Prokaryotes and Eukaryotes Flashcards
Describe eukaryotic cells
- has a true nucleus
- multi-cellular organisms
- membrane-bound organelles
- cells are usually larger
Describe prokaryotic cells
- do not contain a nucleus
- no membrane-bound organelles
- circular DNA and plasmids
- unicellular (e.g. bacteria)
Describe the differences between prokaryotic and eukaryotic DNA
Eukaryotic: • very long • linear • associated eith histones • no introns • contain DNA in chloroplasts/mitochondria which is single-stranded and much shorter
Prokaryotic: • short • circular DNA and plasmids • not associated with protein molecules • contain introns
Why do mitochondria and chloroplasts need their own DNA that resembles that of prokaryotes?
They need a constant supply of proteins
Describe the similarities between eukaryotics and prokaryotes
- both nucleotides joined by the phosphodiester bonds
* nucleotide structures are identical
Describe compartmentalisation
- each cell has organelles which all have different specialised functions
- important for different reactions and processes to take place
- divides long tasks into smaller ones to be completed in sections
- AKA: ‘division of labour’
List the organelles bound by a single membrane
1) smooth endoplasmic reticulum
2) rough endoplasmic reticulum
3) Golgi apparatus
4) vesicles
5) vacuole
6) lysosomes
List the organelles bound by an envelope
- nucleus
- mitochondria
- chloroplast
What is an envelope
A double membrane
List the non-membrane bound organelles:
- ribosomes (70s, 80s)
- centrioles
- microtubules
- microfilaments
- cilia and flagella
Describe the nucleus:
- largest organelle
- enclosed in a nuclear envelope perforated by nuclear pores
- contains chromatin
- contains one or more nucleoli
- continuous with endoplasmic reticulum
- usually only one, but there can be multiple in very large cells (e.g. striated); multinucleated cells are called coenocytes
Describe chromatin
- DNA wound around fibrous histone proteins
* coils and condenses to form chromosomes (which control protein synthesis)
Describe nucleoli
- darkly stained
* where ribosome subunits, ribosomal RNA and tRNA are manufactured
Define DNA
inherited material which controls the various activities within the cell
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What is the function of the nuclear pores?
Control the exchange of materials between the nucleus and the cytoplasm
Describe euchromatin
- stains lightly
* thought to contain active DNA
Describe heterochromatin
- stains deeply
* thought to contain inactive DNA
Describe the smooth endoplasmic reticulum
- made up of cisternae forming tubes and sheets
- essential lipids, steroids, carbohydrates and other non-protein products are synthesised and secreted here
- SER of liver cells contain enzymes which down many chemicals
What are cisternae?
Flattened membrane bound sacks filled with fluid
Describe the rough endoplasmic reticulum
- made up of cisternae
- membrane on cytoplasmic side is lined with ribosomes which attach to the surface and are the site of protein synthesis and manufacture extracellular enzymes; NOTE: not all ribsomes are here- some are not membrane-bound and float in the cytoplasm, manufacturing intraceullar enzymes as there is no way of performing exocytosis to remove them
- forms a system of channels for transporting materials through the cytoplasm
- the intracellular membrane system aids cell compartmentalisation; stores and prepares proteins for secretion and packages the RER vesicles synthesised on the ribosomes with some of its own membrane, then transports them to the Golgi apparatus
Describe the Golgi apparatus
- made up of cisternae
- new membrane is continually added to one end and buds off as vesicles at the other end
- modified RER vesicles and other cell products delivered to it, often adding carbohydrates to form glycoproteins
- prepares modified RER vesicles for secretion by enclosing them in vesicles
- involved in formation of lysosomes
Describe the differences of the Golgi apparatus between animal and plant cells
animal -> forms an extensive network. Involved in lipid modification in ileum cells
plant -> better defined, called dicytosome. Synthesises polysaccharides and packages them in vesicles which migrate to the cell membrane for eventual incorporation into the cell wall
Describe vesicles
- carry substances around cells
- carries synthetic products of cells or products of degradation by lysosomes
- abundant in cells with high synthetic activity
Describe secretory vesicles
- undergo exocytosis
- e.g. proteins packaged at the Golgi apparatus
- e.g. cells of the Islets of Langerhans
Describe endocytic vesicles
May contain molecules to large to cross the membrane by active transport or diffusion
Describe the peroxisome
- one of the groups of vesicles known as microbodies
- each of them contains oxidative enzymes (e.g. catalase)
- particularly important in delaying cell ageing
Describe the vacuole
- a sac bounded by the tonoplast
- contains cell sap, water and waste products, enzymes (involved in recycling on cell components [e.g. chloroplasts])
- changes in volume affect the turgidity of the cell; maintains turgour pressure
What is the tonoplast
The single membrane surrounding the vacuole
What is cell sap
A solution of pigments, organic acids, salts, sugars and other solutes
What are arythrocyanins?
Pigments responsible for many of the red, blue and purple colours of flowers
Describe mitochondria
- cigar-shaped, rod-like
- small (1-2μm long)
- surrounded by an envelope
- inner membrane highly folded to form cristae, supports the enzymes of the electron transport chain
- watery matrix contains enzymes for the TCA cycle, a circular DNA molecule, ribosomes and calcium phosphate granules
- site of aerobic respiration, responsible for generation of majority of cells’ ATP
What are cristae?
Deep folds that form shelves in the inner membrane of the mitochondria
What do the enzymes of the electron transfer chain do?
Synthesise ATP by oxidative phosphorylation
What is the TCA cycle?
An important ‘metabolic hub’
Where are mitochondria abundant in animal cells?
- skeletal muscle because it is physically active
* hepatocytes because they are metabolically active
Where are mitochondria abundant in plant cells?
Sieve tube companion cells, root epidermal cells and dividing meristematic cells
Describe chloroplasts
- large (5-10μm)
- occur only in green parts of the plant; absent from underground structures like roots
- found in plants and algae
- 3 membrane system; envelope + internal membrane system
- contains stroma
- site of photosynthesis (contains the pigments used in the reactions)
What are the green parts of a plant?
The parts that have been exposed to light
What is the stroma?
- gel-like chloroplast matrix
- contains grana, circular DNA (non-membrane bound), 70s ribosomes and photosynthetic enzymes
- stores lipid droplets and starch grains
Describe grana
- stacks of internal membrane system in the stroma of a chloroplast
- thylakoids contain chlorophyll and other photosynthetic pigments
How does photosynthesis take place?
Pigments capture the energy of sunlight and transfer it to chemical bonds
Chlorophyll absorbs light energy to make chemical energy in the form of glucose
Describe thylakoids
- individual stacks of internal membrane system that form the grana as a collective; located in the stroma of a chloroplast
- increase SA
What is chlorophyll?
The main photosynthetic pigment; it is green
Endosymbiotic theory
Chloroplasts and mitochondria used to be functioning cells that were absorbed by eukaryotic cells and became organelles
Plastids
All develop from proplastids
Proplastids
- small organelles
* pale green/colourless
Describe chromoplasts
- another tropical plastid of complex cells
- many develop from chloroplasts by internal rearrangements
- coloured due to presence of carotenoid pigments
- most abondant in cells of flower petals or fruit skins
Leucoplasts
- another typical plastid of higher plant cells
- e.g. amyloplasts -> synthesise and store starches
- e.g. elaioplasts -> synthesise oils
Describe ribosomes
- v. Small
- not membrane-bound
- made up of a large and small sub-unit
- made of protein and RNA
- uses nucleic acid into for protein synthesis (principally for intracellular protein)
- 50,000 or more
- on RER and cytoplasm
Lysozomes
- contain digestive enzymes that break down extracellular proteins
- eliminate worn-out mitochondria and other redundant organelles
- digest the contents of vacuoles ingested by white blood cells
- involved in autolysis and apoptosis
- e.g. acrozome -> in the head of sperm, hydrolytic enzymes digest the outside of the egg
autolysis
The process by which a cell self-destructs when it dies or is injured
Apoptosis
Involves a genetically programmed series of biochemical events that leads to cell death; occurs during the normal development of multicellular organisms
Centrioles
- a pair of short cylinders made up of 9 protein fibres -> microtubules
- held at right angles
- organisers of the nuclear spindle in preparation for the separation of chromosomes or chromatids during nuclear division
- Make the spindle fibres
Microfilaments
- threads of actin
- usually situated in bundles just below fell surface
- role in bulk transport and cell motility; move against each other
Actin
- protein
* similar to muscle cells
Cytoskeleton
- network of protein fibres
- gives structure and shape
- moves organelles around cell
Microtubules
- made of tubulin, hollow
- involved in intracellular transport
- structural role (part of cytoskeleton)
- components include other specialised structures (centrioles, basal bodies of cilia and flagella)
- in plants -> occur just below cell membrane where they may aid the addition of cellulose to the cell wall
- involved in cytoplasmic streaming of organelles (e.g. Golgi bodies and chloroplasts)
- from the spindles and cell plates of dividing cells
Tubulin
A protein
Intracellular transport
- movement of mitochondria
- movement of vesicles from ER to Golgi apparatus
- can move a microorganism through a liquid
- move chromosomes during mitosis
Flagella and cilia
- flagella -> AKA. undulipodia
- contain 9 microtubules in a cylinder + 1 in the centre
- difference: cilia are shorter, there are more of them
- flagellin -> bacteria’s ‘true motor’
- e.g. sperm tell, bacteria, cilia in throat
Cell membrane
- plasmalemma, plasmamembrane
- 7-10nm thick
- can be seen under e- microscope
- many specialisations, often concerning protein content
- represents contact of cell with its environment
- phospholipid bilayer with intrinsic and extrinsic protein molecules
- partially permeable barrier which controls the passage of substances into and out of the cell; regulates movement of solutes between the cell and its environment
- involved in cell recognition and signalling
- microvilli
- in plants -> flexible enough to move towards or away from the cell wall as cytoplasm water potential changes
- responsible for the synthesis and assembly of cell wall components
Phospholipid bilayer
- hydrophobic and hydrophilic properties - gives the bilayer some stability
- separates cell contents from outside environment
- lots of lateral movement across the monolayer, infrequent ‘flip flop’ movement
Fluid mosaic model
- phospholipid bilayer
- channel protein
- carrier protein
- glycolipid
- glycoprotein
- extrinsic protein
- actin microfilament
- cholesterol
Prokaryote
- bacteria
- cell membrane
- cell wall
- 70s ribosomes (because they are not membrane-bound)
- bacterial chromosome, circular DNA (no nucleus or nuclear envelope)
- plasmids
- mesosomes
- flagella
- vacuole
- cytoskeleton
- slime capsule
- no chloroplasts, only bacterial chlorophyll associated with cell membrane in some so that they can photosynthesis, because chloroplasts are membrane-bound
Prokaryotic cell wall
- made of peptidoglycan (murein)
* Barrier which excludes certain substances and prevents osmotic lysis
Plasmids function
Hold genes that can help the bacteria survive in harsh conditions, such as the gene to produce enzymes that break down …
Mesosomes
Where ATP is made
Because there are no mitochondria?
Flagella
Made of flagellin
Slime capsule function
- protects bacteria from other cells and sticks groups of bacteria together
- not always present
- mucilaginous
Eukaryotes vs. Prokaryotes
- distinct nucleus, nuclear envelope vs. no true nucleus, only an area where DNA is found
- histones, DNA is associated with proteins vs. no histones, DNA is not associated with proteins
- linear DNA (no plasmids) vs. Circular DNA (plasmids)
- membrane-bound organelles vs. None
- chloroplasts is plants and algae vs. None
- 80s and 70s ribosomes vs. 70s ribosomes
- cell walls of cellulose or chitin vs. murein
- no capsule vs. May contain one
Centrifugation
1) tissue chilled and cut into pieces in cold, isotonic, buffered solution
2) tissue homogenised in a pestle homogeniser or a blender to break open cells and release organelles
3) homogenised suspension filtered
4) filtrate centrifuged at a low speed to remove debris and partially opened cells
5) supernatant containing organelles decanted off carefully
Option 1: density gradient centrifugation
6) supernatant pipettes carefully onto sucrose solution
7) density gradient formed by different concentrations of sucrose solution
8) tube containing organelles in density gradient sucrose solution is centrifuged
9) organelles settle out according to their density at a specific level in the centrifuge tube
Density gradient centrifugation order
From top to bottom:
1) ribosomes
2) mitochondria
3) chloroplasts
4) nucleus
5) cell debris
Hole pierced in bottom of tube so that different organelles can be collected in separate tubes
Option 2: differential centrifugation
6) supernatant containing organelles is centrifuged at 500-600g for 5-10mins, producing a sediment rich in nuclei and the new supernatant
7) supernatant centrifuged at 10,000-20,000g got 15-20mins, producing a sédiment containing lysozomes and mitochondria and the new supernatant
8) supernatant centrifuged at 100,000g for 60mins, producing a sediment containing fragments of ribosomes and endoplasmic reticulum
