L01 Meiosis Flashcards
All cells share:
- DNA(genetic material)
- Plasma membrane
- Ribosomes
Discuss living organisms that have genetic material(not including viruses)
- Prokaryotes( bacteria and archaebacteria)
- Eukaryotes (Animal, plant, fungus, protist(eukaryotic cell that is not one of the others))
Describe the cell structure of prokaryotic cell
- Prokaryotes are typically a unicellular organism
- surrounded by plasma membrane
- PM protected by cell wall
- Prokaryotes contain no organelles, DNA and proteins and lipids are free in the cytoplasm
- cell wall surrounded by a capsule (or slime layer or glycocalyx ) made up of polysaccharides and glycoproteins
- ribosomes in cytoplasm
Describe DNA in a prokaryotic cell
DNA is organized in a nucleoid region in the cytoplasm
Semi circular DNA call the plasmid is also found in the cytoplasm, this is not genomic DNA
Briefly describe reproduction in prokaryotes
Cell division in prokaryotes is asexual reproduction very similar to mitosis
Describe how prokaryotes transmit genetic material
DNA is first replicated by enzymes and substrate(deoxynucleotides)
DNA molecules separates in to two cells
Also known as binary fission (act of dividing or splitting into two)
Daughter cells is exactly like the parent cell, same amount of DNA
Describe the cell structure of the eukaryotic cell
- Cell surrounded by a cell membrane
- Free ribosomes in cytoplasm but there is also on the rough endoplasmic reticulum
- mitochondria
- nuclear envelope: membrane barrier separating the nucleus from cytoplasm
- centrioles
Describe the centrioles of eukaryotic cells
2 cylindrical structures made of a protein tubulin and surrounded by a pericentriolar material, during cell division the pericentriolar material contains proteins that help with spindle fiber assembly
What are somatic cells ?
In animals, reproductive cells give rise to spermatozoa and ova
Somatic cells are all other cells
How do eukaryotes transmit genetic materials?
On chromosomes via mitosis and meiosis
Give a brief description of meiosis
Meiosis leads to the production of sex cells
-gametes or spores with half the genetic material of the parent cell(half the chromosomes, haploid)
Give a brief description of mitosis
Mitosis leads to the production of two cells from the parent cell
- each with the same amount of genetic material as the parent cell - Walther Fleming , German anatomist named this because he saw the formation of paired threads
How are chromosomes converted to chromatin?
When the cells are not dividing, the chromosomes are diffuse within the nucleus and it is chromatin
What happens when it is time for the cell to divide?
- the DNA duplicates
- the DNA starts to become organized, gets packed and becomes organized to the condensed chromosome structures we recognize by distinctive shape and sizes
In diploid organisms, chromosomes exit in …..
Homologous pairs
Explain the aspects of homologous chromosomes
- similar but not identical
- one from each parent (biparental inheritance)
- homologous pairs carry all the same genes
- sometimes slight difference between mom and dads genes
Homologous chromosomes pairs carry all the same genes, elaborate on this
- Identical regions along a chromosome are called a locus
- this is true for 22 chromosomes that are called autosomes
- the exception is the sex chromosome pair, X and Y chromosomes which have some unique, sex determining genes
Describe how many chromosomes are in humans
Somatic cells have homologous chromosomes
Humans have 46 chromosomes (23 homologous pairs )
This is the human diploid number(2n)
What are meta centric chromosomes?
Chromosomes with the centromere located in the middle
What are submetacentric chromosomes?
Chromosomes with the centromere located between the middle at the end
What are Acrocentric chromosomes?
Chromosomes with the centromere located close to the end
What are telocentric chromosomes?
Chromosomes with the centromere located at the end
Seen in mice, not in humans
What are holocentric chromosomes?
Centromere consists of the entire length of the chromosome
Seen in C elegans, not in humans
The top, petition arm of the chromosome is the …
P arm
The bottom, longer arm is the…
q arm
What happens in metaphase?
The DNA is duplicated, two copies of the same chromosome
Two copies of the same chromosome attached by a centromere are called…
Sister chromatid
Describe a Karyotype
The metaphase chromosomes from a cell are photographed and the chromosomes are cut out and organized based on chromosome shape.
Describe sex determining chromosomes
- Not homologous in size
- Not homologous in centromere placement
- Y lacks most of the gene loci that X has, as it is smaller
- Must contain homologous REGIONS to behave as a Homologous chromosomes during meiosis
- Not homologous in arm ratio(p and q)
How are chromosomes treated for Karyotyping and why?
Chromosomes treated with a protease so that the sister chromatid are only a associated at the centromere
Then stained with Geimsa
What is a zygote?
A single celled fertilized egg of multicellular organisms
The fertilized egg will now enter the cell cycle
What is cytokinesis?
The part of the cell cycle, cytoplasmic division completes the formation of daughter cells
What is karyokinesis?
Part of the cell cycle, when the cell is ready to divide, all of the DNA(46 chromosomes) is duplicated then one complete set is separated from the other set during nuclear division for the formation of daughter cells.
What are the discrete stages of mitosis?
(PPMAT)
P- prophase P- prometaphase M-metaphase A-anaphase T-telophase
State the events of interphase
Two gap phases G1 and G2
- Some cells enter G0 where it withdraws from the cell cycle”quiescent” - G0 is a point in G1 where cells are nondividing but metabolically active - G1 and G2 have intensive metabolic activity and cell growth and cell differentiation
S phase is when DNA is synthesized
Give the time interval/duration of each phase in interphase
G1 - 5 hours
S phase- 7 hours
G2- 3 hours
Interphase is characterized by …
The absence of visible chromosomes
What is the longest part of mitosis?
Prophase
State the occurrences of prophase
- Centrioles divide and move apart to establish poles
- Chromosomes coil, condense and become visible
- Spindle fibers begin to organize at the centrioles
State the occurrences of prometaphase
- chromosomes begin to move to the equatorial plane/metaphase plate of the cell
- Centrioles reach the poles of the cell
- Spindle fibers form and become organized
State the occurrences of metaphase
- Centromeres align at the metaphase plate
- The centromere is attached to two spindles, one from the top and bottom
- Each spindle wants to associate with one sister chromatid
What is the most common phase of mitosis fir Karyotyping.
Metaphase
The migration to the metaphase plate is only possible by the binding of…
The spindle to the chromosome’s kinetochore and centromere region
What is the kinetochore region?
An assembly of proteins associated with the centromere region
What is Cohesin?
a protein complex that holds sister chromatids together
What is Separase?
An enzyme that degrades cohesin
What is Shugoshin?
A protein that protects cohesin from being degraded by separase
State the events of Anaphase
Sister chromatids separate/disjoin- disjunction
Sister chromatids move to the opposite poles of the cell
- Shigoshin must be degraded - Cohesin are cleaved by separase
Separated sister chromatid are now called…
Daughter chromosome
Movement of daughter chromosome is dependent on…
Kinetochore-spindle fiber attachment
State the events of Telophase
- Daughter chromosomes arrive at the poles
- Reformation of the nuclear envelope around each set of chromosomes
- Spindle fibers disperse into microtubules
- Cytokinesis occurs to divide the cytoplasm between the 2 daughter cells
- Daughter cells enter interphase
What may prevent the cell from going from G1 to S?
The environment of the cell is not favorable to proceed to S phase
The cell is not right and DNA is not good
What may prevent a cell from going from G2 to Mitosis?
All the DNA has not been replicated faithfully
The cell environment is not favorable to enter mitosis
What may prevent a cell from going from Metaphase to Abaohase?
The sister chromatids are not ready to separate
Not all the chromosomes are not attached to the spindle and kinetochores
Explain the functioning of the proteins that regulate the cell cycle
Governed by hetero-dimers made of:
- Cyclins
- CDK proteins (cyclin dependent kinases)
These dimers accumulate in the cell at premise times to trigger the cell to proceed to the next stage
How can protein hetero-dimers lead to cancer?
Mutations in proteins, hetero-dimers often lead to cancer/ uncontrolled cell division
Discuss genetic content “n” and chromosome number “c” in mitosis
S phase, G2 and mitosis has 2n and 4c
G1 has 2n 2c
