Chromosomes & mitochondrial Genetics Flashcards
Human Genome & chromosomes
DNA molecules are extremely long, orderly and compact three-dimensional structures
human genome consists of 3 billion nucleotide base pairs
of DNA organized into 23 chromosomes
Each diploid human cell contains two full complements of the
human genome
• As diploid organisms, humans inherit a haploid set of
genes (23 chromosomes) from each parent
• 2 copies of every gene – one maternal and one
paternal
• The exception here would be on the X and Y
chromosomes
chromososme
A nucleic acid structure bound by protein containing all or a portion of an organism’s genetic information
- DNA & protein
Each chromosome is a single length of DNA with a stretch of
short repeats at the ends called telomeres
• They have additional repeats in the centromere region
Chromosome Structure- chromatin
Each chromosome is a highly ordered structure of a single dsDNA
molecule, compacted many times with the aid of structural proteins
Composed of DNA and histone proteins
• Nuclear DNA in conjunction with its associated structural proteins –
including histone and non-histone proteins
Arranged and organized so that the degree of condensation
increases with higher levels or structural organization
• Generally, less condensed during interphase (when DNA is
replicated)
Chromosme structure- Nucleosome
most basic level of chromatin organization and is present
as repeated units along the full length of each chromosome
Each nucleosome unit consists of a nucleosome core particle
and base pairs of linker DNA, which spans between adjacent nucleosomes
• A nucleosome core particle involves 146 base pairs of dsDNA
tightly wound around an octamer of histone proteins
- This octamer of histone proteins is made up of two each of four histone proteins:
- H2A, H2B, H3, H4
Euchromatin
• Genomic regions that are rich in genes
• Generally, less compactly organized
- stains lighter
- easy for transcription
Heterochromatin
- more difficult to transcribe
- Regions that are gene-poor or span over transcriptionally silent genes
- More densely packed and organized
Important for:
• Maintenance of specialized chromatin structures
• X-chromosome inactivation in females
• Maintenance of genome stability by stabilizing repetitive DNA sequences
• Regulation of gene expression
Besides the large centromeric and telomeric blocks of
heterochromatin, smaller domains of heterochromatin
are scattered throughout the genome and are
associated with the control of gene expression
Centromeres
specialized regions of heterochromatin
Has an important role in directing movement of
chromosomes between daughter cells during cell
division
Telomeres
specialized regions of heterochromatin
Contains repetitive nucleotide sequences that are
located on, and protect, the ends of the chromosomes
Bacterial Genetics
Most bacteria possess one chromosome
• Usually consists of a long, circular, continuous, double-
stranded DNA molecule, with no protein
single chromosome replicates just before cell
division by binary fission and both daughter cell have
exactly the same genetic composition as the parent
cell
Plasmids are small circular molecules of DNA that are not
part of the chromosome (extra-chromosomal)
Mitochondrial Genetics comes from where
In eukaryotic cells, there is second genome of importance – the
Mitochondrial genome
Mitochondrial DNA is transmitted between generations by maternal
inheritance, with the mitochondria coming from the oocytes and not
typically from sperm
• The human mitochondrial genome is a circular piece of DNA
Multiple copies of mitochondrial DNA are present within each
mitochondrion and each cell contains a variable number of mitochondria, depending on the energy requirement
what makes mitochondrial DNA attractive for tests for which sample
DNA is limited
Some cells may contain several thousand copies of mitochondrial DNA
ex.Crime scenes, pathogen detection, paleontology
Mitochondrial DNA design
Mitochondrial DNA is double stranded except at the replication and
transcription control region – the D-loop
The mitochondrial genome codes for:
• 13 polypeptides
- All involved in the oxidative phosphorylation pathway
• Two rRNAs
• Three of the 22 tRNAs required for mitochondrial protein synthesis
Several other proteins are also required for normal mitochondrial function ( can’t code for everything it needs by itself)
Problems when genetic analysis is performed for mitochondrial DNA
can be potential problems related to the presence of nuclear pseudogenes – DNA segments in the nuclear genome with significant homology to the mitochondrial genome
- The close resemblance of the nuclear and mitochondrial DNA segments may result in the false-positive detection of sequences
- Therefore, the specificity of PCR systems for mitochondrial DNA detection needs to be carefully evaluated
Mitochondrial Genetics - Mutations
mutation rate of mitochondrial DNA is 10-20 times higher than that of nuclear DNA
possibly due to poor fidelity of mitochondrial DNA polymerase
Germline mutations in the mitochondrial genome generally lead to neurodegenerative and or myopathic
diseases
Somatic mutations are associated with aging and cancer development
Mutation populations
Due to the accumulation of mutations, more than one population of mitochondrial DNA sequences may be present in a cell
