Organisation Of Eukaryotic Cells Flashcards
In which eukaryotic kingdom do all cells lack rigid cell walls?
All cells in the animal kingdom lack cell walls.
Suggest two functions of the eukaryotic cell surface.
Protection & absorption of nutrients. Secretion of signalling molecules. Gas exchange. Cell to cell recognition. Disposal of cellular wastes.
List the proteins which form the cytoskeleton.
Microfilaments (made of actin)
Microtubule (made of tubulin)
Intermediate protofilament.
Describe microfilaments.
The thinnest of the filament types at around 6nm.
Composed of the protein actin.
Organised into a long helical chain.
Where are microfilaments most commonly found?
In the region just below the cell membrane.
Where are microtubules most commonly found?
Radiating from the centrosome.
Where are intermediate filaments most commonly found?
Linking adjacent cells and the extracellular matrix at specific sites.
Describe the structure of Microtubules.
Tubular structures formed from alpha & beta tubulin.
Name the main functions of Microtubules.
1) maintaining cell structure.
2) movement of cell organelles from one part of the cell to another.
3) reorganisation of chromosomes into daughter cells during cell division.
Describe the Microtubule pattern of growth.
They begin to assemble at the centrosome and grow radially outwards. They become stable if they attach to an organelle or capping protein.
What will happen to the shape of a cell if capping proteins become confined to one part of the cell cortex?
Microtubules would only stabilise in that region and the cell would become polarised (take on an asymmetrical shape)
What types of animal cells are inherently asymmetrical in shape?
Neurones and some epithelial cells.
How big are Microtubules?
Much larger than microfilaments. Around 25 nanometers.
What are intermediate filaments?
Filaments in-between the size of microfilaments & Microtubules. They measure around 8-10 nanometers in diameter & are made up,of several different proteins, such as keratin. There purpose is to provide mechanical strength.
What are two of the major activities that take place in the nucleus?
1) DNA replication (the synthesis of new DNA ready for cell division)
2) transcription (production of RNA copies of parts of the DNA sequence)
Where are ribosomes assembled?
In the nucleus.
What are histones?
Proteins which the long double-stranded DNA molecules wind around in order to pack them into tight coils.
Explain the difference between heterochromatin & euchromatin.
Heterochromatin is highly condensed DNA which appears darker and more ‘electron dense’ - it generally contains far fewer genes and is less transcriptionally active.
Euchromatin appears paler & is more transcriptionally active.
What occurs in the nucleolus?
Production of ribosomes
Given the function of nucleolus (or multiple nucleoli) what might it’s size indicate about the activity of the cell?
The presence of a large nucleolus suggests the cell is synthesising a large amount of protein, as the nucleolus is the site of ribosome assembly and ribosomes are required for protein synthesis in the cytosol.
A small nucleolus suggests that a cell is not synthesising much protein.
What is the nuclear lamina?
Intermediate filaments called lamina which form a network of filaments on the inner surface of the nuclear membrane. It is thought to help organise the chromatin.
Describe the nuclear envelope
A double membrane (nuclear envelope) containing nuclear pores about 9nm diameter allowing small water-soluble molecules to diffuse freely.
The nuclear pore complex facilitates the movement of proteins into and out of the nucleus.
