15-09-21 - Cells and Organelles 2 Flashcards
1
Q
How do vesicles/organelles move away and towards the Golgi?
What determines what direction they will move in?
What else can this method be used for?
A
- Vesicle cargo sits on top of motor proteins and use microtubules as a track to move towards or away from the Golgi.
- Microtubules have polarity, meaning they have a positive and negative end
- The vesicle will move in a certain direction, based on the charge of the motor (positive or negative) in relation to the polarity of the microtubule.
- Typically, the negative end of a microtubule is embedded in the mass of protein called the centrosome in the middle of the cell (next to Golgi) and positive end towards the plasma membrane.
- Other organelles may also be moved using microtubule tracks.
- This is how the cell becomes organised.
- This would mean a negative end motor drives vesicles from the Golgi to the plasma membrane and a positive end motor would drive vesicles from the plasma membrane to the Golgi.
2
Q
Where are microtubules found?
What is the structure made from?
Where is it found?
A
- Microtubule tracks usually originate from the centrosome (the centre for organising microtubules)
- The centrosome is a mass of protein in the middle of the cell next to the Golgi.
- The centrosomes contain 2 centrioles
- Centrioles are an array of 9 microtubule triplets.
3
Q
Give a brief explanation of uptake and degradation.
How is uptake done?
What organelles is cargo delivered to?
A
- Uptake is done by endocytosis.
- The membrane/ cargo is brought into the cell and delivered to endosomes, then passed to lysosomes for degradation.
- Some membrane is recycled back to the cell surface to be used again.
4
Q
What is autophagy?
How does the process occur?
What triggers it?
A
- Autophagy is a type of degradation in which parts of the cell are walled off and digested in the lysosomes.
- The cell invaginates (makes a membrane around) parts of the cell (organelles and cytosol)
- This closes in a membrane which is delivered to the lysosomes for degradation.
- Autophagy can occur with the appropriate signals, such as starvation.
5
Q
What are the 3 methods of endocytosis
Are they specific or non-specific?
What molecules are they used for?
A
- Phagocytosis (cell eating) – For larger particles like yeast and bacteria
- Pinocytosis (cargo uptake – non-specific) – for smaller molecules
- Receptor mediated endocytosis (selective uptake of cargo – highly efficient) – cargo binds to receptors collected in the coated pits of membranes.
- These receptors with cargo then invaginates into and pinches off the cell membrane into the cell.
6
Q
What are lysosomes?
How are they specialized?
What is their purpose?
A
- Lysosomes are specialised membrane-bound organelles in the cell
- They are specialised as they have a low pH of 5 and they contain hydrolytic enzymes.
- Lysosomes act as recycling containers.
- The hydrolytic enzymes chop up cargo delivered for degradation into smaller components.
- The smaller components are then transported into the cytosol to be used by the cell.
7
Q
What do endosomes act like during uptake and degradation?
Why are the endosomes so essential during uptake and degradation?
A
- The endosome acts as the Golgi would during this process.
- The endosomes are important as during endocytosis, cargo as well as membrane components used for uptake are taken into the cell.
- We don’t want to degrade membrane components used for uptake, we want to recycle them, this is what the endosome system is responsible for.
- Without the endosomes, there would only be uptake and degradation, which would lead to the degradation of the cell in a couple of hours.
8
Q
Where are proteins for the upgrade and degradation systems formed?
How are they distinguished?
A
- Membranes of RER, Golgi, secretory vesicles, plasma membrane, lysosomes and endosomes are all made on RER.
- These proteins are diverted by special sequences (sorted away from secretory pathway) in the Golgi.
9
Q
What is another method of degradation?
How does it differ from degradation in lysosomes?
What is responsible for it?
Give a brief explanation of the process
A
- Degradation can happen in the cytosol without membranes (lysosomes)
- This is known as protein degradation and is done by the protein complex proteasome
- Junk protein is tagged with ubiquitin
- The protein is then recognized by proteasome, fed into proteasome and chopped into component fragments.
10
Q
Why is protein turnover essential in cells?
What can happen if the processes become deficient?
A
- Protein turnover is essential for cells to function efficiently.
- If some of these processes become deficient, this can lead to neurodegenerative diseases such as Alzheimer’s or Parkinson’s.
11
Q
What is compartmentalization?
Why is it useful for eukaryotic cells?
Give an example
A
- Compartmentalisation is the formation of internal membrane compartments with a range of specialised functions.
- This allows for specialised reactions (that can be potentially harmful) to be separated from the rest of the cell, concentrated and optimized.
- An example of this are the lysosomes.
- They have a pH of 5 and hydrolytic enzymes, which could harm the rest of the cell.
- Compartmentalization ensures they are kept separate.
12
Q
What is a consequence of membrane compartments?
What do vesicles do?
What does this maintain?
A
- Vesicle transport is a consequence of membrane compartments
- Vesicles transport membrane and cargo between compartments
- This selective transport maintains composition of membrane compartments
13
Q
Describe what aids vesicle formation
Describe the process of vesicle transport between compartments/to extracellular environment
A
- Vesicle budding is aided by molecular scaffold supports, which are important for bending and maintaining curvature (vesicle coats - ex clathrin)
- Vesicle coat assembles to form vesicle and pull-out cargo from organelles
- This is done by the vesicle coat binding receptors, which bridge through the membrane to bind the cargo.
- The vesicle then pitches off from the organelle via endocytosis.
- Once the cargo crosses from the organelle into the cytosol, the cargo is in the exoplasmic compartment (the outside equivalent of the cell)
- The vesicle can now fuse with an organelle or the plasma membrane.
14
Q
How did mitochondria become a part of cells?
What advantages did it bring?
What followed?
A
- About 2 billion years ago, a large non-nucleated cell (archaea) engulfs a bacterium.
- The bacterium provided energy (ATP) + multiplied to provide energy for growth (bigger cells become possible)
- During further evolution, cell membrane invaginates to form internal membranes – Segregation of protein synthesis on ER and ER coats nucleoid to form nuclear envelope.
15
Q
What are 4 features of mitochondria?
How do they reproduce?
Where are all mitochondria inherited from?
A
- Produce most of ATP supply
- Enabled cells to grow bigger
- Present in all eukaryotic cells
- Two membranes – inner membrane folded into interior
- Contain their own DNA – reproduce by dividing in two
- All mitochondria come from mothers’ egg
17
Q
What 3 things does the Cytoskeleton consist of?
A
- Microtubules
- Microfilaments
- Intermediate Filaments
18
Q
Microtubules – size, functions, subunits, features
A
- Size – 25nm (thickness of ribosomes)
- Functions – Vesicle tracks, positioning and movement of organelles during cell division
- Subunits – tubulins
- Features – dynamic, has positive and negative end (polarity)
19
Q
Microfilaments – size, functions, subunits, features
A
- Size – 7nm
- Functions – generate contractile forces, enabling cells to move, parts of cells to move, and cells to contract
- Subunits – actin and myosin (allows for motility)
- Features –
20
Q
Intermediate filaments – size, functions, subunits, features
A
- Size – 10nm
- Functions – strength, support.
- Subunits – keratins (in cytoplasm), lamins (supports nuclear envelope)
- Features – stable, not dynamic
21
Q
Two organelles prominent in a few specialised cell types and their functions
A
- Smooth ER
- Connected domain of RER membrane with no ribosomes
- Involved in lipid and steroid production and detoxification.
- Peroxisomes
- Break down some fatty acids.
- Synthesise some specialised lipids (e.g nervous system)
- Perform oxidative reactions using molecular oxygen – these generate hydrogen peroxide, with excess broken down with catalase
22
Q
Label this cell diagram and describe what each organelle does.
- Nucleus
- Nucleolus
- Mitochondria
- Ribosomes
- Golgi apparatus
- RER
- Smooth ER
- Endosomes
- Lysosomes
- Plasma membrane
- Secretory vesicles
- Peroxisomes
A
- Nucleus – Directs cell activities and contains genetic material in the form of chromosomes
- Nucleolus – site of ribosome production at amplified ribosome genes
- Mitochondria – Responsible for most of ATP made in cell.
- Ribosomes – site of translation and formation of proteins
- Golgi apparatus – Receives output from RER, Modifies lipids/proteins, sorts and packages cargo into distinct vesicles for export to other organelles.
- RER – production, folding, quality control and dispatch of some proteins. Synthesizes proteins for plasma membrane. Can trigger stress signals.
- Smooth ER – involved in lipid and steroid production and detoxification
- Endosomes – sorts cargo for lysosomes and recycles membrane components for endocytosis.
- Lysosomes – Acts as recycling container. Chops up delivered cargo using hydrolytic enzyme and delivers it to the cytosol to be used by the cell.
- Plasma membrane – gives cell protection, allows cell to act as individual unit by acting like a reaction contained. Controls movement of molecules in and out of cell.
- Secretory vesicles – Play important role in moving molecules outside of the cell via exocytosis.
- Peroxisomes – Break down some fatty acids, synthesises specialised lipids, performs oxidative reactions using molecular oxygen
