Lecture Nine - Organelles in eukaryotes Flashcards
Define prokaryotic and eukaryotic cells.
Eukaryotic - An organism consisting of a cell or cells in which the genetic material is DNA in the form of linear chromosomes contained within a membrane bound nucleus. Eukaryotes include all living organisms other than the eubacteria and archaea.
Prokaryotic - A single-celled organism which has neither a distinct nucleus with a membrane nor other specialised organelles, including the bacteria and cyanobacteria. Has circular chromosomes located in nucleoid regions of the cell.
What is the endomembrane system?
A system of internal, membrane bound compartments within the cell that can form physical links to exchange components. Includes: Nuclear envelope (nucleus). Endoplasmic reticulum. Golgi body. Lysosomes and vacuoles.
What is the nucleus?
Contains the DNA, organised so that genes are held in specific positions.
Nucleolus produces ribosomal RNA and assembles ribosomes.
Enclosed by the nuclear envelope.
Inner membrane supported by the nuclear lamina.
outer membrane supported by the cytoskeleton.
Nuclear pore complexes in the envelope regulate entry and exit.
Nuclear envelope is continuous with the ER.
What are ribosomes?
Follow the path of information: DNA –> mRNA –> Protein.
Large subunit and small subunit.
Consist of ribosomal RNA and proteins.
Carry out protein synthesis (translation).
free in the cytoplasm or bound to the membrane of the ER.
What is the endomembrane system?
In the endomembrane system: Nuclear envelope. Endoplasmic reticulus. Golgi body. Lysosomes. Vesicles and vacuoles. Plasma membrane.
Not in the endomembrane system:
Mitochondria.
Chloroplasts.
Peroxisomes.
What is the endoplasmic reticulum?
A biosynthetic factory for lipids, glycoproteins etc.
Smooth ER: Metabolises CHO's. Makes lipids, phospholipids and steroid hormones. Detoxification of drugs/poisons. Stores calcium.
Rough ER:
Bound ribosomes.
Proteins are passed into the lumen (membranes surround an inner cavity called the lumen, basically a compartment for storage of substances that must be kept separate from the cytoplasm).
CHO’s can be added - glycoprotein.
Makes phospholipids and proteins - assembles membranes.
What is the golgi body?
Sorts, packages and sends proteins.
Vesicles fuse at the cis-golgi to form new cisternae (long vesicle).
Cisternae ‘mature.’
Vesicles bod off the trans golgi.
Vesicles have proteins which target them to particular organelles.
What are lysosomes?
Vesicles full of hydrolytic (digestive) enzymes.
A highly acidic environment.
Phagocytosis - food form outside the cell is phagocytosed.
Macrophages are white blood cells that engulf bacteria.
Autophagy - Breaking down damaged organelles for recycling.
What are vacuoles?
Vacuoles in single celled animals are usually contractile water expulsion vacuoles.
Can be found in most plant cells and give young tissue physical support.
Plant cell vacuoles also store ions, toxic waste product and defence chemicals (when something eats the plant, the vacuole is split and poisons the thing eating it).
What are peroxisomes?
Not part of the endomembrane system.
Peroxisomes - oxidative organelles that transfer hydrogen form various compounds to oxygen, forming hydrogen peroxide. E.g. detoxification of alcohols by the liver.
Glyoxysomes - Specialised peroxisomes in plant tissue.
Break down fat reserves in seeds to produce sugars for the growing seedling.
What is the endosymbiont theory?
Chloroplasts and mitochondria derive from ancestral prokaryotes that became symbionts.
An ancestral eukaryote engulfed an oxygen using (but non photosynthetic) prokaryote and a photosynthetic prokaryote.
What is the mitochondria?
Have an enclosing outer membrane.
Internal highly folded membrane - the cristae, enclosing the matrix.
Found in almost all eukaryotic cells.
Responsible for the synthesis of ATP from stored components.
What are chloroplasts?
Have two enclosing outer membranes.
Internal elaborately folded specialised membrane system - the thylakoid membranes.
Found in many plant cells exposed to the light.
Responsible for conversion of light energy into chemical energy - ATP and other energy currency.
What is the cytoskeleton?
Assists with movement in cells, movement of vesicles/organelles, and overall cell structure and shape.
Explain the organisation of microtubules.
Constructed from dimers of alpha tubulin and beta tubulin.
Very dynamic assembly/disassembly.
One end can be grown/shrunk much faster than the other.
Are usually ‘organised’ by an organising centre.
E.g. A centrosome during cell division in animals.
