Lecture 6: Cell biology and cell interactions Flashcards
Plant cells
> Have cell wall (cellulose and lignin) and cell membrane
Have large vacuoles (90% of cell volume)
Regular shape (10-100um)
Have chloroplast for photosynthesis
Centrioles present only in cells of lower plant forms
Contain glyoxysomes to convert fatty acids to carbohydrates
Contain amyloplasts (Contain starch)
Animal cells
> Have cell membrane only
May have several small vacuoles
Irregular shape (10-30um)
No chloroplasts
Centrioles always present
No glyoxysomes present
No amyloplasts present
The plasma membrane is the semipermeable membrane
> Controls traffic between cell and external environment
Regulation of traffic by transmembrane protein
-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
-Facilitates and regulate
exchange of materials such
as proteins and RNA
between nucleus and
cytoplasm
Histone 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: Heterochromatin
–>Tightly condensed throughout the cell cycle
–>Generally inactive in transcription
Chromatin: Euchromatin
–>Less condensed
–>Contain actively transcribed genes
The nucleolus
> Membrane 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
Functions
Eukaryotic cytoskeleton
> 3 types of filaments:
-Microfilaments (actin)
-Intermediate filaments
-Microtubules
Microfilaments- actin
> Microfilaments are most concentrated just beneath the cell membrane
Composed of two intertwined actin chains
Functions of microfilaments
> Are 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
-Cytoplasmic streaming
Intermediate filaments
> More stable (strongly bound) than actin filaments
Heterogeneous constituents of the cytoskeleton
Throughout the cell
Functions of intermediate filaments
> Like actin filaments, the function in the maintenance of cell-shaped 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
Like actin filaments, they function in the maintenance of cell-shape by bearing tension
Organise the internal 3D structure of the cell
Composition 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 around nucleus
-Radiate out from this ring
Resist compression compared with other cytoskeletal filaments
Microtubules structure
> Made of protofilaments:
-Polymers of alpha and
beta tubulin dimers
-Bundle in hollow
cylindrical filament –>
25nm in diameter
–>Lumen is approximately
15nm in diameter
-Arranged in an imperfect
helix
–>One turn of the helix
contains 13 tubulin
dimers each from a
different protofilament
-Have polarity (alpha
tubulin at one 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 from 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 oriented about
two additional
microtubules (wheel-
shaped)
-As both are structural
components of the cells,
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 inter-membrane
space into the matrix
ATP synthase is located in the inner membrane of the mitochondrion
Peroxisomes
> Some 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, inactive 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 and shape
Approximately 50 degradative enzymes, mutations in these genes leads to more than 30 different genetic disease
-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
