Cell replication Flashcards
What are the proteins involved in the formation of cytoskeleton elements?
Actin filaments
Intermediate filaments
and microtubules (tubulins)
What are the roles of an intracellular cytoskeleton?
Maintains cell shape and structure Transportation of organelles Cellular division (kinetochore fibers and spindle contraction)
What proteins comprise microtubules?
Alpha and beta tubulins
How are tubulins arranged in microtubules?
Helical configuration
Why is the helical configuration important in microtubules?
Enables the expansion and development of microtubules, additional tubules can be added or subsequently removed
Where do microtubules originate from?
Microtubules originate from the microtubule organising centres
What major protein comprises microfilaments?
Actin
What are the functions of microfilaments?
Proteins assist with the motility of organelles and cell
How are cilia and flagella arranged?
9 + 2 configuration
How do microtubules assist with the movement of organelles?
Microtubules are associated with motor proteins
What is aneuploidy?
An abnormal number of chromosomes
In cancer cells, how is cell division unregulated?
Contact inhibition of growth does not occur, as tumor cells do not recognize adjacent cells thereby resulting in the continued proliferation of cancer cells
What are the stages of the cell cycle?
Interphase, mitosis, cytokinesis
What are examples of nuclear division?
Mitosis and meiosis
What is cell division?
Cell division involves the separation of cytoplasmic contents (cytokinesis) M phase
What is G1?
The chromosomes form long uncondensed threads wound onto histone, cell is metabolically active.
Protein synthesis occurs
Organelle production
Cytoplasmic volume increases
What is the structure of the chromosome within the G-phase?
The chromosomes present are uncondensed
Which proteins are associated with chromosomes?
Histone proteins
What occurs during the S-phase?
S phase is referred to as the synthesis phase whereby semi-conservative replication occurs within the nucleus/.
Histones are synthesised and attached to DNA
organelle synthesis: Mitochondria, centromere, golgi apparatus
How are chromosomes structured within the S-phase?
Chromosomes are condensed and visible as sister chromatids attached to the centromere
When is replicated DNA checked for errors and corrected?
G2 phase
Which phase during the cell cycle in which spindle proteins are produced?
G2 phase
What is M-phase?
Mitosis (nuclear division) and cytokinesis
When is mitosis most vulnerable?
Irradiation, heat shock chemicals
DNA Damage cannot be repaired
Gene transcription silenced
When is the decision point?
G1
When is the second decision point?
G2
What is the structure of centrioles?
Small hollow cylinders made of microtubules, made from the globular protein tubulin
Describe how centrioles arranged?
pairs at right angles to each other, forming a centrosome
Composed of 9 triplets of microtubules
What is a centrosome?
Mother and daughter centriole pair
What is the function of a centriole?
Involved in the separation of chromosomes during cell division; producing a spindle
Which centriole do microtubules project from?
Elongate from mother centriole
What is chromatin?
The complex of DNA & Protein
What are the stages of mitosis?
Prophase
Metaphase
Anaphase
Telophase
What occurs during prophase 1?
Chromosome condensation occurs, chromosomes become visible as sister chromatids attached by the centromere and associated with kinetochore fibres
What occurs during prophase II?
Spindle formation, duplicated centrosomes migrate to opposite poles of the nucleus, organize
Assembly of spindle microtubules
Asters form, radial microtubule array
Where do the radial arrays meet?
The radial arrays form a collection of polar microtubules at the spindle equator, collectively forming the spindle
What state are microtubules in?
Dynamic state
What is a dynamic state?
Constant arrangement and addition of tubulin molecules (polymerization and depolymerisation)
What occurs during prometaphase-I?
Nuclear envelope breaks down, releasing chromatids into the cytoplasm
Nucleolus disappears,
Spindle formation mainly complete
What is the role of kinetochore fibers?
Project from the centromere, interact with spindle microtubules, attachment of chromosomes to the spindle
What occurs during metaphase?
Microtubules from the opposite pole is captured by sister kinetochore.
Contraction of spindle cause chromosomes to translocate towards the centre (spindle equator)
What is CENP-E?
Centromere protein E (Kinetochore tension sensing)
What occurs during anaphase?
Centromeres split, separating each sister chromatid
Spindle contracts, pulling the chromatids centromere first towards the opposite pole
Movement of chromatids caused by overlapping spindle fibres sliding past each other
Spindle fibres lengthen and shorten depending on addition/removal of tubulin molecules
ATP is used
What protein holds the sister chromatids together, and is subsequently broken down during anaphase?
Cohesin
What occurs during Anaphase-A?
Breakdown of cohesin, microtubules get shorter, and daughter chromosomes pulled towards opposite spindle poles
What occurs during Anaphase-B?
Daughter chromosomes migrate to poles, spindle poles migrate apart
What process occurs during telophase?
New nuclear envelope develops around the group of chromatids
Formation fo two identical daughter nuclei
Chromatids uncoil and lengthen into chromosomes
Spindle fibers disintegrate, and formation of the nucleolus
A contractile ring of actin and myosin filaments assembled
What happens to the chromatids during telophase?
Uncoil and lengthen, nucleolus reforms
What proceeds from telophase?
Cytokinesis occurs, division of cytoplasm
What forms at the equator of the cell during cytokinesis?
Cleavage furrow
How does the cleavage furrow split the cells into two?
Contractile ring
What are spindle assembly checkpoints?
Monitors the status of chromosome microtubule attachments, delays the onset of anaphase until the kinetochores have formed stable bipolar connections with the mitotic spindle
How do kinetochore fibres attach to the mitotic spindle?
Form stable bipolar connections
What protein comprises kinetochore fibres?
Centromere protein E (CENP-E)
BUB protein kinases bind onto kinetochore and dissociate once chromosomes are properly attached
Which kinases detects the correct attachment of chromatids to spindles?
BUB protein kinases
What is aneuploidy?
The mis-attachment of microtubules to kinetochore fibres resulting in abnormal number of chromosomes
Why does aneuploidy occur?
Defects in the mitotic spindle checkpoint facilitate tumorigenesis
Why does aberrant division occur?
Multipolar spindles, defects in chromosome cohesion, spindle attachment defects
Impairment in spindle checkpoint
What is a cell-cycle arrest?
Stopping point within the cell cycle no longer involved in duplication or replication
Cell cycle checkpoints are control mechanisms that regulate proper cellular division
Including DNA damage and insufficient cell size
What is apoptosis?
Programmed cell death
What enzymes initiate
Initiator caspases
What phase do cells enter due to the absence of stimulus?
Quiescent phase
Which phase are differentiated phase predominantly in?
G0
What is the signaling cascade initial step?
Extracellular growth factor ligand binds to GF receptor,
What occurs after growth factor ligand binding to GF receptor?
Receptors pair up and behave as kinases, phosphate groups to intracellular molecules. Kinases RAF is activated
RAF phosphorylates and activates MEK
MEK phosphorylates ERKs
What is MEK?
Mitogen activated protein kinase
What are ERKs?
Extracellular regulated kinases
What do ERKs do?
Phosphorylate and activate variety of target molecules, transcription factors (C-myc)
What is C-myc?
Transcription factor
What is the RAF-MEK-ERK pathway?
Mitogen activated protein kinase cascade
What is a mitogen?
The signal that causes a cell to undergo mitosis or divide
Promotes the transition of G0 to G1
What is a CDK?
A cyclin-dependent kinase
What are CDKs?
Responsible for regulating the cell cycle, involved in regulating transcription, mRNA processing and nerve cell differentiation
What Cyclin gives direction and timing to the cycle?
Cyclin-E