pro and euk 1-2 Flashcards
(50 cards)
pro (bacteria) vs euk
(cell size, nucleus, genetic material)
euk: larger (10-100microm), nucleus with nuclear envelope, linear double helix dna
pro: smaller (0.5-5 microm), no nuclear envelope, circular double helix DNA`
level of DNA packing / coiling in pro
low level, only folded into looped domains by protein-DNA association and supercoiling that causes further compaction
leve of dna packing/coiling in euk
high level, negatively charged DNA held around 8 positively charged histone proteins via electrostatic interactions – form nucleosomes
and remaining linker DNA is joined to adjacent chromosomes
fibre coils around it self to form a 30nm chromatin fibre that forms looped domains when associated with scaffold proteins + supercoiling also present
pro vs euk (location, plasmids, no genes)
pro: nucleoid region, has plasmids, fewer genes
euk: nucleus, no plasmids, many genes
non coding-regulatory sequences (4)
introns, promoter, enhancer and silencer
non-coding repetitive sequences (2)
telomeres and centromeres
intron structure
ONLY in Euk, within a gene, between exons
intron function
- allow alternative RNA splicing, where all introns and different combinations of exons excised, remaining exons joined together to form different mature mrna
–> one gene codes for more than one polypeptide
promoter structure
- upstream of transcription start site of gene (proximal control element)
- has critical elements e.g. TATA box and CAAT / GC boxes
promoter function
- recognition site for binding of general transcription factors (GTF) and rna polymerase, formin transcription initiation complex to start transcription
- TATA box determines precise location of transcription start site, CAAT and GC boxes promote assembly of TIC
enhancer and silencer structure
located far away from promoter (distal control element)
enhancer function
recognition and binding site for activators (specific transcription factors)
promote assembly of TIC
silencer function
recognition and binding site for repressors (specific transcription factor)
prevent assembly of TIC
telomere structure
- at both ends of linear, eukaryotic chromo
- made up of series of tandem repeat sequences
- have a single stranded region at 3’ ends called 3’ overhang
telomere functions (first role)
- ensure genes not eroded with each round of DNA replication due to end replication problem, prevents loss of vital genetic info
end replication problem
a. During DNA replication, DNA polymerase needs a free 3’ OH of a pre-existing strand to add free nucleotides
b. an RNA primer is synthesised to provide this free 3’ OH end
c. but the RNA primer cannot be removed or replaced w nucleotides, creating the 3’ overhang
d. the ends of the chromosomes hence shorten with every round of replication
e. since telomeres are at the ends and are non-coding, they will be shortened instead of the chromosomes without deleterious effect (loss of vital genetic info)
telomere function (2)
protect and stabilise terminal chromosome ends by forming a loop using 3’ overhang
- prevents annealing of single-stranded terminal end to a comp single-strand of another chromosome, prevent fusing of chromosomes
- also prevents cell’s DNA repair machinery from detecting chromosome as damaged and triggering apoptosis
telomere function (3)
allow their own extension, providing attachment point for telomerase enzyme
-telomerase activity in germ cells, embryonic stem cells and cancer cells can maintain telomere length
centromere structure
constricted regions on chromosomes where kinetochore microtubules / spindle fibres attach during nuclear division
made up of a series of tandem repeat sequences
centromere function (1,2)
- alloe sister chromatids to adhere to each other
- allow kinetochore proteins to attach, and later spindle fibres to attach, so that sister chromatids / homo chromo can be separated to opp poles
(proper alignment n segregation)
3 forms eukaryotic gene regulation
histone acetylation, deacetylation
chromatin remodeling complex
DNA methylation
(+) Histone acetylation
(process, purpose)
addition of acetyl group to lysine in histone by histone acetyltransferase
removes +ve charge on histones, decreasing electrostatic attraction btw negatively charged DNA and histones
makes promoter more accesible to RNA polymerase and GTf, promoting TIC and transcription
(-)Histone deacetylation
(process, purpose)
removal of acetyl groups from histones by histone deacetylase
restores +ve charge on histones, tighter interaction between dna and histones
makes promoter less accessible to RNA polymerase and gtf, preventing assembly of TIC and inhibits transcription
(+/-) chromatin remodeling complex
(structure, 2 functions)
protein complexes that alter structure of nucleosomes temporarily
- makes DNA more tightly coiled around histones, preventing access of RNA polymerase and gtf to promoter …
- makes DNA less tightly coiled around histones, gives access to RNA polymerase and gtf to promoter…
