2.1.3 Nucleic acids Flashcards
Name the pentose sugars in DNA and RNA
DNA: deoxyribose
RNA: ribose
Describe how polynucleotide strands are formed and broken down
- Condensation reactions between nucleotides form strong phosphodiester bonds
- Hydrolysis reactions use a molecule of water to break these bonds
- Enzymes catalyse there reactions
Describe the structure of DNA
- Molecule twists to form double helix of 2 deoxyribose polynucleotide strands (so there are 2 sugar phosphate backbones)
- Hydrogen bonds form between complementary base pairs on strands that run antiparallel
Name the purine bases and describe their structure
- Adenine C5H5N5
- Guanine C5H5N5O
- (2 ring molecules)
Name the pyrimidine bases and describe their structure
- Thymine C5H6N2O2
- Cytosine C4H5N3O
- Uracil C4H4N2O2
- (one ring molecules)
Why is DNA replication semiconservative
- Strands from original DNA molecule act as templates
- New DNA molecule contains 1 old strand and 1 new strand
- Specific base pairing enables genetic material to be conserved accurately
Explain the role of DNA helicase in semiconservative replication
Breaks hydrogen bonds between base pairs to form 2 single strands which can acts as a template
How is a new strand formed during semiconservative replication
- Free nucleotides from nuclear sap attach to exposed bases by complementary base pairing
- DNA polymerase joins adjacent nucleotides on new strand in 5’ -> 3’ direction via condensation reaction to form phosphodiester bonds
- Hydrogen bonds reform
Identify features of the genetic code
- Non overlapping: each triplet is only read once
- Degenerate: more than one triplet codes for the same amino acid
- Universal: same bases and sequences used by all species
How does a gene determine the sequence of amino acids in a protein
Consists of base triplets that code for a specific amino acid
Describe how DNA can be purified by precipitation
- Add ethanol and a salt to aqueous solution
- Nucleic acids precipitate out of solution
- Centrifuge to obtain pellet of nucleic acid
- Wash pellet with ethanol and centrifuge again
What does transcription produce and where does it occur
- Produces mRNA
- Occurs in nucleus
Outline the process of transcription
- RNA polymerase binds to promoter region on a gene
- Selection of DNA uncoils into 2 strands with exposed bases. Antisense strands acts as template
- Free nucleotides are attracted to their complementary bases
- RNA polymerase joins adjacent nucleotides to form phosphodiester bonds
What happens after a strand of mRNA is transcribed?
- RNA polymerase detaches at terminator region
- Hydrogen bonds reform and DNA unwinds
- Splicing removes introns from pre mRNA in eukaryotic cells
- mRNA moves out of nucleus through nuclear pores and attaches to ribosome
What does translation produce and where does it occur
- Produces proteins
- Occurs in cytoplasm and on ribosomes (which are made of protein and rRNA)
Outline the process of translation
- Ribosomes move along mRNA until start codon
- tRNA anticodon attached to complementary bases on mRNA
- Condensation reactions between amino acids on tRNA form peptide bonds. Requires energy from ATP hydrolysis
- Process continues to form polypeptide chain until stop codon is reached
Describe the structure of adenosine triphosphate (ATP) and adenosine diphosphate (ADP)
- ATP has 3 organic phosphate groups
- ADP has 2
What is a mutation
- An alteration the DNA base sequence
- Mutations often arise spontaneously during DNA replication
