lecture 8 - cell division Flashcards
what types of cell division is there?
unicellular organisms - reproduce by cell division - commonly through binary fission multicellular organisms depend on cell division for: - development from a fertilised cell -growth -repair -cell division occurs via mitosis or meiosis
describe cell division
- results in genetically identical daughter cells
- cells duplicate their genetic material before they divide, ensuring that each daughter cells receives an exact copy of the genetic material, DNA
- the DNA molecules in a eukaryotic cell are packaged into chromosomes
- eukaryotic chromosomes consist of chromatin, a complex of DNA and protein that condenses during cell division
describe cell division in animals
- somatic cells have two sets of chromosomes (one set from each parent). they all have the SAMe chromosomes
- gametes (germ cells/ova + sperm) have only one set of chromosomes. these are produced by a special type of cell division called meiosis
what happens in prokaryotic cell division?
binary fission
- asexual reproduction where a cell expands and then divides in two.
- in bacteria, DNA is free-floating in the cytoplasm, and does not have a membrane- bound organelles.
- very important to replicate the DNA so that the daughter cells have identical genetic information
>binary fission does not occur indefinitely for all bacteria
- growth limited by number of nutrients available to the bacteria
- also may choose to enter dormancy
what happens in eukaryotic cell division?
- eukaryotic cells usually have more DNA than prokaryotes
- this needs to be condensed and packaged into chromosomes
- this is a carefully coordinated complex process that occurs via a cell cycle and mitosis
what happens to chromosomes during cell replication?
- each duplicated chromosome has two sister chromatids which separate during cell division.
what is a centromere?
- site where the two chromatids are held together
- reduce complexity of sorting task
- keeps pairs together
briefly describe the stages in the eukaryotic cell cycle
two phases
- interphase (G1,S and G2)
- mitotic phase (M)
describe the mitotic phase
consists of
- mitosis, the division of the nucleus
- cytokinesis, the division of the cytoplasm.
- typically lasts only 30-60min. (depending on cell type)
- is the period where cells are “overtly” dividing
- all other activities are put on hold. This is because the “normal” internal organisation of the cell is disrupted in this stage.
describe the interphase
Consists of:
- Gap 1 (G1) - normal cell metabolism
- s: when DNA replication occurs
- Gap 2 (G2) - preparation for cell division
- most cells spend most of their time in this phase. it may last for hours, days, weeks or longer.
- during this phase, cells grow to their mature size.
- interphase cells are metabolically active. E.g., glucose oxidation, synthesis of macromolecules
what happens in Pre-mitosis? (interphase G2 phase)
in the G2 phase, the cell is preparing to enter mitosis:
- DNA has been duplicated in the previous S phase
- duplicated DNA still in the form of chromatin
what happens in Mitosis 1: prophase?
- DNA condenses from chromatin into X-shaped chromosomes
- centrosome divides and along with microtubules, form the mitotic spindle.
what happens in mitosis 2: prometaphase?
- kinetochores are protein structures on chromosomes that bind to microtubules
- chromosomes are anchored to the mitotic spindle via kinetochores
what happens in mitosis 3: metaphase?
- the mitotic spindle moves the chromosomes to the middle of the cell
- cystoskeletal elements are used as well, one type to elongate and push apart the cell, the other to contract and pull the chromatids apart
what happens in mitosis 4: ANAPHASE?
- microtubules pull sister chromatids apart
- as the microtubules contract, the chromatids are pulled into opposite ends of the cell.
