B2.2 Organelles and compartmentalization Flashcards by Ebba Löfgren

B2.2.1 What are organelles and why are they useful?

Discrete structures in cells adapted to perform one or more vital functions.
Efficient because they are specialized.

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B2.2.1 Cell components that aren’t organelles

Cell walls = extracellular structures (outside PM)
Cytoskeletons = narrow protein filaments spread throughout cell, not discrete enough.
Cytoplasm = not a discrete structure, many different structures and performs many functions.

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B2.2.1 Organelles membranes (no, single, double)

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B2.2.2 Advantage of the separation of the nucleus and cytoplasm - DNA + RNA

Chromosomes in nucleus = safeguards DNA
Transcription and RNA processing is in the nucleus, transport cytoplasm for translation: better quality control + gene regulation.

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B2.2.3 Advantages of Compartmentalisation - enzymes

Enzymes and substrates for a particular process can be much more concentrated than if they were spread throughout the cytoplasm.

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B2.2.2 Advantage of the separation of the nucleus and cytoplasm - signalling

Cytoplasm receives signals, e.g. hormones, relays to nucleus. This regulates transcription, altering gene expression.

Allows the cell to adjusts protein production to adapt to different conditions.

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B2.2.3 Advantages of Compartmentalisation - organelles (conditions, substances, contents)

Substances that could damage the cell can be kept inside the organelle membrane. E.g. digestive enzymes of a lysosome could digest a cell.

Conditions e.g. pH can be maintained at optimal levels for specific process, different from other cell parts.

Organelles with their contents can be moved around within the cell.

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B2.2.3 Advantages of Compartmentalisation - membrane potential

There is a larger area of membrane available for processes that happen within or across membranes.

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B2.2.4 (HL) Adaptations of the mitochondrion - outer membrane

Contains transport proteins that enable the shuttling of key materials from the cytosol.

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B2.2.4 (HL) Adaptations of the mitochondrion - inner membrane

Contains the electron transport chain and ATP synthase (used for oxidative phosphorylation).

Arranged into cristae that increase the SA:Vol ratio.

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B2.2.4 (HL) Adaptations of the mitochondrion - intermembrane space

Small space between membranes maximises hydrogen gradient upon proton accumulation.

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B2.2.4 (HL) Adaptations of the mitochondrion - matrix

Central cavity that contains appropriate enzymes and a suitable pH for the Krebs cycle to occur.

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B2.2.5 (HL) Adaptations of the chloroplast for photosynthesis - thylakoids

Flattened discs = small internal volume to maximise hydrogen gradient upon proton accumulation.

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B2.2.5 (HL) Adaptations of the chloroplast for photosynthesis - grana

Thylakoids are arranged into stacks to increase SA:Vol ratio of the thylakoid membrane.

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B2.2.5 (HL) Adaptations of the chloroplast for photosynthesis - photosystems

Pigments are organised into photosystems in thylakoid membrane to maximise light absorption.

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B2.2.5 (HL) Adaptations of the chloroplast for photosynthesis - stroma

Central cavity that contains appropriate enzymes and a suitable pH for the Calvin cycle to occur.

B2.2.5 (HL) Adaptations of the chloroplast for photosynthesis - lamellae

Connects and separates grana, maximising photosynthetic efficiency.

B2.2.6 (HL) Nucleus structure

The semifluid matrix found inside = nucleoplasm.

DNA within the nucleus is found as chromatin, less condensed form that organizes to form chromosomes during prophase of mitosis/meiosis.

A nucleolus/nucleoli, organelle synthesizes ribosomes.

B2.2.6 (HL) Functional benefits of the double membrane of the nucleus - nuclear envelope

A system of two concentric membranes, inner and outer nuclear membrane.

Outer = continuous with endoplasmic reticulum.

Are phospholipid bilayers, which are permeable only to small nonpolar molecules.

B2.2.6 (HL) Functional benefits of the double membrane of the nucleus - nuclear pores

Create a selective passageway through which molecules are able to travel between the nucleus and the cytoplasm.

B2.2.6 (HL) Functional benefits of the double membrane of the nucleus - nuclear pores transport

Proteins for genome structure and function, e.g. histones, made in cytoplasm + imported into nucleus.

mRNA and tRNA transcribe in the nucleus, exported for translation. Ribosomes synthesized in nucleolus exported to the ER or cytoplasm to aid translation.

B2.2.6 (HL) Nucleus During Cell Division

Disassembles and re-forms when most cells divide.

Prophase: nuclear membrane and ER are fragmented into vesicles which are moves to the edge of the cell.

Telophase: vesicles moved around the daughter chromosomes, nuclear membrane and ER reformed.

B2.2.7 (HL) Structure of free ribosomes and of the rER

Site of polypeptide synthesis. Protein (stability) and rRNA.

Small subunit: binds to mRNA
Large subunit: binds to tRNA

Two subunits form a complex = translation of an mRNA sequence occurs.

B2.2.7 (HL) Function of free ribosomes and of the rER

Free ribosomes synthesise proteins for use within the cytosol (i.e. intracellular proteins).
rER Ribosomes: synthesise proteins to be packaged into vesicles + sent to organelles.

Vesicles transported to Golgi a. = proteins secreted for extracellular use.

B2.2.8 (HL) Function of the Golgi apparatus

Sorts, stores, modifies and exports cellular material. Proteins (from rough ER) and lipids (from smooth ER) arrive in vesicles at the Golgi body and are modified into functional molecules.

B2.2.8 (HL) Structure of the Golgi apparatus

Composed of flattened sacs (cisternae) located between the ER (cis facing) and PM (trans facing) Different sacs = responsible for specific chemical modifications based on the enzymes involved.

B2.2.8 (HL) Secretion from the Golgi apparatus

Materials for secretion are packaged into vesicles at the Golgi body for extracellular release (exocytosis). * Constitutive secretion: immediate release. * Regulatory secretion: stored in secretory vesicles for a sustained release. Triggered by a ligand binding to a specific receptor.

B2.2.9 (HL) Structure and function of vesicles in cells

Membrane-wrapped containers involved in shuttling materials between cellular compartments. Large molecules are packaged into vesicles that fuse with membranes to deliver extracellular material.

B2.2.9 (HL) Structure of vesicles - Clathrin

Some vesicles form with the help of a triskelion-shaped coat protein called clathrin. Adaptor proteins recruit C to membrane. C proteins link into a rounded lattice, pulls membrane into a bud. Bud is cleaved by dynamin (protein) to form a vesicle, clathrin architecture disassociates.

B2.2.9 (HL) Receptor-Mediated Endocytosis

Ligand binds to a receptor, which recruits clathrin. Advantage: only the specific ligand internalised, allows greater regulatory control over what enters the cell.