B2.2 Flashcards
What are examples of organelles?
RER
SER
ribosomes
Etc
What classifies you as an organelle?
Must have a specific function and must also be discrete
Differences in membranes and examples
No membrane - not enclosed by a phospholipid bilayer and an example is ribosomes
Single membrane bound - sacs enclosed by a single phospholipid bilayer and an example is RER and SER
Double membrane bound - structure enclosed by two phospholipid bilayers and an example is the nucleus
What is differential centrifugation?
Involves disrupting cells in a homogeniser (blender) and centrifuging the resulting mixture and separating the supernatant (remaining liquid) into components, through repeated centrifugation.
Advantages of the separation of the nucleus and cytoplasm into separate compartments
Allows cytoplasm to send signals to the nucleus and the cytoplasm receives an extracellular signal such as a hormone or growth factor
Nucleus contains the cells DNA and it regulates genes through the transcription of DNA into mRNA
Cytoplasm responsible for metabolic processes involving translocation or mRNA into proteins on the ribosomes
Advantages of compartmentalisation in the cytoplasm of cells
Small volumes allows enzymes and their substrates to be concentrated, speeding up enzyme activity
pH can be kept at the ideal level for the organelles function
Substances that can damage cells can be isolated within a membrane, protecting remaining structures from degradation
Example: lysosomes
Contain many hydrolytic enzymes that digest proteins and other macromolecules
PH kept at 5 for acid hydrolyses which actively concentrate H+ ions. They also provide double protection against uncontrolled digestion of the contents of the cytoplasm
Adaptations of the mitrochondrian for production of ATP by aerobic respiration
Outer membrane - contains transport proteins that enable the shuttling of key materials from the cytosol.
Inner membrane - contains the electron transport and ATP synthase (used for phosphorylation)
Cristae - the inner membrane is arranged into folds that increase the SA:VOL ratio.
Intermembrane space - small space between membranes maximises hydrogen gradient upon proton accumulation
Matrix - central cavity that contains appropriate enzymes and a suitable pH for the krebs cycle to occur
Adaptations of the chloroplast for photosynthesis
Stroma - central cavity that contains appropriate enzymes and a suitable pH for the Calvin cycle to occur
Thylakoids - are arranged into stacks to increase SA:VOL ratio of the thylakoid membrane
Photosystems - pigments organised in thylakoid to maximise light absorption
Lamelle - connects and separates grana, maximising photosynthetic efficiency
Functional benefits of the double membrane of the nucleus
Didn’t really know how to write this one so look in book but here is a quick answer
The nuclear membrane serves to separate the chromosomes from the cell’s cytoplasm and other contents. An array of small holes or pores in the nuclear membrane permits the selective passage of certain materials, such as nucleic acids and proteins, between the nucleus and cytoplasm.
Nucleus during cell division
Nucleus can disassemble and re-form each time most cells divide
Prophase - nuclear membrane and endoplasmic reticulum are fragmented into vesicles. Move to edge of cell
Telophase - vesicles are moved around the new sets of daughter chromosomes and ER and nuclear membrane reform
Structure and function of free ribosomes and of the RER
Ribosome
Site of polypeptide synthesis within the cell. Composed of protein providing stability and ribosomal RNA
Comprised of two distinct subunits:
Small subunit responsible for binding to mRNA, while the large subunit binds to tRNA and when the two subunits form a complex, translation of an mRNA sequence can occur
Free ribosomes synthesise proteins for use within the cytosol and ribosomes embedded within the RER synthesise proteins that will be packaged up into vesicles and transported to other organelles
Structure and function of the Golgi body
Function: responsible for sorting, storing, modifying and exporting cellular material
Structure:
Composed of flattened sacs (cisternae) that are located between the ER and the plasma membrane
Proteins from RER and lipids from SER arrive in vesicles and are modified into functional molecules
Different sacs responsible for specific chemical modifications based on enzymes involved such as phosphorylation
Things that pass through the Golgi body include the secretory proteins and glycoproteins
Constitutive secretion
Immediate release triggered by a ligand (external chemical signal) binding to a specific receptor.
Regulatory secretion
Sustained release triggered by a ligand (external chemical signal) binding to a specific receptor
Clathrin
Coat protein that helps vesicles form
Triskelion-shaped molecule that is recruited to a membrane by adaptor proteins (adaptin)
Link together to form a rounded lattice that pulls the membrane into a bud which is then cleaved (chopped) by another protein (dynamin) to form a vesicle at which point the Clathrin architecture disassociates
Receptor-mediated endocytosis
Clathrin required which is recruited by ligand which binds to a receptor
Advantage: only specific ligand will be internalised, allowing greater regulatory control over what materials enter a cell
