Basic Cell Structure Flashcards
What are the main differences between prokaryotes and eukaryotes?
Prokaryotes
- No nucleus; plasmids + free DNA
- No membrane-bound organelles
- Peptidoglycan cell wall
- 1-10 um
Eukaryotes
- Nucleus; several chromosomes
- Membrane-bound organelles
- No cell wall
- 10-100 um
Why are chemical reactions more efficient in eukaryotic cells than prokaryotic cells?
- Eukaryotic cells are compartmentalised by internal membranes (membrane-bound organelles) - more efficient reactions.
- In prokaryotes, all biochemical processes occur in the same compartment.
What is the largest organelle and describe its structure.
- Nucleus
- Surrounded by nuclear envelope containing nuclear pores.
- Contains nucleolus (forms ribosomes).
How is DNA packaged inside the nucleus?
- Folded into nucleosomes using histones - chromatin.
- Heterochromatin (10%): remains packed after mitosis (solenoid), transcriptionally inactive.
- Euchromatin: beads-on-a-string, transcriptionally active.
Which structures envelope the cell?
- Plasma membrane (plasmalemma)
- Glycocalyx
What is the PM made up of?
- Specific proteins, lipids and carbs.
- Amphipatic phospholipids (hydrophilic heads and hydrophobic tails) assemble into a lipid bilayer - forms a relatively impermeable barrier to most water-soluble molecules.
What is the fluid mosaic model?
- Proteins ‘swim’ in the fluid lipid layer and mediate most membrane functions.
- Lipid rafts = membrane regions that assemble specialised proteins and lipids to perform a certain task.
What is the glycocalyx?
- Cell coat made up of oligosaccharide and polysaccharide side chains of glycoproteins on the outside of the plasmalemma.
- This glycosylation often changes the function of the associated protein.
Give examples of how membrane proteins can be associated with the lipid bilayer in different ways.
- Integral membrane proteins: contain hydrophobic membrane-spanning domains (e.g. Alpha-helix) that interact with the phospholipid fatty acyl groups.
- Peripheral membrane proteins: bound indirectly to membrane via interactions with integral membrane proteins or with lipid polar head groups.
Name the functions of the PM.
- Selective permeability
- Transport of materials along cell surface
- Endo- and exo-cytosol
- Intercellular recognition and adhesion
- Signal transduction
Which organelles are involved in protein synthesis? What is the structure of these?
- Ribosomes
- 2 large subunits made up of ribosomal RNA and proteins
- Located free in cytoplasm or associated with rER
What is the ER?
- Membranous extension of nuclear envelope.
- Involved in: synthesis and transport.
- 2 types that are continuous.
What are the different functions of the 2 types of ER?
- Smooth ER (no ribosomes).
- Involved in:
A) lipid synthesis
B) metabolism of carbohydrates
C) detoxification of drugs/poisons
D) calcium storage (for cell signalling)
- Less common type - Rough ER (ribosomes)
- Involved in: secretory enzyme processing
In which cell types is sER more commonly found in?
- Liver cells and mammary glands (lipid biosynthesis)
- Ovary, testis and adrenal gland (steroidogenesis)
What is the function of the Golgi apparatus?
Modifies (e.g. O-glycosylation), sorts, concentrates and packages proteins synthesised on the rER.
What are the 2 faces of the Golgi called and where does vesicle budding take place?
- Cis
- Trans (vesicle budding)
Name the components of the Golgi.
- Cis Golgi network
- Golgi stack: cis cisterna, medial cisterna and trans cisterna
- Trans Golgi network
What are the 3 fates of proteins exiting the Golgi?
- Constitutive secretion - targeted to PM
- Regulated secretion - signal-mediated diversion to secretory vesicles
- Signal-mediated diversion to lysosomes
What are lysosomes?
- Single-membrane organelles generated by the Golgi
- Degrade unwanted material, inc. pathogens
How do lysosomes degrade material?
- Contain many hydrolytic enzymes
E.g. Nucleases, proteases, glycosidases, phosphatases and phospholipases. - Very acidic environment maintained by vacuolar H+ ATPase (proton pump)
How is the membrane of lysosomes protected from enzyme damage?
Coated by a specialised glycocalyx.
What are peroxisomes and what is their function?
- Multi-purpose single membrane-bound organelles that contain many enzymes (crystalline core).
- Functions include:
- hydrogen peroxide (H2O2)/ROS metabolism
- lipid metabolism (e.g. Fatty acid beta-oxidation, phytanic acid alpha-oxidation)
- detoxification (oxidise) of a number of molecules inc. alcohol, phenols, formic acid and formaldehyde (in liver and kidney cells)
What is the function of mitochondria?
Energy production: use sugars, fats and oxygen to produce ATP via oxidative phosphorylation using ATP synthase.
Describe the structure of mitochondria.
- Double membrane (separated by intermembrane space):
- inner membrane folds to form cristae. Contains enzymes for oxidation reactions of respiratory chain.
- outer membrane
- Matrix: contains 100s of enzymes, ribosomes and mitochondrial DNA genome
