cell biology and cell interactions Flashcards
plasma membrane:
the plasma membrane is a semipermeable barrier.
controls traffic between cell and external environment.
regulation of traffic by transmembrane proteins.
channels, carriers, pumps.
the nucleus:
Nuclear envelope– Porous double membrane separating the nucleus from
the cytoplasm.
– Continuous with lumen of endoplasmic reticulum.
– Inner membrane is
supported by protein layer called the nuclear lamina.
Nuclear pores– Facilitate and regulate
exchange of materials such as proteins and RNA between nucleus and cytoplasm.
chromatin is surrounded by nucleoplasm.
The Nucleus: Storage of Genetic Information:
Histones are proteins that aid folding of DNA in chromosomes to tightly pack it.
Chromatin is complex of histones and DNA that make up the chromosomes inside the nucleus.
chromatin:
2 classes:
Heterochromatin-
Tightly condensed
throughout the cell cycle.
Generally inactive in
transcription.
Euchromatin-
Less condensed.
Contains actively
transcribed genes.
the nucleolus:
membraneless part of nucleus.
involved in production and assembly of ribosomes. assembles ribosomes from >50 different proteins and 3 RNA molecules.
the cytoskeleton:
a cellular scaffolding or skeleton contained within the cytoplasm in all cells.
dynamic structure
eukaryotic cytoskeleton:
3 types of filaments: microfilaments (actin), intermediate filaments, microtubules.
microfilaments (actin):
microfilaments are most concentrated just beneath the cell membrane.
composed of 2 intertwined actin chains.
functions of microfilaments:
responsible for resisting tension (stress fibres), maintaining cellular shape, participation in some cell to cell or cell to matrix junctions.
are essential to signal transduction.
are important for cytokinesis, muscular contraction (with myosin), cytoplasmic streaming (with myosin), reorganisation of cytoplasm.
intermediate filaments:
more stable (strongly bound) than actin filaments.
heterogeneous constituents of the cytoskeleton.
throughout the cell.
functions of intermediate filaments:
like actin filaments, they function in the maintenance of cell shape by bearing tension.
organise the internal 3D structure of the cell.
anchor organelles.
structural components of the nuclear lamina.
also participate in some cell-cell and cell-matrix junctions.
components of intermediate filaments:
different intermediate filaments are: made of vimentins, being the common structural support of many cells.
made of keratin, found in skin cells, hair and nails.
neurofilaments of neural cells.
made of lamin, giving structural support to the nuclear envelope.
microtubules:
made of alpha and beta tubulin.
have a very dynamic behaviour. constantly elongated and shortened.
form ring and nucleus. radiate out from this ring.
resist compression compared with other cytoskeletal filaments.
microtubule structure:
made of protofilaments.
polymers of alpha and beta tubulin dimers. bundle in hollow cylindrical filaments- 25nm in diameter. lumen is approx 15nm in diameter.
arranged in an imperfect helix. 1 turn of the helix contains 13 tubulin dimers each from a different protofilament.
have polarity (alpha tubulin at 1 end and beta tubulin at other).
functions of microtubules:
they play key roles in: intracellular transport (they transport organelles like mitochondria or vesicles), the cytoskeleton (axoneme) of cilia and flagella, synthesis of the cell wall in plants, the mitotic spindle.
microtubules form centrioles:
centrioles: in 9 triplet sets (star shaped). involved in the organisation of the mitotic spindle and in the completion of cytokinesis.
position determines the position of the nucleus and plays a crucial role in the spatial arrangement of cell organelles.
microtubules form cilia and flagella:
cilia and flagella: microtubules are in 9 doublets orientated about 2 additional microtubules (wheel shaped).
as both are structural components of the cell, and are maintained by microtubules, they can be considered part of the cytoskeleton.
ATP synthase:
an enzyme that synthesises ATP from ADP and inorganic phosphate (Pi).
ATP synthesis uses energy. protons (H+) moving down an electrochemical gradient from the intermembrane space into the matrix.
organelles:
microvilli: extensive folding of the cell membrane, increase surface area for absorption.
cell membrane: bilayer of phospholipid molecules with inserted proteins, acts as a gateway for and barrier to movement of material between the interior of the cell and extracellular fluid.
cytosol: semi gelatinous substance, contains dissolved nutrients, ions, wastes, insoluble inclusions, suspends the organelles.
centrioles: bundles of microtubules, direct movement of DNA during cell division.
lysosomes and peroxisomes: membrane bound vesicles filled with enzymes, digest bacteria, old organelles, metabolise fatty acids.
mitochondrion: double wall with central matrix, produces most of the cells ATP.
golgi complex: hollow membranous sacs. modify and package proteins.
organelles 2:
nucleus: central lumen with a 2 membrane outer envelope with pores, contains DNA to direct all functions of the cell.
nucleolus: region of DNA, RNA and protein, contains the genes that direct synthesis of ribosomal RNA.
rough endoplasmic reticulum: membrane tubules that are continuous with the outer nuclear membrane, edged with ribosomes, site of protein synthesis.
smooth endoplasmic reticulum: same as rough ER without ribosomes, synthesises fatty acids, steroids and lipids.
ribosomes: granules of RNA and protein, assemble amino acids into proteins.
microtubules and microfilaments: protein fibre, provide strength and support, enable cell motility and transport.
microvilli:
microvilli increase cell surface area. they are supported by microfilaments.
microfilaments form a network just inside the cell membrane.
microtubules are the largest cytoskeleton fibre.
intermediate filaments include myosin and keratin.
peroxisomes:
contains organelles, enclosed in membrane.
contains over 50 enzymes for variety of metabolic reactions.
does not have its own DNA but replicate by division.
oxidising reactions with end product hydrogen peroxide, inactivated by catalase.
fatty acids, amino acids, uric acids are all broken down here.
lysosomes:
like peroxisomes these have a membrane.
break down nucleic acids, carbohydrates, proteins and lipids. recycling centre.
can have lots of variation in size shape.
approx 50 degradative enzymes, mutations in these genes lead to more than 30 different genetic diseases. lysosome storage diseases.
gap junctions:
can respond very quickly to bacterial pathogens.
limit the spread of toxicity in a tissue. also after chemical damage or radiation damage.
gap junction protein expression alterations linked to many diseases or pathophysiological conditions.
cannabinoids linked to inhibition of gap junction intercellular communication.
