Moduie 9 - Genome Flashcards
What is a genome?
The genetic information belonging to a cell or an organism in a chromosome set
What types of DNA sequences are present and what are their relative proportions?
- Transposons: 43%
- Repeated Sequence: 50%
- Unique Sequence: 50%
- Genes: 23%
What is a gene and explain its directionality.
Gene is a region of DNA that is transcribed as a single unit and carries information for a discrete hereditary characteristics. For each DNA strand it has a 5’UTR (untranslated) and 3’UTR end, with a phosphate group in the 5’ end and hydroxyl group in the 3’ end.
What are pseudogenes?
Pseudogenes are copies of gene that are no longer functional. The copies may arise due to gene duplication event. The new gene would become obsolete and can undergo changes and mutation without selection.
Differ between tandem repeats & interspersed repeats.
- Tandem repeats: repeated end-to-end copies of short DNA sequence
- Interspersed repeats: they differ from tandem repeat DNA in that rather than the repeat sequences coming right after one another, they are dispersed throughout the genome and nonadjacent.
Differentiate between microsatellites and mini-satellites.
- Microsatellites: tandem repeats of very short (1-6 bp) DNA sequence for 10-150 bp
- Minisatellites: tandem repeats for short (7-100 bp) DNA sequence for 100-20000 bp
What are transposons and what is their importance in human health?
Transposons are parasitic genetic elements that can move about the genome. If it affects a functional gene (ie. move into it) it can affect’s the gene expression.
What is the difference between conservative & replicative transposition?
What are SINEs, LINEs and LTR retrotransposons?
Retrotransposons:
- Does not have transposase, but rather reverse transcriptase
- Target Site Duplication
- There are three main types:
- SINE: no rvt, short interspersed elements
- LINE: rvt, long interspersed element
- LTR retrotransposons: rvt, long interspersed elements, and long terminal repeats (LTR)
How do DNA transposons and retrotransposons differ in their structure?
DNA Transposons:
- Target Site Duplication: genomic sequence duplicat4ed during insertion
- Inverted terminal repeat: palindromic sequence involved in movement
- Transposase: enzyme involved in movement of DNA transposons
Retrotransposons:
- Does not have transposase, but rather reverse transcriptase
- Target Site Duplication
- There are three main types:
- SINE: no rvt, short interspersed elements
- LINE: rvt, long interspersed element
- LTR retrotransposons: rvt, long interspersed elements, and long terminal repeats (LTR)
Explain how gene density vary between species.
There is positive correlation between the complexity of the species with its genomic size. A larger genome doesn’t always equate to more genes as gene density varies between species. Species with a larger genome may have more intergenetic, repetitive DNA compared to those with a smaller one.
What are coding strand and template strand.
Template strand:
- serves as a template for transcription
- called the antisense strand
- strand runs in a 3’ to 5’ direction.
Coding Strand:
- it corresponds to the same sequence as the mRNA that will contain the codon sequences necessary to build proteins
- called the sense strand
- strand runs in a 5’ to 3’ direction.
What are exons and introns?
Exons (expressed sequences): are the parts of a gene that are present in the final, mature RNA form
Introns (intervening sequences): the parts of a gene that are removed by splicing
Differentiate between processed and unprocessed pseudogenes.
Processed pseudogene means the duplicated gene has its introns removed. That is achieved by first the process of transcription (removed intron, polyadenylation, 5’ capping) to make the corresponding mRNA before using reverse transcriptase to make DNA copy of the mRNA. The DNA is then inserted elsewhere in the genome.
In the case of unprocessed psedogene, it arises only due to a gene duplication event and the introns are intact.
How does gene fragments arise in chromosomes in the context of pseudogenes?
Non-functional genes (pseudogenes) can be broken up by chromosomal arrangements and remains due to not being selected against because there is a functional copy already present.
Describe the general structure of DNA transposons.
Transposase: an enzyme involved in movement of a DNA transposon
- Inverted terminal repeat (ITR): palindromic sequence involved in movement
- Target site dupliation (TDR): genomic sequence dupicated during insertion
