MolBio4 - 32 Flashcards
What does the word chromosome actually mean?
Coloured body
Where is most eukaryotic DNA stored?
Chromosomes
Other than linear DNA, what does each chromosome also comprise?
Proteins: packaging and folding; controlling replication, repair and recombination; mainting integrity; regulating gene expression
During what phase of mitosis are chromosomes easily distinguished?
Metaphase
What is the term given to the organised represenation of all the chromosomes at metaphase?
Karyotype
What is the karyotype of an organism?
The organised representation of all the chromosomes in a eukaryotic cell at metaphase
Describe chromosome arrangement during interphase
Each occupies a distinct subdomain of the nucleus, and transcriptionally inactive DNA is in the periphery
Describe chromosome movement during transcription
Activation is accompanied by movement from the periphery to the centre, indicative of very high order controls
Describe the general structure of chromatin
Highly coiled - looks like beads on a string - beads are nucleosomes
What are nucleosomes?
Protein core around which DNA coils like cotton on a bobbin
What are the protein subunits of nucleosomes called?
Core histones
How many subunits form a nucleosome?
8
What is special about nucleosome subunits?
Tails that are free to interact with other proteins
What are linker histones?
Proteins that strap DNA onto the core histone octamers and limit movement of DNA relative to the nucleosome
What packaging effet do histone octamers induce?
DNA packaged into compact, flexible 30nm chromatin scaffold that can be remodelled to accommodate protein complexes for gene transcription/replication
What are the two specialised DNA sequences imperative for DNA function?
Telomeres and centromeres
What are telomeres?
Specialist overhanding single stranded TTAGGG repeats at ends of chromosomes, protecting the length of the chromosome, that can be several hundred nucleotides long
What are centromeres?
Location of attachment of the mitotic spindle during cell division, ensuring faithful segregation of sister chromatids
Outline the structure of a centromere
Made up of tandem repeats of alpha-satellite DNA that convey affinity for the kinetochore inner plate proteins. Kineotchore outer plate proteins bind to the inner plate, and then the protein components of the mitotic spindle
What is CENP-A?
Gene that encodes the specialist H3 histone that mediates the attachment of chromsome to kineotchore
What percentage of DNA sequence encodes cellular proteins?
1.50%
What percentage of the human genome is made up of repeated DNA?
50%
What is 50% of human DNA?
Repeated copies of retrotransposons known as parasitic DNA
What are transposons?
Mobile genetic elements that jump around the genome
What are the three types of transposons?
DNA, retroviral and non-retroviral polyA
Why are DNA transposons important?
They confer the ability to mass re-arrange DNA
How do DNA transposons work?
Mover around by ‘cut-and-paste’ WITHOUT self-duplication
How do retro-viral transposons work?
Replicate by RNA intermediates producing new DNA copies that integrate at new genomic locations using self-encoded reverse transcriptase
Outline the process of retro-viral replication.
Entry into cell > loss of envelope > single RNA > RNA/DNA > DNA double helix > integration > transcription > translation > more virus to infect organism
Where are polyA retrotransposons commonly found?
Verterbrate genomes
How do polyA retrotransposons replicate?
Via RNA intermediate using retro-transposon-encoded reverse transcriptase
Outline the polyA retrotransposon replication mechanism
Element transcribed and translated to produce reverse transcriptase which then binds back onto the element. This then cleaves the first strand of target DNA, and reverse transcribes the RNA into the genome. Multistep process produces second DNA strand with element copy at new position
