pro euk l Flashcards
euk vs pro: cell size
euk: larger, 10 to 100 micrometers
prok: smaller, 0.5 to 5 micrometers
euk vs pro: nucleus
euk: nucleus with nuclear envelope presemt
pro: no true nucleus
euk vs pro: genetic material
euk:
Linear DNA associated with many proteins;
Found in membrane bound nucleus;
No plasmids
pro:
Circular DNA associated with few histone-like proteins;
Found in a region of the cytoplasm known as the nucleoid region;
Plasmids present
euk vs pro: type of ribosomes
euk: 80S, may be attached to ER or free in cytoplasm
pro: 70S, only found in cytoplasm
euk vs pro: organelles present
euk: many membrane bound organelles present
pro: no membrane bound organelles
euk vs pro: cell walls
euk: composed of cellulose in plants
pro: composed of peptidoglycan
euk vs pro genome: size
euk: larger with more base pairs (10^7 to 10^11)
pro: smaller with less base pairs
(10^4 to 10^7)
euk vs pro genome: appearance
euk: multiple, linear molecules
pro: single, circular molecule
euk vs pro genome: molecule
both are double helix DNA
euk vs pro genome: association with proteins
euk: large amounts of genome is associated with histones, scaffold proteins
pro: less amounts of genome is associated with histone-like proteins
describe level of DNA packing/coiling in eukaryotic genome
high level:
negatively charged DNA double helix is associated with positively charged histones via electrostatic attraction: DNA is wound
around 8 histone proteins twice to form nucleosomes with linker DNA joining adjacent nucleosomes, forming a 10nm fiber/chromatin, which
coils around itself to form 30nm fibre/solenoid
the solenoid forms looped domains when associated with scaffold proteins, forming 300nm fibre, which then supercoils to form metaphase chromosome (at metaphase)
describe level of DNA packing/coiling in prokaryotic genome
Relatively low:
DNA double helix is folded into looped domains by protein-
DNA associations
the looped domains further undergo supercoiling with the help of DNA gyrase and topoisomerase
why do we need to package and coil DNA
- to compact DNA to fit into the nucleus in eukaryotes or nucleoid in prokaryotes
- to prevent DNA breakage or damage since DNA molecules move around alot during nuclear division
- for regulation of gene expression in eukaryotes
euk vs pro genome: location
euk: nucleus
pro: non membrane bound nucleoid region
euk vs pro genome: presence of extrachromosomal DNA
euk: yes if mitochondrial and chloroplast circular DNA are considered
pro: yes of which are plasmids
euk vs pro genome: number of genes
euk: 25000
pro: 4500
pro vs euk genome: presence of introns
euk: many
pro: rare
pro vs euk genome: presence of promoters
both have promoters present
pro vs euk genome: presence of repeated sequences
euk: many such as telomeres/centromeres
pro: rare
pro vs euk genome: presence of enhancers/silencers
euk: common
pro: rare
pro vs euk genome: presence of operons
euk: few
pro: many
describe structure of introns
- non coding DNA sequences found within a gene, specifically
between exons in a specific
segment of DNA (also present in
pre- mRNA) - only in eukaryotes
describe function of introns
- enables a process
called ‘alternative RNA splicing’
to occur where different combinations of different exons
of a single pre-mRNA can be
joined such that different
mature mRNAs are produced
so that one gene can now code for more than one polypeptide
describe structure of promoter
- located just
upstream of the
transcription start
site of a gene, hence it is called a proximal control element - has critical elements
e.g.1. TATA box, loacted
upstream of transcription start
site)
e.g. 2. CAAT and GC boxes, located upstream of TATA but are not always present and are not critical in determining transcription frequency
describe function of promoter
- recognition & binding site for
general transcription factors which then recruits RNA
Polymerase to form transcription
initiation complex which initiates
transcription
-TATA box in promoter is where general transcription factoers bind to so it determines precise location of transcription start sitet site - CAAT and GC box improves the efficiency of promter
describe structure of enhancers/silencer
are non coding regulatory DNA sequences
usually located far away from the
promoter (usually much further
upstream or downstream), hence being called a distal control element
describe function of enhancer
- recognition & binding site for
activators - increase the frequency of
transcription by promoting the
assembly of the transcription
initiation complex
(with the help of
DNA bending
proteins that bend
spacer DNA)
describe function of silencer
- recognition & binding site for
repressors - decrease the frequency of
transcription by
preventing the
assembly of the
transcription
initiation complex
what are specific transcription factors?
proteins with a DNA binding site that is complementary in shape and charge to a specific regulatory sequence of DNA which it binds to
structure of telomeres
1- found at both ends/terminals of linear, eukaryotic chromosomes
2- non-coding DNA made up of a series of tandem repeat sequences which are a specific sequence of nucleotides occurring many times in a row
3- in humans, each repeat has
the sequence 5’ TTAGGG 3’
4- have a single stranded region
at their 3’ ends known as the 3’
overhang and which due to a limitation of DNA polymerase,
this region of DNA does not have acomplementary strand)
describe role of telomeres in the end replication problem
Telomeres ensure that genes are not eroded and vital
genetic information is not lost with each round of DNA replication due to the end replication problem.
As DNA polymerase requires a free 3’OH of a pre-existing strand to add nucleotides, the last RNA primer on the lagging strand with DNA cannot be replaced with DNA. Hence, the DNA molecule shortens with each round of
replication. Telomeres, which are non-coding sequences at the ends of linear chromosomes will be lost before any vital genetic information is. Since
telomeres are non-coding, they can be lost without any deleterious effect.
describe the role of telomeres in stabilising ends of chromosomes
2-Telomeres protect and stabilize the terminal ends of chromosomes by forming a loop using the 3’overhang.
This prevents single-stranded terminal end of one chromosome from annealing to a complementary single-stranded terminal end of another
chromosome, prevent fusing of 2 chromosomes.
The formation of the loop also prevents the cell’s DNA repair machinery from detecting the chromosome as damaged DNA (i.e. double stranded
breaks) and trigger apoptosis.
describe telomere’s role in their own extension
3-Telomeres allow their own extension, as they have a 3’ overhang which provides an attachment point for the correct positioning of the enzyme
telomerase. Although telomeres shorten with every round of DNA replication, telomerase activity in germ cells, embryonic stem cells and cancer cells can
maintain telomere length.
how does telomerase work
A short 3-nucleotide segment of RNA within telomerase binds to part of a DNA repeat in the 3’overhang by complementray base pairing.
2. The adjacent part of the RNA within telomerase is used as a template to synthesise a short
complementary 6-nucleotide DNA repeat.
3. Telomerase catalyses the formation of the phosphodiester bonds between the existing
3’OH group of existing DNA overhang and 5’ phosphate group of incoming deoxyribonucleotide
After the repeat is made, telomerase translocates 6 nucleotides to the right in the 5’
to 3’ direction of the DNA overhang and begins to
make another repeat. The above process is repeated such that a series of tandem repeats are
made, elongating the telomere.
5.Then primase makes an RNA primer near the end of the telomere. DNA polymerase adds
nucleotides to the 3’OH end of the primer and hence synthesizes a complementary strand . The nick is then sealed by ligase. The RNA
primer is eventually removed.
structure of centromeres
- Constricted region on chromosome where kinetochore
microtubules attach during
nuclear division
2- non-coding DNA made up of a
series of tandem repeat sequences
function of centromeres
1- allow sister chromatids to
adhere to each other
2- allow kinetochore proteins to attach and which in turn
allow spindle fibres to attach so
that sister chromatids/homologous
chromosomes can align along the
metaphase plate and subsequently be separated to
opposite poles.
Ultimately, allow s
proper alignment and
segregation of
chromosomes.
