Storage and Replication of Genetic Information Flashcards
Why is RNA unstable?
The lone pair of electrons on the O in the OH group of the 2’ carbon of the sugar interacts with the phosphate
Which bases are purines?
- Adenine
- Guanine
Which bases are pyrimidines?
- Cytosine
- Thymine
What is satellite DNA?
Blocks of tandem repeats
What is a mini satellite?
Up to 1000 copies of the repeat in a block (not just 3 bases)
What is a micro satellite?
A smaller array of simple sequence repeats (eg. CAG)
Where are both types of satellite typically found?
- Mini = centromere and telomere
- Micro = non-coding DNA
What is the role of the telomeres?
Allow replication to tip of the chromosome
What is the role of the centromere?
Proteins involved in cell division bind to centromeric sequences
Types of chromatin
- Euchromatin
- Heterochromatin
What is euchromatin?
Less compact chromatin found in gene-rich areas to allow easy binding for transcription proteins
What is heterochromatin?
Highly condensed region of interphase chromosome that is generally gene-poor/transcriptionally inactive
To which end are new nucleotides added?
3’ end (so replication is in a 5’ to 3’ direction)
What do initiator proteins do?
Recognise replication origins and open up the double helix into a ‘bubble’
What are ‘forks’?
The Y-shaped ends either side of the ‘bubble’
Which direction does DNA polymerase move in?
5’ to 3’ of NEW strand
What must be present for DNA polymerase to work?
- Template
- RNA primer
What are Okazaki fragments?
Small fragments that are built in the opposite direction to the direction of fork movement due to the parental strand being in the 5’ to 3’ direction
How are Okazaki fragments added to the chain?
- RNA primer added up-stream from already-replicated DNA
- Okazaki fragment built back towards previous primer
- Old primer erased and replaced with DNA
- DNA ligase joins new Okazaki fragment to already-replicated chain
What is the strand simply made as one long chain in the 5’ to 3’ direction?
Leading strand
What is the strand made in the 3’ to 5’ direction using Okazaki fragments?
Lagging strand
What is depurination?
Where guanine is completely removed from the nucleotide
What is deamination?
NH2 of cytosine replaced O, creating uracil
What causes thymine dimers?
UV radiation
What is a thymine dimer?
C=C bonds opened up on adjacent thymines and C-C bonds join the previously separate bases
