Genome Structure Flashcards
What is the genome
The entire genetic contents of an organisms
The genome of an organims can be
- Single Stranded DNA/RNA (bacterial viruses)
- Double Stranded DNA/RNA (most organisms will have this)
- Linear or Circular (most bacteria have circular DNA)
- Contained in single or multiple units
The bacteria E.coil has a Haploid size of 4.1Mbp
The simple single celled eukaryote (like Saccaromyces cervisiae - yeast) is how many times bigger
only 3 times bigger
There is not a big difference in the number of genes between some eukaryotes
The difference in sophisticated organisms (liked humans) and a little nematode worm is …
the control of the gene
Not the number or type of genes
What is the Chromosome
The physical location of the genes
Unlike prokaryotes (nucleoid) the genomes of eukaryotic cells can be found in several compartments
What are they
Nucleus
Mitocondria
Chloroplast
This is a picture of e.coil
What is the white arrow pointing to
The nucleoid
E.coil have one chromosome
Yeast has 32
What does this show
Genomes of organisms vary widely in chromosome number
Why are genes arranged in chromosomes?
Grouping together genes into chromosomes provides a convenient parcel of DNA that can be duplicated during DNA replication and partitioned into the daughter cells at cell division
(Down to natural selection)
What to chromosomes contain which allows them to be replicated
Chromosomes contain at least one origin of replication (ori), per chromosome
For some really long chromosomes you can have multiple points of origins or replication
Why do we have multiple chromosomes, rather than just one long one
If you had only one very long chromosome, the level of condensation found in normal chromosomes would not be sufficient in order to segregate into the two halfs of the cell (as shown in a normal cell below)
How can chromosome structures differ
The structures may be incredibly complex and ranges from pure nucleic acids (like in virsuses)
How many bases are there usually in a gene
1000 Bp to a gene
How many bases are there usually in a gene
1000 Bp to a gene
The DNA in bacteria chromosomes is folded
How
DNA is negatively charged
There is a set of proteins similar to hisotones, which are positively charged
The positively charged protein bind and wrap the DNA - sort of a loose arragment which is constantly associating and dissociating (fluid)
The DNA is also supercoiled - this supercoiling does not affect these loops which are formed however
What is the molecular material of a chromosome
- Ranges from pure nucleic acids as in Viruses
- Through a DNA/protein complex as in bacteria
- DNA in the chromosomes of eukaryotic cells is even more highly compacted being complexed with many different types of proteins at several levels to form ‘chromatin’
How do histones work in eukaryotic DNA?
147 base pairs of DNA wound around auto matic nucleosome core, with a short linker region, which is formed from chromatin
Apart from when DNA is being replicated, DNA is sequestered within these structures
Where is the promoter found on bacterial DNA and what is its function
The promoter sequence is where DNA polymerase binds (this is the little arrow next to RNA polymerase)
They are very short non-coding regions between bacterial genes
The promoter has a start codon and the terminator site a stop codon to start and end translation
These regions are very short
Genes are often crowed together into these constructs called operons
What is it?
Something that controls the expression of genes
In bacteria, genes with link functions are strung together into these operons
Example: two genes both controlled by the same promoter. Immediately after the translation of gene one you will have another start codon, to translate gene two
There can also be translation coupling: where there is overlap between the start and stop codon, so it reduced time for ribosome to move from gene 1 to gene 2
Say in humans vs bacteria
How muc of the genome encodes proteins
High proportion of sequences in bacteria code for proteins (98%)
In contrast this is only about (2%) in humans
This non-coding sequences are able to exist in humans due to their large size, not such a need for compact DNA compared to bacteria
How can DNA-specific stains be used to work out the amount of DNA
By working out the wavelength of light being emitted from a nucleus, this can be compared against a standard of a known volume of DNA
How does gene density vary along the chromosome
Very few genes at the ends telomere) or near the centromere
What does the typical trend of intron length look like
Across many species there are generally two typical sizes of introns (a smaller length and and a larger length)
What are exon/intron junctions
There is usually a GU at the start of an intro and a AG at the end of an intron
