Cell structure & function Flashcards
Cytoskeleton
A complex network of protein filaments found in the cell’s cytoplasm that plays a crucial role in providing structural support, maintaining cell shape, facilitating cellular movement etc.
Properties
Actin filament
also known as Microfilaments
They are long, thin and flexible filaments made of actin proteins. They…
- Consists of two chains of globular actin monomers
- Involved in cell division (actin pinches off the cells from one another)
- Involved in cell movement (interact with motor molecules )
Intermediate filaments
Ropelike assembly of fibrous polypeptides. It consists of 8 tetramers rolled into a ropelike filament bundle .
- Provide structural support to the nuclear envelope.
- Anchor organelles within the cytoplasm.
- Aid in maintaining cell shape.
- Maintain tissue integrity.
Nucleus
Stores DNA and synthesizes mRNA (transcription).
Contains:
* Nucleolus
* Chromatin
* Nuclear lamin proteins
* Nuclear matrix
Nucleolus
A mass of densely stained granules and fibres.
It is the site of ribosomal synthesis and rRNA synthesis
Chromatin
A mixture of DNA and proteins that can form chromosomes
Nuclear envelope
A membrane barrier made up of TWO lipid bilayers that…
- Prevents the free, uncontrolled exhange of molecules between the nucleus and cytoplasm.
- Protects the genetic material.
- Has nuclear pores on its surface for regulated transport of RNA and proteins.
Define
Rough ER
An extensive network of membranous tubules and sacs that…
* Is a continuation of the nuclear envelope.
* Has a large surface area for ribosomes to attach.
* Allows simultaneous production of proteins.
What post-translation modification is undergone in the rough ER
- Glycosylation of polypeptide chain by OLIGOSACCHARYLTRANSFERASE.
- Chaperones begin the folding process.
- Polypeptide chain is transported to the edge of the RER to vesicular transport.
Chaperone protein
A protein that folds polypeptide chains into a smaller volume.
E.g. Calnexin, Calreticulin, BiP
Glycosylation
The covalent attachment of carbohydrates to the backbone of a protein by oligosaccharyltransferase.
- This allows the proper folding of the protein.
- Increases Solubility and stability
What do the ribosomes on the Rough ER membrane do?
- Membrane-bound ribosomes translate mRNA into amino acids.
- Polypetide chain is formed.
Smooth ER
A network of membranous tubules and sacs that…
* Synthesis of lipids (cholesterol and phospholipids)
* Detoxifies the cell (makes harmful substances more water-soluble for easier excretion)
* Stores calcium ions and releases them when required (e.g. muscle contraction,cellular singnalling processes )
* Converts cholesterol into steroid hormones (e.g. cortisol, aldosterone and sex hormones)
* Regulates glycogen metabolism (via enzymes that participate in glycogenolysis and glycogenesis)
Describe the structure & function of the Golgi apparatus
A membrane-bound organelle that consists of a series of cisternae stacked on top of each otherforming different distinct regions cis, medial and trans.
It specialises in modifying, sorting and packaging lipids and proteins into vesicles for transport in the cell or for secretion outside of the cell.
Where does the golgi send proteins?
- Lysosomes
- Cytosol
- Cell membrane
- Secretion (via the cell membrane)
Define
Cytosol
A semi-fluid substance in the cell that helps breakdown waste products
Lysosome
Membrane-bound vesicles produced by the golgi apparatus that contain hydrolytic enzymes for the hydrolysis of mainly proteins.
* Are used in phagocytosis
* Are used in apoptosis
What is a perixosome and its function
A membrane-bound organelle that is responsible for the breakdown of lipids and fatty acids.
It also protects the cell from reactive oxygen species
Contains oxidative enzymes
Define
Mitochondria
An organelle with two lipid bilayers that is responsible for cellular respiration via glycolysis etc.
They are self-replicating due to them having their own DNA.
TRUE OR FALSE
Energy to make ATP comes from glycolysis
FALSE
The energy comes from protons moving down their electrochemical gradient into the mitochondrial matrix from the intermembrane space.
Function
Intermediate filaments
They create cell cohesion and provide a stable structure.
Funcion
Microfilament
- Cell motility
- Exocytosis
- Endocytosis
- Secretion
TRUE OR FALSE
A centriole is made up of 3 centrosomes
FALSE
A centrosome is a membrane-bound organelle that consists of two centrioles
Define
Centrosome
A membrane-bound organelle made up of two centrioles.
It is involved in cell motility and regulating cell division via mitotic spindle assembly.
Eukaryotic Ribosome
- 80S
- Made up of rRNA and protein
- Comprised of two subunits (60S and 40S)
In the small subunit the mRNA binds and is decoded whereas in the large subunit, amino acids are joined up forming a polypeptide.
Describe the cisternal maturation model and how it benefits the golgi
The cisternal maturation model consists of the cis ,medial and trans compartments. As the proteins progress through these networks they undergo post-translation modification.
* The cis region faces the ER and is where proteins and lipids gain entry to the golgi.
* The trans region is where the vesicle packaging occurs and secretion occurs.
This structural organization allows for efficient compartmentalization and sequencial processing .
What are cisternae
Flattened membrane-bound sacs found in the ER and Golgi apparatus
How is the destination of a protein/lipid determined by the golgi
Golgi bodies contain resident-proteins that can recognise specific signals ‘tagged’ on the protein/lipids by the ER. These signals dictate where they will be transported to by the golgi.
Nuclear matrix
A protein scaffold in the nucleus that…
* Provides structural support for the nucleus.
* Aids in the spatial organization of genes.
* Facilitates the movement of genetic material during DNA replication and transcription.
Nuclear lamina
Intermediate filaments lined on the inner surface of the nuclear envelope that…
* Provide mechanical support by maintaining the shape of the nucleus.
* Help with chromatin organization.
* Help with gene regulation.
Microtubule
Small, hollow cylinders of 13 rows of tubulin dimers. Consist of alpha and beta tubulin. Due to this combination of blocks it results in polarity. They…
* Assemble/disassemble quickly through the addition/removal of tubulin dimers
* Ergo MT can grow or shrink rapidly.
* They act as ‘tracks’ for motor molecules
* All are anchored to the centrosome (with their negative ends tethered).
* Cilia and flagella are made up of MT
Cell membrane
A crucial barrier that separates the external and the internal environment. It has…
* lipid bilayer that consists of hydrophobic tails and hydrophilic heads. The sandwiched hydrophobic tails prevent the free movement of water molecules across the membrane.
* Integral proteins
* Peripheral proteins
* Carbohydrates bind to either lipids (glycolipids) or proteins (glycoproteins)
Integral proteins
Proteins that span the entire lipid bilayer. These often are transmembrane proteins (channels/pumps)
Peripheral proteins
Proteins that are are attached to either the outer or inner surface of the cell membrane. The often bind to the hydrophilic regions of integral proteins.
They are held in place by the cytoskeleton (if they are on the cytosolic side) or by extracellular matrix (if they are outside the cell)
Glycoproteins | Glycolipids
These act as ‘tags’ for cell-cell recognition. Their diversity and location determine them as specific markers for different cell types.
What substances require transport proteins to pass the cell membrane and why?
Charged polar molecules and ions tend to have low permeability and therefore require transport proteins.
* Ions
Na+, K+, Cl-, Mg2+, Ca2+
* Amino acids
* ATP
* DNA & RNA
* Glucose
Tonicity
The ability of a solution to alter the water concetration in a cell.
Isotonic
A system in which there is an equal concentration of solutes outside the cell as there is inside the cell
Hypotonic solution
Solute concentration is lower outside the cell.
Water diffuses into the cell causing it to swell and possibly rupture.
Hypertonic solution
Solute concetration is higher outside the cell.
This means that water will diffuse out of the cell causing it to ‘shrink’
Exocytosis
The fusing of a vesicle with the cell membrane allowing the release of the macromolecules outside the cell.
Types of endocytosis
- Phagocytosis
- Pinocytosis
- Receptor-mediated endocytosis
Endocytosis
A process in which macromolecules fuse into small sinks in the membrane which are eventually pinched into vesicles inside the cell.
[Movement into the cell]
Pinocytosis
A type of endocytosis in which the cell engulfs extracellular fluid and solutes into the cell.
During this process, the cell membrane invaginates the material by forming small vesicles called pinosomes.
Phagocytosis
Phagocytosis is a type of endocytosis in which the cell engulfs larger particles, such as bacteria, cell debris, or other solid substances, by forming large vesicles called phagosomes.
