Nucleic acids + DNA replication Flashcards
DNA functions
- stores genetic information
- directs own replication
- directs transcription of complementary molecule of mRNA
mRNA functions
- carries genetic information
- directs translation of genetic information into proteins
- copied from DNA and used as template for protein synthesis
tRNA functions
- translator of genetic information
- deliver amino acids to ribosomes in protein synthesis
rRNA functions
- components of ribosomes
- structural + functional roles
- involved in binding mRNA and tRNA in protein synthesis
Purine bases
- adenine + guanine
- 2 rings
Pyrimidine bases
- cytosine + thymine + uracil
- 1 ring
Nucleoside
bases + 5-carbon (pentose) sugar
Nucleotide
phosphorylated nucleosides (5’ position of sugar)
Watson-Crick base pairing
- Adenine + thymine = 2 hydrogen bonds
- Guanine + cytosine = 3 hydrogen bonds
(guanine/cytosine rich regions more stable)
Anti-parallel
strands run in opposite directions
DNA primary structure
chains of nucleotides held together by phosphodiester bonds attaching the phosphates
DNA secondary structure
2 strands of DNA held together by hydrogen bonds between complementary bases
DNA tertiary structure
DNA wrapped around histones, forming chromatin
chromatin is then packaged into nucleosomes
then supercoiled into a chromosome
Describe process of transcription
- double-stranded DNA separated into coding + template strand
- template strand complementary to RNA transcript
- complementary nucleotides added by RNA polymerase to growing RNA molecule
- template strand read from 3’-5’
- RNA synthesised from 5’-3’
What are the different types of RNA polymerase?
generally, RNA polymerases synthesise RNA molecules
RNA polymerase 1 = directs synthesis of rRNA
RNA polymerase 2 = directs synthesis of mRNA
RNA polymerase 3 = directs synthesis of tRNA
mRNA structure (prokaryotic)
polycistronic (encode multiple proteins)
no chemical modifications
no splicing
mRNA structure (eukaryotic)
monocistronic (encode a single protein)
chemical modifications = 5’ methylated guanine nucleotide cap, 3’ = polyA tail
splicing (removal of introns + ligation of exons)
consists of introns and exons
tRNA structure
trinucleotide anticodon (on anticodon loop) = directs specific interaction with appropriate codon in mRNA variable loop acceptor stem = amino acid can join here clover leaf secondary structure
Describe the ribosomes and rRNAs in prokaryotic cells
70s ribosomes
large and small subunits
sizes = 50s +30s
rRNA = 23s, 5s, 16s
Describe the ribosomes and rRNAs in eukaryotic cells
80s ribosomes
large and small subunits
sizes = 60s + 40s
rRNA = 28s, 5.8s, 5s, 18s
Which antibiotics are ribosome-inhibiting and what ribosomes do they target?
streptomycin = 30s subunit erythromycin = 50s subunit tetracycline = 30s subunit chloramphenicol = 50s subunit
What is the type of DNA replication?
semi-conservative
2 parental DNA strands act as template for new DNA and after replication each double-stranded DNA contains one strand from the parental DNA and one new (daughter) strand
Which experiment proved the semi-conservative method of DNA replication?
Meselson and Stahl
used E.Coli DNA made with 2 nitrogen isotopes (14 +15)
and density gradient centrifugation
Describe DNA replication in eukaryotes
initiation = proteins bind to origin of replication and helicase unwinds DNA helix - 2 replication forks formed at origin of replication
elongation = primer sequence added with complementary RNA nucleotides which are then replaced with DNA nucleotides
during elongation, leading strand is made continuously, lagging strand made in pieces (Okazaki fragments)
termination = primers removed and replaced with new DNA nucleotides and backbone sealed by DNA ligase
