Rachael Curry Flashcards
Fundamental properties of cells
= small to facilitate diffusion of molecules etc. in / out
= self-propagating (death due to age/disease/program), keeps size consistent
=packages maintained by membrane. Proteins on the membrane determine cell function (how cells interact w/environment)
Basic features of a prokaryotic cell
small(er than eukaryotic)
no internal membranes
nucleoid region
eg- bacteria
Basic features of a eukaryotic cell
large(r than prokaryotic)
contains membrane-bound organelles
nucleus
eg- animal cell
What differentiates a prokaryotic cell from a eukaryotic cell?
size / organisation of genes / internal structure
Organelles function as part of a. . .
system!!
Protein expression in prokaryotes
DNA –transcription–> mRNA –translation–> protein
DNA not enclosed
Protein expression in eukaryotes
DNA –transcription–> mRNA –translation–> protein
DNA packaged and enclosed in double-membraned nuclear envelope, therefore nuclear pores exist to allow communication between nuclear and cytosolic compartments.
Function of ribosomes
Decode mRNA by converting the sequence of bases into a linear polypeptide of amino acids
DNA packaging
Negatively-charged DNA packaged with positively-charged histone proteins to form a CHROMATIN complex.
1) heterochromatin (densely-packed as mostly INACTIVE genes, found on periphery of nucleus)
2) euchromatin (less dense as more ACTIVE genes are found here, found in centre of nucleus)
Both chromatin complexes surrounded by nucleoplasm.
Nucleolus =
Site of ribosome synthesis.
Large nucleolus = active ribosome synthesis = cell requires many proteins to be produced
Ribosome + Endoplasmic Reticulum =
Rough Endoplasmic Reticulum
Why do ribosomes bind to ER?
Translates a sequence of mRNA bases that act as a SIGNAL, shepherded to ER rather than cytosol.
Binds to ER, making RER.
Once finished translation, injects protein into the lumen of the RER and remains attached.
Secretion pathways
RER lumen = site of most membrane synthesis
synthesis in RER —carried by vesicles—> modification in Golgi apparatus —carried by vesicles—> delivery via secretion / plasma membrane
role of RER =
to secrete proteins into the cytoplasm
(among its functions is the production of proteins and steroids, the maintenance of plasma membranes, and a pathway for molecules to move along)
role of Golgi =
to process and bundle macromolecules, eg- proteins and lipids, as they are synthesized within the cell.
role of vesicles =
carry contents (cargo) from one organelle to another
VESICLES = CONSEQUENCES OF COMPARTMENTALISATION OF CELLS
regulated vs. constitutive secretion
regulated = signal required to trigger the release of cargo from the Golgi to the membrane
constitutive = no signal required (continuous process)
Plasma membrane structure variations
most membranes = 50% lipid, 50% protein
BUT that balance can change depending on the type of cell
eg (1)- myelin = insulator of axons
therefore, membrane = 80% lipid (non-conductive), 20% proteins
eg (2)- inner mitochondrial membrane = 25% lipid, 75% protein
How do vesicles move through cytoplasm?
along a microtubule track, powered by a motor protein
microtubules extend from cell centre (centrosome)
close to centre = -ve
far from centre = +ve
Easy movement of vesicles from +ve to -ve
Uptake and Degradation
refers to cell processes allowing the breakdown of own old/damaged components or foreign bodies, and the uptake of nutrients etc.
endocytosis =
endocytosis is a cellular process in which substances are brought into the cell. the material to be internalized is surrounded by an area of plasma membrane, which then buds off inside the cell to form a vesicle containing the ingested material.
material sorted - some is destroyed in lysosomes (low pH/contain hydrolytic enzymes) and some is recycled back to the cell surface
autophagy =
the regulated mechanism of the cell that disassembles unnecessary or dysfunctional components. these components are then digested by lysosomes.
frees up cell components during starvation to benefit cell and organism
Some cells contain lysosomes. Function = ?
A lysosome is a membrane-bound organelle. they are spherical vesicles that contain hydrolytic enzymes that can break down many kinds of biomolecules. The lumen’s pH (4.5–5.0) is optimal for the enzymes involved in hydrolysis. the lysosome is involved in various cell processes, including secretion, plasma membrane repair, cell signalling, and energy metabolism.
phagocytosis =
type of endocytosis
the ingestion of bacteria or other foreign material by phagocytes (a type of cell within the body capable of engulfing and absorbing bacteria and other small cells and particles)
pinocytosis =
type of endocytosis
small particles suspended in extracellular fluid are brought into the cell through an invagination of the cell membrane, resulting in a suspension of the particles within a small vesicle inside the cell. these pinocytotic vesicles subsequently fuse with lysosomes to hydrolyse the particles. This process requires energy in the form of ATP
receptor-mediated endocytosis =
a process by which cells absorb metabolites, hormones, proteins, and viruses by the inward budding of the plasma membrane. this process forms vesicles containing the absorbed substances and is strictly mediated by receptors on the surface of the cell. only the receptor-specific substances can enter the cell through this process.
Uptake and degradation in CYTOSOL targets. . .
usually aged/misfolded proteins (cell notified by Golgi)
Tagged with ubiquitin and then degraded by proteosomes
Cytoskeleton components =
microfilaments microtubules intermediate filaments centrosome centrioles
microfilaments =
generate contractile forces (movement)
7 nm thick
subunits = myosin and actin
microtubules =
part of dynamic framework of cell - position organelles
25 nm thick
subunits = tubulin
intermediate filaments =
provide strength and support (NOT dynamic)
10 nm thick
subunits = keratins and lamins OR vimentin and desmin (depends on tissue)
centrosome =
organelle that serves as the main microtubule organizing centre of the cell as well as a regulator of cell-cycle progression.
a bound pair of centrioles, surrounded by a shapeless mass of dense material, called the pericentriolar material, makes up a structure called a centrosome.
centrioles =
function as the microtubule organizing centre
it is an important event in major cellular process, eg- cell division. the centrioles pair duplicates within a cell and the two pairs migrate to the opposite ends of the cell to organize the mitotic spindle.
Smooth ER =
domain of ER membrane without ribosomes
Functions of smooth ER =
It makes up proteins and lipids that get exported by the cell, eg- steroid and lipid production.
The smooth ER also controls the level in the muscles and detoxifies poisons, alcohol, and
drugs.
Peroxisomes =
type of organelle known as a microbody, found in virtually all eukaryotic cells.
Functions of peroxisomes =
A major function of the peroxisome is the breakdown of very long chain fatty acids through beta-oxidation.
Generates H2O2 (excess broken with catalase to O2 and H2O)
Stages of cell division
prophase
metaphase
anaphase
telophase
Causes of cell death
by apoptosis (programmed cell death)
by damage
by disease
What specialises a cell?
protein expression defines the type of cell and its function
4 basic tissue types =
epithelia
connective
muscle
nervous
Classes of stem cells and their locations
Totipotent = can produce all cell types, found in embryo Pluripotent = can produce many unrelated cell types, found in blastocyst Adult = can produce tissue-specific cells for regenerative purposes, found in body tissue (eg- bone marrow)
How do cells communicate?
by releasing chemicals / proteins from one cell, which are received by another cell with the correct receptor
endocrine comm.
hormones transported through bloodstream (slowest-acting)
neuronal comm.
neurotransmitters transported across synapses (faster than endo/paracrine, slower than contact-dependent)
paracrine comm.
signal cell –> mediator cell –> target cell (faster than endocrine, slower than neuronal and contact-dependent)
contact-dependent comm.
membrane-bound signalling molecule (fastest-acting)
Cell-cell selective adhesion
static cells can adhere to each other to create a range of junctions to allow communication AND transfer of chemicals
3 types of junction
TIGHT = prevent movement of substances between cells ANCHORING = keeps cells together in their relative positions and plays an important role in the structural cohesion of tissues GAP = allow movement of substances between cells
