Genetic info

Question 1

Structure of nucleotides

Answer 1

• 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

Question 2

Double-helical structure of DNA

Answer 2

• 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

Question 3

How is DNA compressed?

Answer 3

• 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

Question 4

Chromosomes

Answer 4

• Thread-like structures

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

Question 5

Chromatin

Answer 5

• 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

Question 6

How DNA strands are unzipped for replication

Answer 6

• 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

Question 7

2 major mechanisms chromatin is made more accessible

Answer 7

• Histones can be enzymatically modified

- Histones can be displaced by chromatin remodelling complexes

Question 8

How DNA is replicated

Answer 8

• 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

Question 9

How is DNA transcribed to RNA?

Answer 9

• 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

Question 10

Redundancy in amino acids

Answer 10

• 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

Question 11

Post-transcriptional processing of RNA

Answer 11

• mRNA -> carries info for protein synth

- tRNA (transfer) and rRNA (ribosomal) help in translation

Question 12

Alternative splicing

Answer 12

• 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

Question 13

Translation mRNA

Answer 13

• 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