Organelles Flashcards
What is the Fundamental Difference Between Prokaryotes & Eukaryotes?
The nucleus. Karyon = ‘kernel’ or nucleus.
Describe the subcategory of prokaryotes called eubacteria.
eubacteria
- “true
bacteria”
Eubacteria
- found in
environments familiar to us
Describe the subcategory of prokaryotes called Archea bacteria.
- found in hostile environments as well as in more familiar ones
What are the main features of prokaryotes?
most diverse group of cells successfully inhabit many different environments exhibit many different growth forms
o spherical, rod-shaped, spiral, chains, clusters, organised
multicellular structures
- may be
- organotrophic (use any organic molecule as an energy source)
- phototrophic (use light as an energy source)
- lithotrophic (use inorganic molecules as an energy source)
Stuff to know regarding the differences between eubacteria and archaea.
- Division between these two groups is based on molecular biological characterisations.
They are as different to each other as either is from eukaryotes.
A photo showing the main features of prokaryotes (no.1) (on the other side)
A photo showing the main features of prokaryotes (no.2) (on the other side)
Prokaryotes - Features
“simple” cells
- a few micrometres (um) long
> tough, protective cell wall
- plasma membrane
- essentially no membrane-bound organelles
- have no nucleus
- circular DNA free in cytosol
- ribosomes
- may have a flagellum
- can reproduce quickly, e.g. some divide every 20 min
Eukaryotes two types
> Unicellular
- most protists
- yeast
Multicellular - animals, plants (including multicellular algae) & fungi
Ribosomes
- prokaryotes and eukaryotes
> sites of protein synthesis
- large complexes of
- proteins &
- ribosomal RNAs = rRNAs
> eukaryotic larger (80S) than prokaryotic
(70S)
- two populations in eukaryotes
- cytosolic
- free or attached to Endoplasmic
Reticulum (80S) - in mitochondria & chloroplasts (70S) = bacterial size
Membranes - Composition
- Prokaryotes and eukaryotes
- Bilayer of phospholipids → see L3
- asymmetrical arrangement in the two halves
> Proteins
- integral - embedded in the bilayer
- peripheral - attached loosely to the bilayer
Membranes - Composition photo
Plasma Membrane photo
Membranes
- Selectivity
Selectively permeable
- Small hydrophobic & small uncharged molecules can cross freely.
- Larger uncharged polar molecules & charged solutes must interact with transmembrane proteins (transporters) to cross phospholipid bilayer.
Plasma Membrane
Plasma membrane involved in
- cell signalling transport of solutes
- cell growth & motility
Membranes
- Selectivity photo
Plasma Membrane - Carbohydrate groups
carbohydrate groups attached to lipids - glycolipids , carbohydrate groups attached to proteins - glycoproteins
› on external (non-cytosolic) side of plasma membrane play roles in:
- cell-to-cell communication
- protection from chemical & mechanical damage
Plasma Membrane - Carbohydrate groups photo
Membranes
- Create Compartments
- Compartmentalise cells
- separate cells from their environments
- separate organelles from each other & from the cytosol
- Double membranes surround
- nucleus
- mitochondria
- chloroplasts
Endomembrane system includes….
- Includes: nuclear envelope, ER, Golgi apparatus, transport vesicles, plasma membrane, and endosomes and lysosomes (animal cells) or vacuoles (plant cells)
Endomembrane system photo
structure of eukaryotes and prokaryotes - outcomes
You will be able to
- memorize that cells are the basic unit of life sharing a basic chemistry,
- memorize, identify and contrast characteristics of prokaryotic and eukaryotic cells,
- describe the composition and roles of cellular membranes,
- explain the roles of cellular organelles and compartments,
- explain the origin of mitochondria and chloroplasts - endosymbiosis theory
- describe in detail mitochondrial and chloroplastic structures,
- describe the generation of cellular energy,
- explain the role of proton gradients in ATP production,
- describe the production of carbohydrates in chloroplasts
Endomembrane System:
Golgi Apparatus
➢ stacks of flattened sacs (cisternae)
➢ one or more per cell
➢ synthesis and packaging of molecules to be secreted from cell
➢ routing of newly synthesised proteins to their correct cellular
locations
➢ associated with many transport vesicles
Endomembrane System:
Golgi Apparatus photo
Endomembrane System: Microbodies photo
Golgi Apparatus has
a distinct orientation
cis face - adjacent to ER,
vesicles arrive from the ER
trans face - points toward plasma membrane
➢ transport vesicles pinch off &
fuse with cisternae
➢ carry proteins being modified
by the addition of sugar groups
➢ correlation of enzyme location (e.g. which cisterna) & what step it catalyses in sugar-modification pathway
golgi apparatus cis and trans orientation photo
Endomembrane System: Microbodies
Peroxisomes
▪ single-membrane bound
▪ contain oxidative enzymes
In animals
➢ sites of detoxification (e.g. lots in
liver)
In plants
➢ sites of detoxification
➢ photorespiration (carbon recycling)
➢ conversion of stored fats into
sucrose during germination of
some seeds (= glyoxysomes)
Endomembrane system
– Exocytic Pathway photo
Endomembrane system
– Exocytic Pathway
Membrane growth,
secretion
➢ Outward = exocytic pathway
➢ Proteins synthesised on rough
ER & glycosylated
➢ Vesicles containing glycoproteins
bud off ER & fuse with cis Golgi
cisternae
➢ Glycoproteins are further glycosylated as they travel through Golgi cisternae by vesicle budding & fusion
➢ At the trans face of the Golgi, vesicles are directed to plasma membrane or lysosome/vacuole
Endomembrane system
– Endocytic Pathway photo
Endomembrane system
– Endocytic Pathway
➢ Inward = endocytic pathway
➢ Ingestion & degradation
or recycling) of extracellular molecules
▪ Regions of the plasma membrane containing molecules to be degraded bud inward to form vesicles
▪ Vesicles fuse with early endosomes
▪ Ultimately molecules are degraded in the lysosome /vacuole
▪ Some degradation products can be reused by the cell
Endomembrane System:
Vacuoles
➢ Vacuoles of plant cells are sites of
degradation
➢ They also act as:
▪ storage organs (e.g. seed proteins)
▪ detoxification sites (e.g. tannins)
▪ pigment deposition (e.g. anthocyanins)
Eukaryotes Cells
- Double Membrane bound Organelles
o nucleus – double
membrane
o Mitochondria – double
membrane
o chloroplasts – double
membrane
Endomembrane System:
Vacuoles photo
Nucleus photo
Nucleus
➢ Surrounded by a double
membrane
- continuous with ER
- interrupted by pores
▪ allow passage of selected molecules between cytosol & nucleus
➢ Contains most cellular DNA
- heterochromatin
▪ DNA + proteins - highly condensed, even at interphase
- euchromatin
▪ DNA + proteins - not condensed until mitosis
➢ Typically contains a nucleolus
- site of ribosomal RNA
(rRNA) synthesis & ribosomal subunit assembly
Mitochondria
➢ sites of cellular respiration & major energy (ATP) production
in a process called oxidative phosphorylation
➢ surrounded by a double membrane
▪ smooth outer membrane
❖ permeable to ions & small
molecules
▪ inner membrane
❖ highly folded (into cristae)
❖ impermeable
❖ transport proteins control substrate movement across the inner membrane
❖ contains an electron transport chain & ATP synthase
Chloroplasts
– Thylakoids and Lumen
Thylakoids
▪ formed by a folded internal membrane system
▪ folded into stacks – grana
➢ light-harvesting pigments
➢ electron transport chain
➢ ATP synthase Lumen
➢ space between thylakoids
Mitochondria photo
Mitochondrial Matrix
➢ Region not taken up by membranes
➢ Contains:
▪ DNA ➔ mitochondrial genome
❖ codes for
o mitochondrial tRNA
o mitochondrial rRNA
o mitochondrial mRNA
- proteins for DNA synthesis & oxidative reactions
▪ Mitochondrial ribosomes (70S)
▪ Enzymes for the tricarboxylic acid (citric acid, Krebs) cycle
Chloroplasts – Organelle with a double membrane
➢ sites of photosynthesis
❖ two sets of reactions:
▪ light harvesting
▪ carbohydrate production
➢ surrounded by a double membrane:
❖ outer membrane
▪ permeable to ions & small molecules
❖ inner membrane
▪ impermeable
▪ transport proteins control movement of substrates across internal membrane system
Chloroplasts photo
Chloroplasts
– Thylakoids and Lumen photo 1
Chloroplasts
– Thylakoids and Lumen photo 2
Chloroplasts - Stroma
➢ region not taken up by thylakoid membranes
➢ contains
❖ DNA codes for
▪ tRNA
▪ rRNA
▪ mRNA ➔ proteins for DNA synthesis & photosynthesis
❖ ribosomes (70S)
❖ enzymes for carbohydrate production
Chloroplasts - Stroma photo
Mitochondria & Chloroplasts
are Products of Endosymbiosis
- An ancestral eukaryotic cell ingested, but did not digest an aerobic bacterium, which over time evolved into a mitochondrion. ➔ eukaryotic cells
- Eukaryotic cells later ingested a photosynthetic bacterium without
digesting it.
Over time, this ingested bacterial cell evolved into a chloroplast ➔ plant cells
Mitochondria & Chloroplasts
are Products of Endosymbiosis photo
Energy Production Overview
➢ Digestive enzymes breakdown:
- proteins to amino acids
- polysaccharides to simple sugars
- fats to fatty acids & glycerol
➢ Breakdown products enter cell
cytosol for gradual oxidation & production of some energy (ATP) and reducing molecules (NADH)
➢ The final stages and the majority of energy production takes place in the mitochondria.
Energy Production Overview photo
Cytosol Energy Production: Early Stages
CYTOSOL:
➢ Glucose & other sugars are converted to pyruvate through
glycolysis.
➢ This generates some energy molecules (ATP, NADH)
➢ Some amino acids are converted to pyruvate.
Mitochondria
Energy Production: Early Stages
➢ Pyruvate, some amino acids and fatty acids enter the
mitochondrion.
➢ Pyruvate, fatty acids and some amino acids are oxidised
to acetyl CoA in the mitochondrion.
Mitochondria
Production of Reducing Molecules photo
Mitochondria
Energy Production: Early Stages photo
Cytosol Energy Production: Early Stages photo
Mitochondria
Production of Reducing Molecules
➢ Acetyl CoA is further oxidised by
the citric acid cycle
Produces:
- CO2
diffuses out of
mitochondria via membranes
o NADH & FADH2
(FADH2 not shown)
o NADH and FADH2 are
molecules with strong
reducing power
Note: some amino acids can enter
the citric acid cycle at intermediate
steps & be oxidised directly
Electron Transport Chain (ETC)
Using reducing power to generate ATP - overview
➢ NADH & FADH2 have strong
reducing power = ‘high energy
electrons’
➢ NADH & FADH2 donate
electrons to electron transport
chain (ETC) in the inner
mitochondrial membrane.
➢ The electrons move through the
electron transport chain ➔
consist of multiprotein
complexes
➢ This results in:
▪ oxidation of NADH & FADH2
▪ reduction of O2
to H2O
▪ ATP production.
Electron Transport Chain (ETC)
Using reducing power to generate ATP - overview photo
Mitochondria – Finally, ATP production
➢ Pumping of electrons leads to a H+
(proton) gradient
▪ higher concentration of protons in the inter membrane space than in the
matrix
➢ ATP is synthesised as protons move through the ATP synthase from the inter membrane space into the matrix.
➢ ATP is transported out of the mitochondrion for use by the cell.
Mitochondria – Finally, ATP production photo
Chloroplasts
– Light Harvesting Reaction
➢ Light energy is collected by pigments in the thylakoid membranes
➢ Converted to reducing power (NADPH) and chemical energy (ATP) via a series of oxidation-reduction reactions
➢ H2O being the original electron donor and NADPH the final electron acceptor.
Chloroplasts
– Light Harvesting Reaction photo
The Chloroplast
- Electron Transport Chain
➢ During electron transport, protons move across the thylakoid membranes from the stroma into the thylakoid lumen, generating a proton gradient.
➢ ATP is synthesised as protons move back across the membrane, from the thylakoid lumen into the stroma, through the chloroplastic ATP synthase.
The Chloroplast
- Electron Transport Chain photo
Carbohydrate Production
in the Chloroplast
➢ Calvin cycle uses NADPH & ATP produced during the light reactions
for the synthesis of carbohydrates from atmospheric CO2 in the stroma.
➢ The enzyme Rubisco = ribulose 1,5-bisphosphate carboxylase/oxygenase catalyses the first reaction in the Calvin cycle
➢ Rubisco is the most abundant enzyme in the world.
Carbohydrate Production
in the Chloroplast photo
Cytoskeleton
- Overview
➢ complex, dynamic network of
interlinking protein filaments present
in the cytoplasm of all cells, including those of eukaryotes, bacteria and archaea.
➢ Functions: support, shape, motility,
intracellular transport, chromosome movement, cell division
➢ dynamic - continuously reorganised
➢ three types of components - each
formed from protein subunits
▪ actin filaments –
microfilaments
▪ intermediate filaments
▪ microtubules
Cytoskeleton
- Overview photo
Cytoskeleton
- Actin Filaments
➢ Also known as microfilaments
➢ found in all eukaryotic cells
Structure:
▪ composed of linear polymers made up of globular (G-) actin subunits
▪ G-actin monomers combine form a polymer which continues to form the actin filament (7 nm diameter). Two chains intertwine to from an F-actin(Filamentous actin) chain.
▪ cross-linked into bundles & networks
➢ maintenance of eukaryotic cell shape, cell movement, cell division, muscle contraction, intracellular transport and vesicular movement
➢ actin rearrangements within cells is the molecular basis for changes in cell shape & movement
Cytoskeleton
- Actin Filaments photo
Cytoskeleton
- Intermediate Filaments photo
Cytoskeleton
- Intermediate Filaments
Actin 7nm < intermediate 10nm < microtubules 25nm
Found in:
➢ Cytoplasm and nuclear lamin of vertebrates, and many invertebrates Structure:
➢ subunits = heterogeneous family of proteins collectively called intermediate proteins
➢ Two proteins twisted together into an alpha helical dimer. Two dimers form a tetramer. Many tetramers
form a rope-like intermediate filament.
➢ Example: keratin filaments
Functions:
➢ strengthens the cytoskeleton and nuclear envelope
➢ attachment sites for chromatin
➢ anchoring organelles
➢ protein movement
Can you …
- … state characteristics of cells and their basic chemistry and life?
- … differentiate between archae- and eubacteria, describe features
and give examples? - … describe similarities and differences between prokaryotic and
eukaryotic cells? - … explain features/structures and roles of ribosomes, membranes
and organelles? - … explain a model for the origin of mitochondria and plastids?
- … explain key metabolic processes in mitochondria and chloroplasts
related to energy production and carbon metabolism? - … describe components of the cytoskeleton and give examples for
their roles?
Cytoskeleton
– Microtubules
Found in all eukaryotic cells
Structure
➢subunits = tubulin - dimers of - &
*- tubulin
➢dimers stack into filaments, which
form walls of stiff hollow tubes (25
nm in diameter)
Function
➢ Maintenance of cell structure
➢ intracellular organisation & transport, mitosis, internal structure of cilia & flagella
➢ Main constituents of mitotic spindles
Location
➢ extend from an organising structure, e.g. centrosome, spindle
pole, basal body
Cytoskeleton
– Microtubules photo
