DNA Replication
Why does DNA need to replicate?
growth and maintenance
What is the ultimate goal of transcription?
use DNA as a template to make mRNA so it can be translated
what are codons and what are the different types?
segments of mRNA molecules made of 3 nucleotides
- sense codons: code for amino acid (includes start codon AUG)
- stop codons
What is a mutation and what are they caused by?
- any permanent change to the DNA sequence
- caused by replication errors and environmental factors (like UV)
How does DNA replicate?
semiconservatively
What is central dogma?
DNA --> (transcription) --> RNA --> (translation) --> protein
Describe a ribosome.
Made of two parts (only come together during translation):
- Large subunit – has 3 sites where tRNA can bind
• A = “amino acid”
• P = “polypeptide”
• E = “exit"
- Small subunit – checks codon and anticodon pairing; if incorrect, tRNA is ejected
What is incorporation error rate?
probability that an incorrect base will be inserted into a new strand of DNA, resulting in mismatch
Draw out initiation of DNA replication and include all components.
should include:
- DNA helicase
- replication fork (2)
- RNA primer and primase
- ori (origin of replication)
Draw out initiation of transcription and include all components.
should include:
- RNA polymerase
- promoter
- transcription initiation site
- transcription factors
- coding strand
- template strand
Draw out the initiation of translation and include all components.
should include:
- tRNA and small ribosome subunit bind to mRNA
(together = initiation complex) at the start codon
- Large subunit joins, with tRNA in P site
Describe mismatch repair.
- After replication, a mismatch repair complex checks the new strands of DNA
- If mismatch is found, it cuts out a small section from the new half of the DNA
- DNA polymerase comes back to redo that section
- Ligase connects the repair to the rest of the strand
Draw out elongation of DNA replication and include all components.
should include:
- DNA polymerase and its directionality (3' and 5')
- leading strand (made continuously)
- lagging strand (discontinuous)
- RNA primer
- Okazaki fragments
- Ligase
Draw out elongation of transcription and include all components.
should include:
- RNA polymerase and its directionality (3' and 5')
- mRNA
Draw out elongation of translation and include all components.
should include:
- Polypeptide synthesized as ribosome
moves along mRNA from 5’ to 3’
- Large subunit breaking one bond (amino acid
to tRNA) and forming another (amino acid to amino acid on next tRNA)
- Catalyst of this reaction a ribozyme
(ribonucleic acid and enzyme)
What are ways mutations can affect phenotype?
- Silent mutation: The change in the DNA sequence doesn’t change the amino acid that section codes for
- Loss-of-function: Causes the function of that gene to be lost, because the resulting protein is not functional
anymore
- Gain-of-function: Creates a new/different function for the gene by creating a different version of the protein
- Conditional mutation: Affect the phenotype in some
environmental conditions, but not others
Draw out termination of DNA replication and include all components.
should include:
- full length leading strand
- gap at end of lagging strand (shorter than parental strand)
Draw out termination of transcription and mRNA processing and include all components.
- termination ending at termination site
- pre-mRNA
- introns and exons
- mRNA splicing: spliceosome made of snRNPs, consensus sequence, splice sites
- alteration of ends: 5' cap and poly A tail
Draw out termination of translation and include all components.
should include:
- Ribosome reaching stop codon in
the A site, no tRNAs can base pair with it
- Polypeptide chain released, the tRNA, mRNA, and
ribosome subunits all separate
What are the types of mutations?
point mutations: one changed pair of bases
- substitutions: A pair of bases get substituted for a different pair
- deletions: deletes single base pair
- insertions: inserts single base pair
chromosomal mutations:
- deletions: loss of a section of a chromosome
- duplications: repetition of a segment of a chromosome, so there is an extra copy of the genes in that segment
- inversions: segment of a chromosome gets flipped around in the original location
- translocations: transfer of a chromosome segment to a different chromosome