strong phosphodiester bonds
Describe the structure of DNA
Double helix of 2 polynucleotide strands
H-bonds between complementary base pairs on opposite strands:
A + T
G + C
Which bases are purine and which are pyrimidine?
A and G = 2 ring purine bases
T and C and U = 1 rings pyrimidine bases
Name the complementary base pairs in DNA
2 H bonds between A and T
3 H bonds between G and C
Name the complementary bases in RNA
2 H bonds between A and U
3 H bonds between G and C
Relate the structure of DNA to its functions
Sugar phosphate backbone and many H bonds provide stability
Long molecule stores lots of information
Helix is compact for storage in nucleus
Base sequence of triplets codes for amino acids
Double stranded for semi-conservative replication
Complementary base pairing for accurate replication
Weak H bonds break so strands separate for replication
Describe the structure of mRNA
Long ribose polynucleotide
Contains uracil instead of thymine
Single stranded and linear
Codon sequence is complementary to exons of 1 gene from 1 DNA strand
How is mRNA suited to its functions?
Breaks down quickly so no excess polypeptide forms
Ribosome can move along strand and tRNA can bind to exposed bases
Can be translated into a specific polypeptide by ribosomes
Describe the structure of tRNA
Single strand of about 80 nucleotides
Folded into a clover shape
Anticodon on one end, amino acid binding site on the other
Anticodon binds to complementary mRNA codon
Amino acid corresponds to anticodon
Order DNA, mRNA and tRNA according to increasing length
tRNA
mRNA
DNA
Why is DNA replication described as semiconservative?
Strands from one original DNA molecule act as a template molecule
New DNA molecule contains 1 old strand and 1 new strand
Outline the process of semiconservative DNA replication
- DNA helicase breaks H bonds between base pairs
- Each strand acts as a template
- Free nucleotides from nuclear sap attach to exposed bases by complementary base paring
- DNA polymerase catalyses condensation reactions that join adjacent nucleotides on new strand
- H-bonds reform
Describe the structure of ATP
Nucleotide with an adenine with 3 phosphate groups
Explain the role of ATP in cells
Energy released is coupled to metabolic reactions
Phosphate group phosphorylates compounds to make them more reactive
How is ATP resynthesised in cells?
ATP synthase catalyses condensation reaction between ADP + Pi
During photosynthesis and respiration
Why is water a polar molecule?
O is more electronegative than H so attracts the electron density in the covalent bond more strongly
State 4 biologically important properties of water
Metabolite / solvent for chemical reactions in the body
High specific heat capacity
High latent heat of vapourisation
Cohesion between molecules
Explain why water is significant to living organisms
Solvent for polar molecules during metabolic reactions
Enables organisms to avoid fluctuations in core temperature
Cohesion-tension of water molecules in transpiration stream
What are the inorganic ions and where are they found in the body?
Ions that do not contain carbon atoms
Found in cytoplasm and extracellular fluid
May be in high or very low concentrations
Explain the role of hydrogen ions in the body
High concentration of H+ = low pH
H+ ions interact with H bonds and ionic bonds in tertiary structure of proteins which can cause them to denature
Explain the role of iron ions in the body
Forms Haem groups
Haem group has binding site to transport 1 molecule of O2 around body in the bloodstream
4 Haem groups per haemoglobin molecule
Explain the role of sodium ions in the body
Involved in co transport for absorption of glucose and amino acids in the lumen of the gut
Involved in propagation of action potentials
Explain the role of phosphate ions in the body
DNA
ATP
NADP
cAMP
