Eukaryotic Cells Flashcards
What are Eukaryotic cells?
Bigger and more complex than prokaryotes. Very diverse
What are the relative sizes of Eukaryotic and Prokaryotic cells?
E = 10 -100 micrometres P= 1 - 5 micorometres
What are some features of eukaryotes?
- Intracellular compartmentalization (organelles)
- Nucleus
What makes Red Blood Cells different from other eukaryotes?
- No nucleus
- Must have had one to begin with in order to differentiate and replicate
- Lost in when they became specialised
Describe the structure of the nucleus.
- Largest organelle
- Contains most of the genetic material
- Nucleolus
- Nuclear Envelope
Describe the function of the nucleus.
- Store genetic material
- DNA strands packaged with histones - condensed
- Transcription
How does dividing trnascription and translation allow for regulation?
Transcription - nucleus. Translation - cytoplasm. mRNA needs to be moved. Process regulated.
Describe the nuclear envelope
- Selective openings to allow mRNA out
- Some proteins may need to be moved back into the nucleus
Describe the structure of ribosomes
- Ribonucleoprotein complexes
- Large and small subunits
Describe ribosome assembly
- Transcription → nucleus
- Translation → cytoplasm
- Polypeptide assembled onto nascent rRNA → nucleolus
- Subunits transported to cytoplasm for function
Describe the function of the ribosome
- Translate mRNA into proteins
What happens in if the protein is destined to remain in the cytosol?
Translated by ribosomes free in the cytosol
What happens if the protein is destined to be secreted?
- Translated by proteins on the RER
- Enter the secretory pathway
Describe the process of translation for proteins destined to remain in the cytosol
- Polypeptide emerges
- Folds as its emerging from the ribosomal tunnel
- Chain grows more ribosomes attach to create a polysome
- Once a stop codon is reach the polypeptide is released
Describe the process of translation for proteins destined to be secreted.
- Short hydrophpbic section emerges first
- Known as a signal peptide
- Recognised by the signal recognition peptide
- Halts translation
- Carries the ribosome to the RER
- Ribosome attaches to the RER
- Polypeptide grows again
Outline the secretory pathway
Recognition of signal pathway - Golgi - Secretory Vesicles - Fused with the membrane - Released
What is glycosylation?
Form of post translational modification. Addition of carbohydrates. Diverse
Describe how post translational modification works
- Different enzymes are housed in different membrane bound compartments (cisternae)
- Proteins travel through in a different and specialised order
- Golgi is like an assembly line
- Cell ensures they move through in a defined order
- Receiving sequential modifications
What is the trans golgi network?
- Sorting station
- Part of the endocytic pathway
- Interconnected tubules and vesicles
- Proteins trafficked through the ER are packaged into secretory vesicles that fuse with the plasma membrane to leave the cell
What is endocytosis?
Taking in
Describe endocytosis
Portion of plasma membranes invaginates and pinches off to form a vesicle called an endosome
What does the lysosome do?
Degradative enzyme. Proteases and lipases
What does compartmentalisation allow for?
- Coordination/regulation of complex of biochemical reactions
- Sequestrations of components
- Energy generation
How do you move molecules between organelles?
- Vesicular transport
- Need a high level of communication
What is autoradiography?
- Bio-analytical technique - helps visualise the distribution of molecules labelled with radioisotope
- Can localise molecules within tissues etc
- Sensitive and quantitative
- Works by incorporating radioisotopes into molecuels, energy emitted can be deteced
What is Pulse chase labelling?
- Incorporate radioactive isotopes into molecules synthesized during a defined time period
- Radio-labelled compound added to system of choice for a brief period of time (the ‘pulse’)
- (the ‘chase’) is initiated by either washing the sample to remove the isotope and/or adding excess non-labelled compound
- Used to follow the dynamic of cellular processes and pathways
Describe an a specific pulse chase labeling experiment
- Slices of pancreas in culture synthesisze and secrete enzyme
- Add 3Hleucine become incorporated into newly synthesized proteins
- After 10’ wash the slices and initate ‘chase’
- Perform audioradiography after 0, 10 and 60 minutes
Where do proteins enter the secretory pathway?
RER
What was the SNARE hypothesis proposed to explain?
Specificity of vesicular transport
What do free cell assays allow scientists to do?
Identify new physiological processes
what are the 2 types of SNARe PROTEINS?
- v-Snare on vesicles
1. t-SNARE on target membranes
describe the process of SNARE proteins.
- on trnasport vesicles
- v SNARE recognises its partner t SNARE on appropriate target membrane
- binding docks the vesicle onto target membrane and recruit machinery that meidates mebrane fusion
what does SNARE stand for>
Soluble NSF attachment receptors
outline the SNARE hypothesis
- a family of proteins that localize to different intracellular
organelles - Transport vesicles carry specific v-SNAREs (1 mark)
that recognize and bind to t-SNAREs - Membrane fusion can only proceed following formation of a functional
SNARE complex
how is molecular machinery required for membrane traffic evolutionary conserved?
- Sequence analysis of mammalian NSF and yeast Sec18 revealed homology
- cDNA encoding NSF
- complements the growth phenotype
of sec18 mutant yeast
evidence that indicates cell to cell signalling
single celled eukaryotes like yeast use secreted cell signals to signal
mating-type during sexual reproduction
