Chapter 6.1 cell Cycle Flashcards
What are three stages of cell cycle? (Or two)
First is interphase, where there is long periods of growth
Then is the mitotic division stage consisting of mitosis and cytokinesis
What happens in interphase roughly (3)
- why is it referred to as a resting phase but what actually is it
- Long periods of growth and a cell spends most of the cell cycle here
- Preparation for division
- normal functions like respiration still carried out
-2)people refer to interphase as the resting phase, however this is NOT TRUE.
: it actually is a very active phase of cell cycle as cell carries out all replication including producing enzymes hormones etc, whilst actively preparing for cell division
What happens in first stage
G1- First growth phase ,
- proteins that make organelles are synthesised
- ALL organelles APART FROM CHROMOSOME then duplicate (including mitochondria / chloroplasts )
- CELL increases in size
What happens in second stage and what called
S Phase (synthesis of DNA ) - here DNA in chromosomes is fully replicated in the nucleus
What happens in last phase (what called)
G2= second growth phase
- here cell continues to increase in size
- energy stores increase (ATP)
- proteins needed for cell division made
Then G2 check happens
What is full order of Interphase?
G1 G1 CHECKPOINT S Phase / G0 Phase G2 G2 checkpoint
When are checks for interphase and what is checked?
What does it do
G1 Check, at the end of G1 and bringing of S
- checks for cell size, nutrients growth factors and DNA damage
- proteins including helicase etc for s phase
2) G2 check at the end of G2 before mitosis
- checks for whether DNA HAS BEEN REPLICATED CORRECTLY
- checks for any damage to DNA and duplicated
- fixes these makes repairs
- checks for cell size
If check not complete not allowed to go into next stage
What is the G0 phase
Why do they enter here (2)
What does SENSECENT ! mean and how is this linked with old age ?(also normal cells how many times they can divide
What cells can return from G0
Phase given to the stage where the cell leaves the cell cycle , temporarily or forever,
1) - if a cell becomes specialised it has differentiated to perform a specific function where it does this indefinitely and thus NO LONGER DIVIDES
- the DNA of a cell may have become damaged so it is no longer viable . The cell is permanently under cell arrest in G0 and NO LONGER DIVIDES (still alive tho )
2) senescence is the inability to divide . the majority of cells only able to divide a few times and end up becoming senescent . As you grow old the number of this INCREASES and this is linked with diseases
3) cells like liver few times and lymphocytes
What is the ACTUAL definition of mitosis (which sets it aside from cytokinesis )
The division of the nucleus , (rather than physical division)
When and why does mitosis happen
Does mitosis happen In prokaryotes ?
Mitosis happens when the two daughter cells need to be genetically identical
- thus in the case of growth , repairing tissue and replacement of cells
- asexual reproduction to give genetically identical offspring
2) NO THIS IS BINARY FISSION
What is the structure of DNA MOLECULES (chromatin how) before going into mitosis and as a result of interphase ?
Why held at centromere
By now DNA has replicated
1) IN INTERPHASE dna combines with proteins (cohesion ) and histone to make a Long thin molecule called chromatin which is loosely coiled and csn’t see under microscope
2) all the chromatin now converts into two strands called CHROMATIDS that are joined together in the middle at the CENTROMERE (one chromosome made up of two adjacent chromatids)
- two adjacent chromatids of the same CHROMOSOME are called sister Chromatids
2) it is essential they held in the middle so that they can be manoveured around and segregated equally at the end
What happens in early prophase?
2) CHROMATIN MOLECULES NOW CONDENSE AND APPEAR AS CHROMOSOMES!
- the Nucleolus (responsible for RNA synthesis ) breaks down
- the NUCLEAR MEMBRANE begins to breakdown , leaving chromosomes free in cytoplasm
- mitotic spindle fibre begins to be made , and centrioles move to opposite ends of the cell
What happens in late prophase / pro metaphase
Here microtubules invade the nuclear area as they extend to each centromere , beginning to pull
- by the end of prophase the nuclear membrane is fully broken down
- chromosomes condense even more (now can take up stain and be seen on microscope)
What happens at metaphase?
WHAT ELSE ? (Why this important to happen)
Chromosomes (Esch With two chromatids) are moved by the spindle fibre to the centre of the cell , called the METAPHASE PLATE (equator and equidistant from cell poles) with the centromeres at the centre
+ THEN METAPHASE SPINDLE FIBRE CHECKPOINT HAPPENS
- here it is checked every single chromosomes is attached to each spindle fibre correctly.
- this important because if not you could get an uneven distribution of chromosomes in each resulting cell Causing complications
What happens at anaphase
- the centromeres holding pairs of chromatids now divide
- this allows the spindle fibres to pull on the divided centromeres by CONTRACTING
- thus pulling sister chromatids to opposite pole of the cell (gives v shape)
Now chromosomes are at each end of the cell
