eukaryote cell Flashcards
Evolution of cell
cells evolved to be able to compartmentalise their cell organelles-this became eukaryotes
eg: animal, plant, fungi, protoctista
Compartmentalisation of the cell allows all the enzymes and compounds necessary for a process to be localised and concentrated
Eukaryotic cell sub-divide specific tasks into membrane bound organelle
Need for an active and organised transport systems through the cell
Compartmentalisation allows cells to differentiate and specialise into specific functions
This becomes increasingly important in multicellular organisms with dedicated structures/organs for performing specific functions
The nucleus: Nuclear Structure Nuclear Import/Export The nucleolus
Double membrane (nuclear envelope) bound compartment containing the genetic information of the cell
Genetic information: organised into chromosomes
nucleoleus:
The site of ribosomal RNA production
Responsible for synthesising and assembling RNA and protein: to form ribosomes-essential for protein synthesis
Dedicated organelle for ribosome production, one or more spherical structures, several micrometers in diameter
nuclear envelope:
separates nucleus from cytoplasm
comprised of two membranes:
Inner nuclear membrane
Perinuclear space (20-40nm)
Outer nuclear membrane ->continuous with the ER
nuclear pores(transport of molecules):
Simple diffusion of small molecules
* Small particles injected into cells can directly enter the nucleus.
* Cut-off point is a Molecular weight of around 30.000 dalton, corresponding to a diameter of 9 nm.
* Proteins particles above this can not passively enter the nucleus.
* Channels are freely permeable to ions and small molecules
* This enables nucleoside triphosphates (dNTPs) and other small molecules needed for metabolism to diffuse freely.
Proteins can be transported from the cytoplasm into the nucleus contain:
Nuclear Localisation Signal (NLS), a specific amino acid sequence.
The NLS signal is recognised by a receptor protein called Importin.
Importin binds NLS containing proteins and regulates transport through the nuclear pore.
RNA molecules, synthesised in the nucleus, but function in the cytoplasm:
RNA transported from the nucleus into the cytosol bind proteins that contain a Nuclear Export Signal (NES).
The NES signal is recognised by a receptor protein called Exportin.
Exportin binds NES containing proteins, transports them, and their associated RNA through the nuclear pore. Protein/RNA complexes: size limitation for import/export is around 26nm.
nuclear matrix:
Nuclear matrix maintains the shape of the nucleus (a scaffold).
Comprises of an insoluble fibrous network of proteins.
Newly synthesised nucleic acids associate with the matrix.
lamina:
Thin, dense network of fibres that line the inner nuclear membrane.
10-40 nm thick, constructed of proteins called Lamins.
Gives the nucleus mechanical strength within the cell.
The endoplasmic reticulum (ER) The rough ER The smooth ER The Transitional ER
Interconnected cisterns+tubular membranes
Rough ER: ribosomes decorated-to make secretory proteins
Transitional ER: lipid and protein transport
Smooth ER: lipid synthesis, calcium storage, detoxification
smooth ER:
Drug detoxification
Carbohydrate metabolism: hepatocytes-breakdown of stored glycogen
Calcium storage: sarcoplasmic reticulum in muscle cells (specialised smooth ER), electrical pulses
Stored calcium is released in response to extra cellular signalling to allow muscle contraction
Steroid biosynthesis:
Adrenal glands, testes, ovaries
Cholesterol and steroid based hormones
transitional ER:
TER: the exit site of proteins leaving the rough ER
corresponds to small patches of proteins decorating the ER throughout the cell
The Golgi
Stack of flattened membranes
2primary functions:
protein processing and organise further transport
Major sorting compartmentn for protein traffic within the cell
Along the secretory and endocytic pathway
one side cis, one side trans
Medial
Processing of cargo proteins
Trimming of sugars and phosphorylation
Attachment of sugars-initial phosphorylations
Attachment of sulphates
Transport vesicles, endomembrane, lysosomes
Membrane bound small packages
Contain proteins for export in between ER, Golgi, plasma membrane and out
Anterograde transport
Retrograde transport
Endocytosis imports extra cellular material by forming vesicles from the plasma membrane
Mitochondria
Site of aerobic respiration
Contains inner and outer membrane
Cells performing high energy tasks contain many mitochondria
outer membrane:
Not a significant permeability barrier
Transmembrane channel proteins: porins
inter membrane space:
Because of all the porins the inter membrane space is the same as the cytosol with respect to small molecules
Specific proteins can be targeted to this space
inner membrane:
Permeability barrier to most solutes
Partitions the mitochondria in 2 components
inner membrane cristae:
Used to greatly increase the surface area
SA: inner: outer (membrane)
5:1
Can accommodate large numbers of protein complexes
Number of mitochondria in a cell
Number of cristae ~activity of the cell
matrix:
Contains enzymes, DNA and ribosomes
Mitochondria DNA encodes:
Ribosomal RNAs
Transfer RNAs
Inner membrane proteins
Membrane trafficking
Secretion through exocytosis
Phagocytosis-cell eating
Pinocytosis-cell drinking
Receptor meditated endocytosis
Newly discovered pathway->exosomes=>extracellular vesicles
Invagination-inside the cell
like a double endocytosis
this is to get rid of malfunctioning organelles in a cell
multivesicular endomembranes
Either leave cell
Plants-go to cell wall
Animals-extra cellular
Includes rna, proteins
Endocytosis
Come together to form early endosome
Becomes late endosomes/sorting endosomes
Endocytic vesicles never goes straight to late endosome
Decision occurs to either be used as recycling or degradation
Recycling involves fusion compartments, transport vesicles or PM
lysosomes
Storage for enzymes used to break up cellular components (upon autophagy)
Contain 50+ hydrolytic enzymes
Capable of breaking down almost any biological compound so must be separated from rest of cell
Vary in size
Highly mobile
Peroxisomes
subset of small vesicles
Assist lysosome in cells clean up work
Generate and degrade hydrogen peroxide
Breakdown fatty acids/lipid components of membranes
Detoxify harmful compounds
Move locally, not very mobile
Cytoskeleton
Microtubules and actin
Framework for cell size, shape and structure
Forms the basis of transport systems in a cell
Centrosomes(animals only)
Contain 2 barrell-shaped centrioles 0.2microns in diameter
Microtubules of the cytoskeleton are nucleated from the centrosome
Filaments/actin
Influence locomotion and movement
Major cytoskeleton component of muscle cells
The formation of lamellipodia during cell movement is based on the constant assembly /disassembly of actin filaments
plasma membrane
Defines cell boundaries and retain cell content
Lipid bilateral containing “proteins”
