Week 3: Genomes & Chromosomes; DNA Replication Part I Flashcards
What is a genome?
The entirety of an organism’s hereditary material, for living things this would be DNA
True or False: Some viruses have RNA as hereditary material
True AND False - some have DNA!
Approximately how many base pairs long is an E.coli’s genome?
~ 46 mil BP long
True or False: Human mitochondrial genome is smaller in comparison to E.coli
True
Mitochondria has its own DNA, but it is very small, why?
Some mitochondria DNA got to nuclear DNA
In the human genome, how many base pairs are there per genome?
Approx. 3 BILLION
How many chromosomes do we get per parent?
23
How many genomes do we /technically/ have per cell?
2! One from each parent, which means we have about 6 BILLION BPs in each cell
Describe the correlation between genome size and organism size/organism complexity/# of genomes
Genome size is not always correlated with any of them
List the different parts of the human genome by organizing them into repeated sequences and unique sequences
Repeated sequences:
- LINEs
- SINEs
- DNA-only transposon
- Simple repeats
- Segment duplications
Unique Sequences:
- Nonrepetitive DNA that is in neither introns nor exons
- Introns
- Protein-coding exons
What is the approximate percentage of your genome that encodes proteins?
Less then 1%
What does LINEs stand for? SINEs?
LINEs = Long Interspersed Nuclear Elements
SINES = Short Interspersed Nuclear Elements
What are mobile genetic elements?
Sequences that sometimes cut themselves out, sometimes copy, sometimes paste themselves back in
What is an example of simple repeates?
CAG, GAG, ACG, etc. repeated 30x
What are segment duplications?
1000s - 100,000s of BPs that are duplicate
What are introns?
Introns are nucleotide sequences that get transcribed + get spliced out of RNA
What are exons?
Exons are nucleotide sequences that help determined which RNA get transcribed in which cells and how much
What occurs when a cell is in a NON-packaged state
Even the small prokaryotic genome would occupy a considerable portion of the cell volume
How is DNA packaged in prokaryotes?
Since prokaryotes do not have a nucleus, DNA folds around proteins. This forms the prokaryotic nucleoid.
What mechanism allows you to see chromosomes in different colours?
Chromosome painting hybridization (CPH)
What does FISH stand for? And what is it?
FISH: Fluoresence In Situ Hybridization. FISH is a diagnostic technique to detect the presence of a specific sequence
How many chromosome pairs do humans have?
23 pairs
What makes up a chromosome?
A single, long linear DNA molecule and associated proteins, called Chromatin
Chromatin is ________
DYNAMIC (which means you can condense/decondense it)
How does a mitotic chromosome differ from an interphase chromosome?
An interphase chromosome contains one long strand of DNA while a mitotic chromosome has two, making it a duplicated chromosome
What makes up a chromosome undergoing mitosis?
Two sister chromatids with a centromere at the center
Most of a chromosome is at which level of organization?
30 nm fibre
Describe a nucleosome
The DNA wraps around a histone once then another 2/3 time
What is a histone? What is their charge?
Small proteins that are rich in lysine and arginine. They have a positive charge which neutralizes the negative charge of DNA
What are the parts of a histone?
Four core histone proteins: H2A, H2B, H3, and H4 (there’s a pair of each in the octamer core)
One linked histone: H1
What keeps DNA on the histone?
The histone H1 acts like a paper clip that clips the DNA on
What makes up a nucleosome core particle?
Core histones + DNA around it
What makes up a nucleosome?
Nucleosome core particle + H1 + linker DNA
What is involved in forming chromatin loops?
Sequence-specific clamp proteins and cohesins
As a cell enters mitosis, what replaces cohesins? What do they form and for what reason?
CONDENSINS replace most cohesins. They form double loops of chromatin to generate compact chromsome.
What is the final result of packaged DNA relative to DNA’s extended length?
DNA packaged into a mitotic chromosome is 10,000 times shorter than its extended length
True of False: Packing and unpacking DOES NOT require ATP, but rather another form of energy
FALSE!
Can there be changed made to chromatin? If so, what kinds of proteins can do this?
Changes can be made to chromatin structure by chromatin remodeling complexes and histone modifying enzymes
What are the names of the two degrees of chromatin condensation?
Heterochromatin and euchromatin
Which levels of chromatin does heterochromatin lie under?
30 nm and more
Which levels of Euchromatin lie under?
Beads-on-a-string and less
Explain what heterochromatin is
Heterochromatin is HIGHLY condensed chromatin. They can be found in meiotic and mitotic chromosomes. They include centromeres and telomeres. They are not always highly condensed
Explain what euchromatin is
Euchromatin is relatively NON-condensed. They are not always loosely condensed. They can be active (transcribing/replicating) or not.
What is the difference between heterochromatic and euchromatic regions of interphase chromsomes?
Heterochromatic regions of interphase chromosomes are areas where gene expression is SUPRESSED while in euchromatic regions there are EXPRESSED
What is responsible for modulating the REVERSIBLE switching from euchromatic to heterochromatic regions along chromosomes?
Localized covalent modification of histones, the presence of chromatin remodeling complexes, and RNA polymerase (transcription) complexes
True or False: Interphase chromosomes organize in specific areas of the nucleus
True
What is the difference between when a gene is off and on within chromatin?
When a gene is off the area in which is lies it too condensed for RNA to read. When a gene is on, the area is less condensed.
What were the two ways of thinking about DNA replication back then? And what did they suggest about DNA replication?
Two ways of thinking:
1: DNA synthesis is CONSERVATIVE. Which means that when the parental strands replicated, one daughter cell will have both parental strands and the other daughter cell will have two new strands
2: DNA synthesis is SEMICONSERVATIVE. Which means that when the parental strands are replicated, both daughter cells have one new strand and one parent strand.
What are the three rules of DNA replication?
- DNA is antiparallel
- New DNA is synthesized from 5’-3 (meaning you add onto the 3’ end)
- The template (parent strand) is read 3’-5’
What is the difference between leading and lagging strands?
Leading strands are made towards and end of separation. Lagging strands are made in the opposite direction of an end of separation.
What results from lagging strands?
Okazaki fragments
True or False: DNA grows in both directions after the origin of replication
True!
At each origin of replication, how many DNA replication strands are there?
4: 2 leading strands and 2 lagging strands on either parent/template strand
Where does DNA replication start?
There are specific regions on DNA that are easier to open. These region are A-T rich since they only share 2 H-bonds (in comparison to G-C’s 3 H-bonds). This region is recognized by an initiator protein that binds to DNA.
How many origins of replication do bacteria have? Eukaryotes?
Bacteria have one origin of replication, eukaryotes havemultiple
How does DNA replication proceed in bacteria?
From the singular replication origin, a new circular genome is created
The replication fork is _________
asymmetrical
Leading strand is replicated ___________. Lagging strand is replicated _____________.
continuously; discontinuously
