Chapter Three: Cell Division Flashcards
What does mitosis function in?
Growth and repair of body cells
What is the difference between mitosis and meiosis?
Mitosis: produces two genetically identical daughter cells with the same chromosome number (diploid 2n) as the parent
Meiosis: produces gametes (sexually producing organisms) with half the chromosome number (haploid n)
What is the structure of a chromosome?
Highly coiled and condensed strand of a DNA molecule
What does a replicated chromosome consist of
Two sister chromatids, where one is the exact copy of the other. A centromere is a specialised region that holds the chromatids together
What is the cell cycle?
A regular sequence of growth and division
What about the phases of the cycle are crucial to an ogransims growth, development and maintenance?
The rate and timing
What is the phase nerve and muscle cells permanently in on losing the ability to divide?
G0
What are internal regulators?
Proteins which make sure that the cell does not undergo mitosis until certain conditons are met
Give an example of external regulators and what they do in the cell cycle
Proteins such as growth factors speed it up, slow it down, or stop it
What happens between stages of the cycle?
There are checkpoints where specialised proteins assess that the cell is ready to proceed to the next phase
What is G1 or the first gap phase?
The newly divided cell enters this p after mito and during G1 the cell increases in size and prepares to replicate DNA
What is G1 checkpoint?
If the cell is healthy, with enough resources, and undamaged DNA, growth factors stimulate it to proceed to S phase.
If not, the cell dies or enters resting state/G0
What is the S phase?
DNA synthesis through the process of replication
What is S checkpoint?
S phase is continuously monitored for replication errors. If it correctly progresses, growth signals stimulate cell to go to G2
What is G2 or the second gap phase?
Cell has to produce organelles/cellular components that will populate TWO new functioning daughter cells
What is G2 checkpoint?
All chromosomes must be fully replicated with no types of damage. Only then can a cell enter M phase and divide
What happens when errors do, though rarely, occur during division?
Development of cancer
90% of cells life spent in interphase. Which phases make up interphase and what is it, and what is seen?
G1, S, G2
Chromosomes replicate in preparation for division.
1/+ nucleoli become visible but nuclear membrane is intact
What is mitosis?
The division of nucleus
What are the 4 phases of mitosis?
Recall acronym
P rophase
M etaphase
A naphase
T elophase
What are the 5 parts of the Prophase?
1) chromosome stands begin to condense and become visible
2) nuceoli disappear
3) spindle fibres begin to form in cytoplasm, extending from one centrosome to other
4) centrosomes begin to migrate to poles
5) nuclear membrane begins to disintegrate
What are the 3 steps in Metaphase?
1) chromosomes line up in a single file on the equator aka Metaphase plate
2) centrosomes are at opp poles
3) spindle fibres run from centrosomes to centromeres of chromosomes
What happens in Anaphase, the shortest?
1)centromeres of each chromosome begin to separate and spindle fibres pull the sister chromosomes apart
What 3 things happen in Telophase?
1) chromosomes cluster at opp ends and the nuclear membrane reforms
2) supercoiled chromosomes begin to unravel and return to their pre-divisiom condition as long threadlike stands
3) nuclear membrane reforms
What is cytokinesis?
Division of the cytoplasm
How does cytokinesis happen in animal cells?
Cleavage furrow form down the middle of the cell and the cytoplasm picked inward and the daughter cells separate
How does cytokinesis happen in plant cells?
A cell plate forms down the middle of the cell. Daughter cells do not separate, but adjacent cells are cemented together by a sticky middle lamella
What is meiosis?
A form of cell division in which cells having diploid chromosome no (2n) produce gametes (sex cells) with haploid chromosome no (n)
What is the difference in functions of mitosis and meiosis?
Mito- growth and repair
Meio- production of gametes
What is meiosis 1 called?
Reduction division
What is a homologue?
Homologous chromosomesare made up of chromosomepairs of approximately the same length, centromere position, and similar versions of genes/alleles
What is synapsis?
Chromosomes pair up precisely with their homologues to prepare for crossing over
What is crossing over and why is it important
Homologous chromatids exchange genetic material. Ensures greater variety in gametes
If homologous chromosomes fail to separate after crossover what is it called?
Nondisjunction
If there are two chromatids after replication in S phase, how many chromosomes?
One
Which structures replicate OUTSIDE the nucleus also during interphase?
Centrosomes (composed of centrioles at right angles, centrioles have microtubules)
State how the state of DNA changes from interphase to prophase
Interphase: DNA in the form on chromatin replicates
Prophase: chromosomes strands become visible
How does DNA change to chromosomes
DNA wraps around proteins called histones and formed nucleosomes. These units coil together, and coil again to form supercoils. These supercoils are chromatin fibres. These fibres condense to form chromosomes which when replicated are chromatids
What is the centre of the centromere called where some of the spindle fibres attach in order to pull the 2 chromatids away
Kinetocore (protein structure)
After sister chromatids are pulled apart what are they called?
Sister chromosomes
State the composition of chromatin
DNA + structural proteins ie histones
Structure of a chromosome :
A strand of DNA tightly wrapped around itself
Why is DNA in chromatin form most of the time?
Otherwise replication and transcription etc of proteins would’ve been difficult
Which enzyme separates 2 strands of DNA?
Helicase
How is mRNA made
DNA is unwinded, on the template RNA bases join (thymine-uracil)
Explain how a diploid cell divides by meiosis to give 4 haploid cells in BREIF
The cell divides into 2 haploid cells by meiosis 1, then these 2 divide to another 4 haploid cells by meiosis 2 (similar to mitosis)
How does Prophase differ in mitosis and meiosis 1?
(After replication in interphase, chromosomes became visible)
Mitosis - identical chromosomes line up in a single file
Meiosis 1 - homologous chromosomes pair up for crossover of alleles
During meiosis 1 in Metaphase 1 what adds to variation apart from genetic material exchange in Prophase 1?
Chromosomes are randomly lined during Metaphase.
This makes each gamete unique
What is the key difference between mitosis and meiosis in Anaphase?
- Mitosis chromatids are pulled apart
- Meiosis 1 entire chromosomes are pulled, this is what halves the chromosome no
What is meiosis 2?
It is the replication of the haploid cells from meiosis 1 by pulling apart sister chromatids producing 4 genetically unique haploid cells
What is one significant difference between Metaphase 1 and 2?
1: chromosomes line up in double files also random (homologues)
2: they line up in single files
Animals have centrosomes, plants don’t. What do they have?
Microtubule organizing regions
