Cell biology theme 4 Flashcards
What is the genome ?
the total genetic information carried by a cell or an organism
How much of the human genome codes for proteins ?
2%
How long is the human genome ?
3.2 x 10^9
How long is the mitochondrial genome ?`
17,000 bp
How long is the bacterial genome ?
4.6 million bp
What can comparison of genome sequences tell us ?
there are exon sequences that are highly conserved
some intron sequences can be conserved - not known why
What is special about mammals and fish ?
they diverged millions of years ago
this would have obliterated similar sequences but there are conserved genes and pieces of regulatory sequences
why can’t genome sequencing predict the biology if an organism ?
we dont know which sequences are genes
What are open reading sequences ?
sequences that are over 100 codons that lack a stop codon
what is an example of a start codon ?
AUG
What are examples of stop codons ?
TAA TAG and TGA
How can you test whether a sequence is a gene ?
isolate the sequence
place into the bacterial plasmid
test if its functional
What are distinguishing features of genes ?
they have splice site sequences - at intron/exon boundaries
they have promoters
codon bias
what are pseudogenes ?
nucleotide sequences resemble genes but have a mutation that prevents their expression
How can we use mRNA to sequence genes ?
collect mRNA and then reverse transcribe into DNA
map this back to DNA to get info on extragenic sequences and introns
but this is hard as most mRNA is non coding
What is the significance of homologues ?
a homologue is an organism with a high degree of similarity
if we know the function of a protein in another organism we can infer that the organism has a similar sequence
What is an ortholog ?
genes in different species that have evolved from a common ancestral gene. Identification of orthologs is critical for reliable production of gene function.
Are genes evenly distributed or not ?
no they are not evenly distributed in the genome
what have mobile genetic elements done ?
transposons and retrotransposons have multiplied and replicated themselves adding new copies in differnet positions
What are unique sequences ?
gene regulatory sequences
RNA sequences
unknown sequences
What do non protein coding sequences code for ?
microRNA and long non coding RNAs
How does miRNA work ?
it controls gene expression
base pairing with specific mRNAs
reduces their stability and ability to translate into a protein. mRNA is destroyed into nucleases
What is the RNA induced silencing complex ?
Double stranded siRNAs are taken up to RISCs
one strand is discarded and the other is used to bind to target RNA
How do long non coding RNAs work ?
they coat the chromosome and attract enzymes in chromatin remodelling complexes this alters gene expression as highly condensed chromatin forms
What are regulatory DNA sequences ?
promoters
enhancers
transcriptional regulators
What are epigentic changes ?
changes in gene expression that do not involve changes in the DNA sequence