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In prokaryotes, the genome is usually contained in a single, circular DNA molecule, localized within the __
- nucleoid (no real nucleus)
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Chromosomes of most prokaryotes are __
circular and single (chromosome is haploid)
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plasmids
- small, circular, DNA molecules that are found inside some prokaryotic cells in multiple copies
- considered as independent entities from bacterial genome and are not part of bacterial genome
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Plasmids are important for __
antibiotic resistance or virulence genes
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Bacterial genomes have __ genetic organizations & only __ of E. coli genome is noncoding DNA. A very small part of E. coli genome is the __
- compact (very little space between genes);
- 11%;
- origin of replication (the start point of DNA polymerization)
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Chromosomes of eukaryotes are __
- linear and multiple (variable numbers from organism to organism)
- usually diploid, but at some stages of life can be haploid (gametes), sometimes polyploid
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The genome of eukaryotes is enclosed in __
a nucleus
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DNA is packaged with __ into a structure known as a chromosome
proteins
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importance of chromosomes
- Packaging of DNA is very important as it is a very long and narrow molecule. (DNA is compacted and packaged into the chromosome).
- DNA is more protected and stable in the chromosome.
- Only packaged DNA can be reliably transmitted to the daughter cells during cell division.
- DNA is organized in the chromosome and its accessibility and expression of its info is regulated within the chromosome.
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In the nucleus of eukaryotic cells that are not dividing, __ is the DNA with its associated proteins.
chromatin
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The most abundant proteins associated with DNA are __ that are small basic proteins.
histones
DNA is wrapped around histone octamers.
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__ proteins (less common) include DNA interacting proteins involved in DNA repair, replication, recombination, transcription, etc.
Non-histone
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In eukaryotes, the __ is more correlated with the complexity of the organism, not the __
- number of genes;
- size of the genome
- The size of genome is very variable between different organisms.
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Genes are more __ in prokaryotes than eukaryotes. Roughly, there is a __ between the density of genes and the complexity of the organism.
dense; reverse correlation
Viruses have the highest gene density, followed by bacteria. In eukaryotes, large sequences of DNA allocated for the regulation of gene expression.
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Proteins coded by eukaryotes on average have __ sizes to prokaryote proteins
similar
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The reasons for increase in the size of eukaryotic genomes are:
- increase in the size of intergenic sequences
- interrupting sequences within the gene (introns)
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In humans, 95% of the size of the gene is from __ and 5% is from __
introns; coding sequences
(More complex organisms have more and longer introns.)
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Humans have a __ % of repetitive DNA and has __ gene density. Fungi has a __ % of repetitive DNA but has __ gene density.
- large; low
- small; large
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intergenic sequences
- does not code for structural or functional proteins or functional RNAs
- make up 60% of the genome of humans (The other 40% are genes and gene related sequences.)
- 2 types: unique and repeated
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regulatory sequences
- the areas of the genome that contribute in regulating expression of genes
- also part of non-coding regions of DNA
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It has been discovered that intergenic sequences also contain __
- the genes for regulatory RNA molecules such as long intervening non-coding RNA (lincRNA)
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Sequences that are associated with the gene, such as introns and untranslated regions are __ than the coding areas.
- much larger
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Approximately 62% of the human genome comprises of __, which have no known function. These sequences used to be called junk DNA (but in fact they may have important functions)
intergenic regions (between genes)
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The bulk of intergenic DNA is made up of __ (half of human genome)
repeated sequences
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individual repeat units distributed around the genome
- interspersed repeats (genome wide repeats)
- 45% of genome
- (longer than tandem repeats)
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repeat units that are placed next to each other in an array
tandemly repeated DNA
- (Some of these tandem repeats are in the centromere and telomere - may have structural function - and also in other parts of the genome.)
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repeats of 6-10 nucleotides. e.g. telomeric DNA, which in humans comprises hundreds of copies of the motif 5'-TTAGGG-3'
mini satellites
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the repeat unit is short - from 1 to 5 bp in length - The most common type is dinucleotide repeats and single nucleotide repeats (e.g. AAAAA)
microsatellites
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nonfunctional gene copies
pseudogenes
- (accumulate more and more mutations during evolution)
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conventional pseudogene
a gene that has been inactivated because its nucleotide was changed by mutation
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processed pseudogene
- looks like a CDNA copy of an mRNA which reinserted into the genome
- doesn't contain any introns and lacks 5'
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Chromosomes need a __ to be maintained during cell divisions
- centromere, telomere, and origin of replication
- (These are neither genes nor regulatory sequences.)
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origin of replication
- the site at which DNA replication machinery assembles and replication is started
- One in very 30 - 40kb in eukaryotic chromosome, in the non-coding region of the chromosome
- There is one origin of replication in prokaryotes in their single chromosome.
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metaphase chromosomes: For the purpose of cell division, the DNA adopts a more __ form of packaging.
compact
(resulting in the highly condensed form that can be seen with the light microscope)
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The metaphase chromosomes form after __ has taken place, and so each contains __ copies held together at the __
- DNA replication;
- 2;
- centromere
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The arms of the chromosomes are called __ and have terminal structures called __
- chromatids (2 sister chromatids); telomeres
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In the majority of eukaryotes, the centromere is __ and is made up of __
large; repetitive sequences
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kinetochore
The structure (contains > 20 proteins) binds to the centromere and acts as the attachment point for the microtubules (spindles) which pull the divided chromosomes into the daughter nuclei
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