FOUNDATION-CELLS Flashcards
Which phases make up interphase?
G0
G1
S
G2
What happens in G0 phase?
rest phase
what happens in G1 phase?
organelles duplicated
what happens in S phase?
DNA synthesis-each of 46 chromosomes is duplicated by the cell
what happens in G2 phase?
cell growth and prep for mitosis -cell double checks the duplicated chromosomes for error-makes needed repairs
what do checkpoints do?
- points in a eukaryotic cell cycle in which it examines the internal and external conditions and determines whether to continue with the cycle
- they can halt the cell cycles and promote apoptosis in some circumstances to protect the cell from DNA damage
what do defects in checkpoints lead to?
aneuploidy
polyploidy
what are examples of important checkpoints?
G1-commit to cell division-site of action of p53 (tumour suppressor gene)
G2-ensure DNA fidelity
spindle-ensures that chromatids are attached to tubules correctly
what is DNA fidelity?
the ability of DNA polymerase to accurately synthesise a new strand from the template strand
what is p53 and what does it do?
tumour suppressor gene-a protein that regulates cells from growing and proliferating too fast
what are cyclins?
proteins that control the progression of a cell through the cell cycle by activating CDKs
what are CDKs?
- cyclin dependent kinases
- bind to cyclins to be activated
which cyclins are present at which stage in the cell cycle?
- G1-S transition=cyclin D
- S-Cyclin E
- G2-M transition=cyclin A
- Mitosis=cyclin B
what are the 4 different types of cell death?
- apoptosis
- necrosis
- anoikis
- autophagy
describe apoptosis.
- programmed, controlled cell death
- extrinsic and intrinsic
- involves FAS/TRAIL (ligands) binding to death receptors on the cell surface + involves caspases (proteases)
- no inflammatory response
describe necrosis.
- cell death due to acute cellular injury
- not regulated
- always pathalogical eg infectious agents (bacteria/ virus/ fungi), o2 deprivation, heat, radiation
- initiates an inflammatory response
describe anoikis.
- controlled cell death in anchorage-dependent cells (eg epithelial cells)
- due to loss of cell extracellular matrix interaction
- no inflammatory response
- loss of anoikis can contribute to cancer metastasis
describe autophagy.
- degradation and recycling of cellular components-may or may not lead to cell death
- involves formation of an autophagosome that encapsulates cytoplasm, malformed proteins, organelles, or pathogens and then fuses with lysosome for degradation
what is mitosis and its purpose?
- 1 cell divides into 2 genetically identical daughter cells
- in the various stages the cells chromosomes are copied and then distributed equally between 2 nuclei of daughter cells
- purpose=growth and repair
what happens in prophase?
- chromosomes condense
- nuclear envelope disappears
- spindles form
what happens in metaphase?
- sister chromatids line up at equator
- spindles attach to centromere
what happens in anaphase?
- spindles contract
- sister chromatids are pulled apart to opposite poles of cell
what happens in telophase?
- mitotic spindle breaks down
- nuclear envelope reforms around chromosomes
- chromosomes begin to decondense and return to stringy form (chromatin)
what occurs after telophase?
cytokinesis-cytoplasm splits in 2 and cell divides
what is meiosis?
-1 diploid cell (2n) undergoes 2 rounds of division but only 1 round of DNA replication
what does meiosis result in?
4 haploid (n) daughter cells
how do the cells produced in meiosis have genetic variation?
- independent assortment of chromosomes in metaphase 1
- chiasmata (recombination)-allele shuffling in prophase 1
what are stem cells?
undifferentiated cells which have the ability to specialise into cells of different lineages/potency
what does totipotent mean?
can differentiate into any cell type-embryonic & extraembryonic (zygote/ blastomeres)
what are pluripotent cells?
-can develop into cells of any of the 3 germ layers (inner cell mass of blastocyte that give rise to the embryonic stem cells ESCs)
what are multipotent cells?
can develop into several different cell types (haematopoietic and epithelial stem cells)
what are the types of membrane transport?
- endocytosis
- exocytosis
- pinocytosis
- phagocytosis
describe endocytosis
- brings substances into cell
- membrane forms a vesicle around cell
- uses atp
describe exocytosis
- expels vesicles from cell
- cytoplasmic secretory vesicles fuse with cellular membrane-release contents into extracellular space
describe pinocytosis.
-process by which liquid droplets are ingested by living cells
describe phagocytosis.
uptake of solid particles by a cell
what is simple diffusion?
- movement of non-polar compounds only
- down concentration gradient
- passive
what is facilitated diffusion?
- diffusion down electrochemical gradient
- with help from channel/carrier proteins
what is primary active transport?
- diffusion against electrochemical gradient
- driven by ATP
what is secondary active transport?
- diffusion against electrochemical gradient
- driven by ion moving down its gradient
how does transport occur by ion channels?
down electrochemical gradient
may be gated by a ligand or ion
how does ionophore-mediated ion transport?
down electrochemical gradient
what are the different types of cell junctions?
- tight junctions
- gap junctions
- adherens junctions
describe gap junctions.
- allow movement of substances between cells
- formed by 6 connexin proteins (in membrane of each cell)
- 2 connexins aligned together forms a channel between 2 cells
- passage for excitatory signals eg muscle and cardiac cells
describe tight junctions.
- stops movement of substances between cells
- contains interlocking junctional proteins which join adjacent cells
what do adherens junctions do?
maintain cell position
what are the 3 types of transporter proteins?
- uniporter- single substance moves in a single direction
- symporter- 2 substances move in the same direction
- antiporter- 2 substances move in opposite direction
what are 2 types of receptors?
- tyrosine kinase receptors
- G-protein coupled receptors (super family)
what is a kinase?
an enzyme which phosphorylates molecules
what are tyrosine kinase receptors formed by?
amino acid tyrosine
how do tyrosine receptors work?
- when ligands bind to receptors the tyrosine polypeptide join together to form a dimer (the ligand activates the tyrosine regions to phosphorlyate each other)
- relay proteins bind to the complex and initiate its own cellular response eg insulin
- it acts as a ligand and the cellular response will lead to GLUT 4 channels being taken to the cell surface membrane to allow movement of glucose into cells
which GPCR receptors are targets of many catecholamines (adrenaline/ noradrenaline)?
adrenergic receptors
what do molecules do to GPCR receptors?
molecules bind to these receptors and activate an internal signal transduction pathway to eventually create a cellular response
what does the structure of GPCR consist of?
- 7 alpha helices joined by 3 intracellular and extracellular loops
- arranged in barrel like structure
what does a G protein itself consist of?
- an alpha, beta and gamma subunit
- GDP (guanosine diphosphate) when inactive
what does GDP turn into when activated?
GTP
how are G proteins activated?
- extracellular ligan binds to receptor
- creates conformational change in tertiary structure of receptor-causes interaction between receptor and G protein
- GDP is substituted by GTP
what happens after GDP is substituted by GTP?
- G-protein dissociates
- the alpha-GTP complex can bind with and activate effector enzymes eg ADENYL CYCLASE/ phospholipase C
- beta-gamma complex mainly binds with and activates ion channels and kinases
- the activated alpha-subunits stimulates adenyl-cylclase to convert ATP to cAMP (secondary messenger)
what does secondary messenger cAMP activate?
-protein kinase A
what does protein kinase A do?
phosphorylates enzymes and proteins (activating them)
eg in sympathetic response-pkA stimulates many glycogen -degrading enzymes in the liver tissue
what do protein molecules -arrestins do?
can bind to G protein receptors and prevent it from binding in G proteins
what is polyploidy?
possessing more than 2 complete sets of chromosomes
what is aneuploidy?
possessing an abnormal number of chromosomes (eg missing one or having one extra-trisomy)
how do CDKs become activated?
-cyclins bind to CDKs and are phosphorlyated for them to be activated
what is extrinsic apoptosis triggered by?
- apoptosis triggered by signals from outside the cell
- FAS/ TRAIL ligands binding to death receptors
what is intrinsic apoptosis triggered by?
apoptosis triggered by stress or damage to cell
which cell death type causes an inflammatory response?
necrosis
occasionally autophagy
which cell deaths are controlled?
apoptosis
anoikis
autophagy
