Genome Structure Flashcards
describe eukaryotic nuclear genomes
typically large, linear, and made of many separate chromosomes; large intergenic spaces and introns (only 1.5% of human genome is protein coding)
describe prokaryotic genomes
typically small (100,000 - 5 million bp), circular, often just a single chromosome; very compact, most of the genome encodes proteins, few intergenic spaces and no introns
why are prokaryotic genomes so small compared to ours?
vast majority of size difference is due to non-protein coding sequences (basically just promoters and protein coding sequences - no exons in bacteria)
why is gene regulation simpler in single-celled organisms versus multicellular organisms?
because they don’t have to make different types of cells
main reason for bacteria to regulate genes
to respond to their environment
what did chloroplasts and mitochondria evolve from?
symbiotic prokaryotes (bacteria)
mitochondria have their own ___. it looks similar to a _______.
genome; bacterial genome
describe our mitochondrial genome
circular, very tiny and compact, most genome encodes protein, few introns and intergenic sequences
mitochondrial genome bp in humans vs yeast, why is there a big difference?
17,000 bp in humans; 78,000 bp in yeast
eukaryotic cells provide a lot for the mitochondria (give food, break things down) so the mitochondria don’t need as much of the genome
describe the chloroplast genome
circular, not as small as mitochondrial genome, compact, few introns and intergenic regions
how many bp in a chloroplast genome?
100,000-200,000 bp
how many chloroplasts in a leaf cell?
100-10,000 chloroplasts
how many mitochondria are in an animal cell?
1,000-5,000 mitochondria
does yeast have a linear or circular genome?
eukaryote so linear
size (in bp) of human nuclear genome
3.2 billion bp
how many chromosomes do we have (haploid)?
23
size (in bp) of each chromosome
57-250 million bp
size (in protein coding genes) of each chromosome
200-2000 protein coding genes
total protein-coding genes combined (on all chromosomes)
20,000 protein coding genes
what percent of genome is translated?
1.5% translated (protein-coding)
what percentage of the human genome consists of repetitive elements?
60%
what do most of the repetitive sequences of DNA consist of?
transposable elements (transposons)
what are transposons?
“jumping genes” that can cut, or copy, and then past themselves into new locations in the genome
what kind of transposons encode proteins that allow them to jump?
autonomous transposons
what do retrotransposons contain that allow them to be transcribed?
have a promoter and get transcribed
autonomous retrotransposons are translated into?
2 proteins, one of which is a reverse transcriptase which creates a complementary DNA sequence that is then integrated into the genome
what does it mean for most retrotransposons to be inactive?
they are mutated so that they can’t be transcribed and/or translated; they are molecular fossils
what step allows one retrotransposon to become many?
the transcription step
what % of the human genome is retrotransposons?
41%
what percent of the human genome is DNA transposons?
3%
are DNA transposons transcribed?
transcribed and translated, but there is no reverse transcriptase
when can DNA transposons be duplicated?
if it “jumps” during DNA replication
short DNA sequences over and over again in tandem
tandem repeat sequences
what are tandem repeat sequences classified by?
size of repeated sequence
percent of human genome that is tandem repeat sequences?
3%
what are minisatellites?
group of tandem repeat sequences; 10-60 bp long repeated 5-50 times
what are microsatellites?
group of tandem repeat sequences; 1-9 bp long and highly variable between individuals in a species
what are microsatellites useful for?
DNA fingerprinting
how might mini or micro satellites be extended or shortened?
by basal slippage of DNA polymerase during replication
what kind of repetitive DNA sequences DO NOT need DNA polymerase to be duplicated?
a) DNA transposons
b) retrotransposons
c) microsatellites
d) minisatellites
b) retrotransposons
define polyploidy
having multiple copies of the whole genome
why do related plants and animals have very different genome sizes?
mostly due to polyploidy, also due to frequency of repetitive elements like retrotransposons
genome size DOES NOT correlate to the ____ of an organism
complexity
the cell doesn’t seem to care about the amount of DNA, rather _____
the number of genes
most multicellular organism have _____ of protein-coding genes; which is around _____
the same; 20,000
how many protein-coding genes do unicellular organisms have?
5000 protein-coding genes
