1 - Organisation of the Human Genome

Question 1

What are the two genomes of every nucleated human cell

Answer 1

Mitochondrial and nuclear

Question 2

What does the mitochondrial genome encode

Answer 2

• 2 ribosomal RNAs (rRNA)
• 22 transfer RNAs (tRNA)
• 13 polypeptides
  DO NOT HAVE INTRONS

Question 3

Retrotransposons

Answer 3

• Sequences related to retroviruses
• Many truncated retroviral sequences in the genome
• Pol gene produces a reverse transcriptase which allows DNA to be integrated into the genome
• Can’t move between cells

Question 4

what does LINE stand for

Answer 4

Long INterspersed repeat Element

Question 5

What are LINEs

Answer 5

• Long (6-8kb),repetitive DNA sequences dispersed throughout the genome
• Encode proteins which are required for their integration into the genome
• 3 distinct LINE families, LINE1, LINE2 and LINE3. Only LINE1 is still transpositionally active

Question 6

What dose SINE stand for

Answer 6

Short INterspersed repeat Element

Question 7

What are SINEs

Answer 7

• Shorter than LINEs. Often aren’t able to integrate themselves
• Use LINE proteins to integrate
• Only remaining active family are ALUs

Question 8

Can LINEs and SINEs shift around

Answer 8

Yes and can introduce variation when they shift

Question 9

Transposable elements

Answer 9

• About 50% of genomic DNA is transposable elements
• Can damage the host genome through insertional mutagenesis or unequal crossover

Question 10

Microsatellites

Answer 10

• Short sequences (1-15bp) repeated in tandem many times (2-50)
• Results in “low complexity” sequence (e.g. GCGCGCGCGCGCGC)
• Prone to expansion and contraction during replication due to polymerase “slippage”

Question 11

Non coding RNA genes

Answer 11

a functional RNA molecule that is transcribed from DNA but not translated into proteins

Question 12

What are the major non coding RNA classes

Answer 12

• tRNA
• rRNA
• Short Regulatory ncRNA
• lncRNA

Question 13

Pseudogenes

Answer 13

• Sequences related to coding or non-coding sequences that have mutated so that expression/function is lost (e.g framshift)
• Derived from genes by duplication or retrotransposition

Question 14

Different types of pseudogenes

Answer 14

• Gene fragments
• Whole genes
• Processed pseudogenes

Question 15

Coding genes

Answer 15

• Produce proteins which perform activities required by the cell (metabolism, transcription, translation, etc)
• Can be single or multiple copy
• Grouped into families based on sequence similarity
• Identified by comparing mRNAs with genomic sequences

Question 16

General structure of coding genes

Answer 16

• Promoter
• Introns and exons (coding)
• 5’ UTR (drives translation)
• Start codon (ATG)
• Splice sites
• Splice enhancers (exonic, intronic)
• Stop codon (TAA, TAG, TGA)
• 3’UTR (mRNA stability & localisation)
• Polyadenylation signal (sequence)

Question 17

Human genome project results

Answer 17

• 50k-100k genes were predicted in the genome
• HGP found 20k-25k
• Alternative splicing explains the difference (some genes can produce >10 different proteins)