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Flashcards in Genetic info Deck (13):

Structure of nucleotides

- Made up of chain of nucleotide monomers (roughly 3 billion base pairs in length)
- Base: G, C, A or T
- Phosphate
- Deoxyribose sugar
- 2 strings of DNA in a twisted ladder


Double-helical structure of DNA

- Major groove and minor groove, very important for the strand itself, the major groove has many binding sites
- 10 bases for every full turn of the helix
- Anti-parallel, one runs 5' to 3' and the other vice versa, only way strand remains stable
- R handed spiral


How is DNA compressed?

- You coil up the structures into thread-like structures called chromosomes, there are 46 chromosomes in the body
- DNA is wrapped around 8 balls of histone proteins



- Thread-like structures
- Single piece of DNA containing many genes, regulatory elements and other nucleotide sequences



- Mixture of DNA, proteins and RNA that package DNA within the nucleus
- Divided between heterochromatin (condensensed, not used, can be junk) and euchromatin (extended) forms


How DNA strands are unzipped for replication

- Requires 2 strangs of DNA to separate temporarily to allow enzymes access to DNA template
- During interphase chromatin structure is optimised to allow easy access of transcription and DNA repair factors while compacting the DNA into the nucleus
- Cells either have to open up chromatin fibres and/or remove histones


2 major mechanisms chromatin is made more accessible

- Histones can be enzymatically modified
- Histones can be displaced by chromatin remodelling complexes


How DNA is replicated

- It is semi-conservative & bi-directional
- Special proteins 'unzip' the double helix by breaking the hydrogen bonds
- New nucleotide molecules are then paired with 2 DNA strands
- DNA polymerase can only add new nucleotides to the 3' end of the growing strand
- Okazaki fragments are formed on the lagging strand
- Joined together DNA ligase
- Telomerase replicates at 5' ends


How is DNA transcribed to RNA?

- There are exons (coding) and introns
- mRNA made: Transcription, elimination of introns and splicing of exons
- 3 bases are a codon, each codon specifies an amino acid
- 20 aminos in protein


Redundancy in amino acids

- Multiple codons code for the same amino acid
- You run into trouble if the first two bases are changed, the last amino acid can be changed -> wobble position


Post-transcriptional processing of RNA

- mRNA -> carries info for protein synth
- tRNA (transfer) and rRNA (ribosomal) help in translation


Alternative splicing

- Exons can be connected in multiple different ways during RNA splicing that leads to different protein isoforms
- Initiation codon determines the reading frame of the RNA sequence, until the termination codon, so it needs to be correct


Translation mRNA

- tRNA translates mRNA sequence into an amino acid
- Acts an adapter moleculr between the coded amino acid and mRNA
- rRNA are transported to cytoplasm, they combine with proteins to form a ribosome