Genetics summary – VU BMS 2020/2021
Simone Zweers
Reference: Brooker, Genetics: Analysis and prinicples, 7th edition
Chapter 10: Molecular structure of chromosomes and transposable elements
1
, Genetics summary – VU BMS 2020/2021
Simone Zweers
Reference: Brooker, Genetics: Analysis and prinicples, 7th edition
- Chromosomes = the structures within living ells that contain the genetic material
- Genome = the entire complement of genetic material in an organism or species
- Bacteria, genome is a single circular chromosome
- Eukaryotes, genetic material is found in different cellular compartments
- Human nuclear genome = 22 autosomes, X and (in males) Y chromosomes. Also a mitochondrial
genome
- Chromosomal sequences facilitate four important processes:
o Synthesis of RNA and cellular proteins
o Replication of chromosomes
o Proper segregation of chromosomes
o Compaction of chromosomes so that they fit within living cells
- Transposable elements (TEs) = short segments of DNA which are able to move to multiple sites
within chromosomes and accumulate in large numbers
10.1: Organization of functional sites along bacterial chromosomes
- General features of a bacterial chromosome
- Mostly circular, sometimes linear
- Single type of chromosome, but more
copies can be found within one bacterial
cell
- Few million base pairs
- Few thousand different genes
- Protein-encoding genes = majority of
bacterial DNA
- Intergenic regions = non-transcribed
regions of DNA located between adjacent
genes
- Bacterial chromosomes have one origin of replication = a sequence that is a few hundred base
pairs in length → initiation site for the assembly of several proteins required for DNA replication
- Repetitive sequences = found in multiple copies, interspersed within the intergenic regions
throughout the bacterial chromosome. May play a role in a variety of genetic processes, including
DNA folding, replication, regulation and genetic recombination
10.2: Structure of bacterial chromosomes
- Chromosome is highly compacted and found within a region of the cell = nucleoid
- Bacteria may have one to four identical chromosomes per cell, number of copies
vaires depending on the bacterial species
- Each chromosome is found in its own distinct nucleoid in the cell
- Bacterial nucleoid is not a separate compartment, the DNA in a nucleoid is in
direct contact with the cytoplasm of the cell
The formation of chromosomal loops helps make the bacterial chromosome more
compact
- To fit in the bacterial cell, chromosomal DNA must be compacted about 1000-fold
- Microdomains = loops that emanate from the core are 10.000 bp long. E.coli
chromosome has about 400-500 microdomains
- many microdomains are further organized into macrodomains, 800/1000 kbp
long, 1 macrodomain = 80/100 microdomains
- nucleoid-associated proteins (NAPs) needed for the forming of micro and
macrodomains → DNA-binding proteins, facilitate chromosome compaction and
organization
o they bend the DNA or act as bridges
o facilitate chromosome segregation
2
Simone Zweers
Reference: Brooker, Genetics: Analysis and prinicples, 7th edition
Chapter 10: Molecular structure of chromosomes and transposable elements
1
, Genetics summary – VU BMS 2020/2021
Simone Zweers
Reference: Brooker, Genetics: Analysis and prinicples, 7th edition
- Chromosomes = the structures within living ells that contain the genetic material
- Genome = the entire complement of genetic material in an organism or species
- Bacteria, genome is a single circular chromosome
- Eukaryotes, genetic material is found in different cellular compartments
- Human nuclear genome = 22 autosomes, X and (in males) Y chromosomes. Also a mitochondrial
genome
- Chromosomal sequences facilitate four important processes:
o Synthesis of RNA and cellular proteins
o Replication of chromosomes
o Proper segregation of chromosomes
o Compaction of chromosomes so that they fit within living cells
- Transposable elements (TEs) = short segments of DNA which are able to move to multiple sites
within chromosomes and accumulate in large numbers
10.1: Organization of functional sites along bacterial chromosomes
- General features of a bacterial chromosome
- Mostly circular, sometimes linear
- Single type of chromosome, but more
copies can be found within one bacterial
cell
- Few million base pairs
- Few thousand different genes
- Protein-encoding genes = majority of
bacterial DNA
- Intergenic regions = non-transcribed
regions of DNA located between adjacent
genes
- Bacterial chromosomes have one origin of replication = a sequence that is a few hundred base
pairs in length → initiation site for the assembly of several proteins required for DNA replication
- Repetitive sequences = found in multiple copies, interspersed within the intergenic regions
throughout the bacterial chromosome. May play a role in a variety of genetic processes, including
DNA folding, replication, regulation and genetic recombination
10.2: Structure of bacterial chromosomes
- Chromosome is highly compacted and found within a region of the cell = nucleoid
- Bacteria may have one to four identical chromosomes per cell, number of copies
vaires depending on the bacterial species
- Each chromosome is found in its own distinct nucleoid in the cell
- Bacterial nucleoid is not a separate compartment, the DNA in a nucleoid is in
direct contact with the cytoplasm of the cell
The formation of chromosomal loops helps make the bacterial chromosome more
compact
- To fit in the bacterial cell, chromosomal DNA must be compacted about 1000-fold
- Microdomains = loops that emanate from the core are 10.000 bp long. E.coli
chromosome has about 400-500 microdomains
- many microdomains are further organized into macrodomains, 800/1000 kbp
long, 1 macrodomain = 80/100 microdomains
- nucleoid-associated proteins (NAPs) needed for the forming of micro and
macrodomains → DNA-binding proteins, facilitate chromosome compaction and
organization
o they bend the DNA or act as bridges
o facilitate chromosome segregation
2
