Flashcards in MCB Lecture 18 Intro to genes Deck (31)
What is the major functional division of the genome?
What are the two categories in unique sequences?
What is a gene?
A gene is a sequence of DNA that codes for a protein or a functional RNA
Differentiate between the coding and the template strand
Coding strand is identical to the mRNA
Template strand is the one read by the RNApol and is thus complimentary to the mRNA
What are related sequences?
UTRs, introns, exons
What are introns, exons and UTRs?
Introns: Intervening sequences. These interrupt the gene, are spliced out after transcription to form the mature mRNA
Exons: Expressed sequences. The parts that make up the mature mRNA
UTRs: regions between the 5' cap and the start of the gene and the end of the gene and the poly-A tail that are not translated
What is the average number of introns in a gene?
What are gene fragments?
This is when a part of the gene is separated from the rest and is no longer functional
What are pseudo genes?
What are the two types? Differentiate between the two
Pseudo genes look like genes, but have changed to become non-functional
Processed: mRNA has been reverse transcribed back into the genome. The introns are thus missing
Conventional: accumulation of mutation
What is example of a pseudo gene?
Beta globin genes
What are the two categories in 'intergenic sequences'?
What are the four categories in 'interspersed intergenic sequences?
What are retrotransposons?
How do these move around the genome?
These are transcribed from the gene to give mRNA.
Then, reverse transcriptase transcribes them back into DNA, and they insert in some other place in the genome
What are DNA transposons?
What are the two mechanisms for moving around the genome?
DNA transposons do not go through a mRNA intermediate: they are inserted directly into some other region of the genome.
Conserved: transposase enzymes bind at the ends of the gene, cleaves the phosphodiester bonds, and forms a loop. It then inserts it somewhere else
Replicative: sequence is copied directly into DNA and the copy inserts somewhere else
What are SINEs?
Short interspersed repeats
What are LINEs?
Long interspersed repeats
What are micro satellites?
How many base pairs per repeat?
Micro satellites are an array of short tandem repeats
Each repeat is 2-6 base pairs
What are mini satellites?
How many base pairs per repeat?
Mini satellites are an array of long tandem repeats
Each repeat is 10-60 bp
What are telomeres?
These are repeated regions at the end of a chromosome that prevent important regions from being cut off when during DNA replication
What are centromeres?
These are repeated regions whose function is to form the structure of the centromere
Describe the packing of chromosomes
Nucleosomes, coiling and super coiling to form chromosomes
Talk about variation in size of genomes
Different species have different sized genomes.
Smaller the organism, smaller the genome generally, but does not always hold. Eg. Locusts
Talk about gene density
This is number of genes per amount of DNA
Humans have very low gene density
What are LTRs?
Long terminal repeats
These are a type of interspersed repeat
What is a tandem repeat?
End to end repetition of DNA sequence at a defined locus
What are STRs and SSRs?
Short tandem repeats and Simple sequence repeats.
These are just other names for micro satellites
Which sort of repeat is much used for DNA profiling/fingerprinting?
What are replication origins?
Important, but non coding element in the DNA where replication begins
Half of the molecular mass of eukaryotic chromosomes is ...
Protein; the histones.
Describe the structure of histones
Core octamer of:
2 x H2A
2 x H2B
2 x H3
2 x H4