Cell Structure Flashcards
Examples of Prokaryotic cells:
Bacterium
Examples of Eukaryotic cells:
Animal, plant, fungi and protists (algae)
An example of a non eukaryotic/prokaryotic cell
Virus
Organelles within a (prokaryote) bacterium:
- Nucleoid
- Flagellum
- 70s ribosomes
- Chromosomal DNA (plasmids)
- Cell wall
- Cell membrane
- Capsule (peptidoglycan)
- Pili
- Cytoplasm
- Food granule
Organelles within an (eukaryote) animal:
- Nucleus
- Nucleolus
- Nuclear pore
- Nuclear envelope
- Cytoplasm
- Cell membrane
- 80s ribosomes
- Lysosome
- Small multiple vacuoles
- Microtubules
- Golgi apparatus
- Golgi vesicles
- RER
- Smooth ER
- Chromatin
- Centrioles
- Secretory vesicle
- Mitochondria
Organelles within an (eukaryote) plant:
- Nucleus
- Nucleolus
- Nuclear pore
- Nuclear envelope
- Cytoplasm
- Cell membrane
- Cell wall
- 80s ribosomes
- Lysosome
- Large central vacuole
- Vacuole membrane
- Microtubules
- Golgi apparatus
- Golgi vesicles
- RER
- Smooth ER
- Chromatin
- Secretory vesicle
- Mitochondria
- Chlorplast
- Amyloplast (starch grains)
Organelles that only plant cells have and animal cells don’t
Cell wall and chloroplasts
Organelle only animal cells have:
Centrioles
Size (diameter) and DNA arrangement of prokaryotes
1-5um and circular
Size (diameter) and DNA arrangement of eukaryotes
10-100um and linear
Components of the cytoskeleton
Microtubules, intermediate filaments and actin filaments
What is locomotion in a cell?
The ability of cells or organisms to move and propel itself from place to place.
What is the purpose of a cytoskeleton in eukaryotic cells?
Maintains the cell’s shape, and is responsible for the locomotion of the cell itself and the movement of the various organelles
Which part of the cell is responsible for breaking down
used organelles and essentially “digesting” substances?
Lysosomes
What part of the cell allows materials to enter and exit
the cell?
Plasma membrane
When biologists wish to study the internal ultrastructure of cells, they most likely would use…
Transmission electronic microscope
The advantage of light microscopy over electron microscopy is that…
Light microscopy allows one to view dynamic processes in living cells
What is the primary objective of cell fractionation?
To separate the major organelles so that their particular functions can be determined
Large numbers of ribosomes are present in cells that specialize in producing which of the following molecules?
Proteins
Which type of organelle is primarily involved in the synthesis of oils, phospholipids, and steroids?
Smooth endoplasmic reticulum
Which of organelle contains its own DNA and ribosomes?
Mitochondria
Grana, thylakoids, and stroma are all components found in?
Chloroplast
Organelles other than the nucleus that contain DNA include:
Mitochondria and chloroplast
The mitochondrion, like the nucleus, has two or more membrane layers. How is the innermost of these layers
different from that of the nucleus?
The inner mitochondrial membrane is highly folded
Components of a chloroplast
- Envelope (outer membrane)
- Inter-membrane space
- Inner membrane
- Stroma
- Thylakoid system
- Grana
- Peripheral reticulum
Components of a mitochondrion
- Inner membrane
- Outer membrane
- Transmembrane space
- Cristae
- Matrix
- DNA
- Ribosomes
How does chloroplast replicate/reproduce?
Binary fission
How does mitochondria replicate/reproduce?
Simple fission (mitochondrial fission)
Which cell structure would most likely be visible with a light microscope?
Mitochondrion
Which cell would be best for studying lysosomes?
Phagocytic white blood cell
Ions can travel directly from the cytoplasm of one animal cell to the cytoplasm of an adjacent cell through
Gap junctions
What is protoplasm made up of?
Cytoplasm + nucleus + cell membrane
What are cells considered to be?
- the basic units of life
- the building block of all living things
What is the aqueous solution found in the cytoplasm?
Cytosol (approx. 70% of cell volume)
Current cell theory:
- Cells are structural and organizational unit of life
- All living organisms are composed of cells
- All cells come from pre-existing cells
Where are nucleoproteins synthesised?
Cytoplasm
Where are microtubules not found in?
Mitochondria
What are lysosomes rich in?
Hydrolytic enzymes
Polyribosomes are aggregates of?
rRNA
Who was the cell discovered by?
Robert Hooke
Which part of the cell is responsible for breaking down used organelles and essentially “digesting” substances?
Lysosomes
All cells come from pre-existing cells (1858)
Virchow R
All animals are made of cells (1839)
Schwann T
All plants are made of cells (1838)
Schleiden M
First person to observe bacteria (1676) and the sperm cell (1677)
Van Leeuwenhoek A
What is microbiome?
Gut influencing the brain
Ratio of non human cells to human cells
3:1
Describe the DNA of prokaryotes
Naked, circular and usually no introns
Describe the DNA of eukaryotes
Bound to proteins, linear and has introns
Reproduction of prokaryotes and eukaryotes:
- Binary fission
- Mitosis and meiosis
Animal cell and plant cell shape:
- Round or irregular
- Rectangular or cubic
Animal cell size
10-30um
Plant cell size
10-100um
Types of animal cell tissue
- Muscle tissue
- Nervous tissue
- Epithelial tissue
- Connective tissue
Types of muscle cells:
- Skeletal
- Cardiac
- Smooth
Types of neural cells:
- Dentrites
- Axon
Types of epithelial cells:
- Squamous
- Cuboidal
- Columnar
> Simple
Stratified
Visible limits
- Naked eye (10-4m)
- Light microscope (10-7m)
- Electron microscope (10-10m)
Types of microscopy
- Light microscopy (brightfield (visible light) and fluorescent microscopy)
- Electron microscopy (EM)
- Scanning electron microscopy (SEM)
- Transmission electron microscopy (TEM)
Brightfield (visible light)
Essential for cell culture and histology Pros: - Inexpensive - Living cells Cons: - Lack of contrast - Resolution 0.2um - Staining is time consuming
Fluorescence microscopy
Essential for cell biology Pros: - Living cells - Greater contrast - Always improving - 3D
Cons:
- Resolution 0.2um
- Staining is time consuming
- Fairly expensive
Fluorescent markers:
- DAPI (adenine/thymine of DNA, fixed) = blue
- Hoechst 33342 (dsDNA, live and fixed) = blue
- Propidium iodide (PI) = red
Cytoskeleton:
Phalloidin (actin filaments, fixed) - red
Fluorescent proteins:
- Green fluorescent protein (GFP) isolated from jellyfish ‘aqueorea victoria’
- Gene encoding GFP can be fused to any other gene
- When protein is expressed it will be tagged with GFP
- Living cells
Electron Microscopy
> Scanning EM
- Reveals surface topography of sample
- Sample must be coated with an e- absorbent material such as gold
Pros:
- Highest resolution of all - almost atomic level
- Magnification
- Still improving
Cons:
- Very expensive and time consuming
- Specialist knowledge
- 2D (3D very hard)
- Fixed specimens only
- Sensitive to vibration and electromagnetic field (isolated room)
What is cell centrifugation?
Applies strong rotational force, effectively increases the gravitational force on the sample and separates out materials according to their masses
Name the 2 types pf cell culture
Primary cultures and cell lines
Primary cultures
Derived from tissues eg. animals and tissue samples
Pros:
- Real cells = more accurate experiments
Cons:
- Costly: animal use: limited cell numbers
Cell lines
Immortalised cell lineages, can be propagated indefinitely in the lab
Pros:
- Cheap; easy to manipulate; a lot of cells
Cons:
- A model system; may not give true results
How thick is the cell membrane?
8nm thick
Function of the cell membrane
- Selective permeability
- Maintenance of cell integrity
- Transport and cell signalling
Component of the cell membrane:
- Phospholipid bilayer
- Cholesterol
- Carbohydrates
- Proteins
Phospholipid bilayer
Phospholipid bilayers form between aqueous internal and external environments
- Hydrophobic core (tails)
- hydrophilic surface (head)
Cholesterol
- Sterols are present in eukaryotic membranes
- Cholesterol = major sterol in mammalian membrane
- Cholesterol os amphipathic
Fluidity of bilayer: Cholesterol
- Makes lipid bilayer less deformable
- Decreases its permeability to small water soluble molecules
- Prevents phase shifts
- Stops phospholipids packing too tightly at low temp (more fluid)
- Holds phospholipids together at high temp (less fluid)
Membrane carbohydrates
- Generally short and branching
- <15 sugar units
- Covalently bound to lipids (glycolipids) or commonly to proteins (glycoproteins)
- Vary among species, individuals and cell types
- Play a role in cell-cell recognition
- Identification markers
Membrane proteins
- A membrane is a collage of different proteins embedded in the fluid matrix of the lipid bilayer
Types of membrane proteins
- Integrals (transmembrane and partially embedded)
- Peripheral (associated with PL head groups or other integral proteins)
Membrane permeability
- Hydrophobic molecules = eg hydrocarbons, CO2 AND O2 can dissolve in lipid bilayer and pass through the membrane
- Ions, polar molecules (eg. water) and larger molecules (eg. glucose) do not cross the membrane easily. Can be transported across membrane by the aid of membrane proteins
Membrane transporter
- Gradient (internal conc vs external conc)
- Uniporter/antiporter/symporter
What is the cytoskeleton?
Eukaryotic cells are criss-crossed by long filamentous proteins
- Mix of polymers and proteins
Function of the cytoskeleton
- Provide structure = shape, support and organization
- Plays an essential role in cell movement, endocytosis/exocytosis and cell division
Where is the cytoskeleton present?
- Cell cortex
- Cytosol
- Nucleoplasm
What are the components of the cytoskeleton?
- Intermediate filaments
- Actin filaments
- Microtubules
Intermediate filaments:
- Stable, rope like
- Approx 10nm diameter
- High tensile strength
- Strengthen nuclear lamina
- Extend throughput the cytoplasm and nucleus
- Anchored to cell-cell junctions (desmosomes) and cell matrix junctions (hemidesmosomes)
Microtubules:
- Long, hollow tubes
- Relatively stiff
- Extend from the centrosome (near nucleus)
- Cellular scaffols
- Form long tracks throughout the cell
Function of microtubules
- Migration of chromosomes
- Cell movement (flagella/cilia)
- Organelles structure
- Exo/Endocytosis
Structure of microtubules:
- Alpha and beta tubulin dimers
- Dimers stack to form protofilaments
- 13 parallel protofilaments form to hollo microtubules
- 25nm diameter
Centrosome
- The main microtubule organising centre (MTOC)
- Provides anchoring for the microtubule network
- Enriched in y-tubulin rings
- Nucleation site
- Microtubules enxtend from here
- Plus end is away from MTOC
Actin filaments:
- Thin and flexible (helical)
- 5-9nm diameter (7nm)
- Stabilised by actin binding proteins
- Can form permanent structures ( microvilli)
- Polymerisation of globular actin to a chain
- Two chains arranged in a double helix
Motor protein (actin filaments)
Myosin
Extracellular matrix
Part of support tissue for almost all organs and nutrition role
What is the extracellular matrix composed of?
Macroproteins and polysaccharides:
- collagen
- elastin
- proteoglycan
- glycoaminoglycans
- glycoproteins
- growth factors
connective cells/also epithelial cells
Types of cell junctions (epithelial cells)
- Tight junctions
- Adherens junctions
- Gap junctions
Tight junctions
- Ensure cell-cell cohesion at the apical membrane
- Prevent protein diffusion between basal and apical side
Adherens junctions
- Attachment via cytoplasmic plaque (cell belt)
- Maintaining cell shape
- Desmosomes (stud like structures)
Gap junctions
- Juxtapositions of channels for the cell-cell communication
- Channel opening: pH and calcium dependent
What is the endomembrane?
- Series of membrane bound organelles evolved from plasma membrane by invagination
- As cells increased in size, maintains membrane surface area to volume ratio
What is the secretory pathway?
The part of the endomembrane system involved in the synthesis, modification and sorting of secreted proteins and transmembrane protein
What is the secretory made up of?
- Endoplasmic reticulum
- Golgi apparatus
- Secretory and transport vesicles
- Membrane bound organelles
The ER
- A series of hollow tubes, vesicles and sacs (cisternae)
- Extends throughout cell
- Continuous lumen
- Up to 50% of cell’s membrane content
Structure of the endoplasmic reticulum:
- Phospholipid bilayer
- Dense cisternae towards towards cell centre
- Tubules towards periphery
- Extends throughout cell
- Continuous with nuclear envelope
The Rough ER
- Cytoplasmic surface studded with ribosomes
- Site for protein synthesis
Protein translocation
Proteins made by ribosomes on RER are translocated into the ER
Protein translocation process:
- Signal sequence of nascent protein recognised
- Threaded into translocon
- Soluble proteins released in ER lumen
- Transmembrane proteins released sideways into membrane
The Smooth ER
- No ribosomes
- Generally tubular
- Periphery of the cell
Function of the Smooth ER:
- Synthesis of lipids (FA’s) and steroids
- Calcium homeostasis
- Detoxification (liver)
Sarcoplasmic reticulum
- Specialised form of sER
- Found in muscle cells
- Stores and releases CA2+ to trigger contraction
ER exit
- Proteins leave the ER via cop-coated vesicles
- Vesicles moved to the golgi apparatus along microtubules
The golgi apparatus
Series of flattened sacs (cisternae)
- ER side = cis golgi
- Middle = medial golgi
- Cell membrane side = trans golgi
Function of Golgi apparatus:
- Post translational modifications, modification of carbohydrates and addition of new carbohydrates
- Sorting into vesicles for transport
- Plasma membrane endosomes/lysosomes
Secretion via exocytosis
Two forms:
- Constitutive secretion
- Regulated secretion
Constitutive secretion
- Continuous secretion
- Uncontrolled secretion
Examples: - Serum proteins, eg albumin from hepatocytes
- Extracellular matrix proteins, eg collagen from fibroblasts
Regulated secretion
- Proteins are packaged into dense secretory granules
- Granules stored in the cytoplasm
- Released only upon stimulation (hormones and depolarisation)
- Eg, mucus, insulin and neurotransmitters
What is the endocytic pathway?
Part of the endomembrane involved in the internalisation, recycling, and degradation of transmembrane proteins proteins and extracellular materials
What is the endocytic pathway made up of:
- Endocytic vesicles
- Endosomes
- Lysosomes
- Membrane bound compartments
Features of endocytosis:
- Cell membrane is hydrophobic
- Large, polar molecules cannot pass through
Process of endocytosis:
- Pit formation
- Inward budding
- Neck closure
- Vesicle formation
Endosomes
Vesicles move to endosomes
There are 2 major types:
Early endosomes = just beneath the PM
Late endosomes = closer to the nucleus
Early Endosomes (EE)
- Tubulo vesicular
- Protein sorting site
- Returns useful cargo to PM or golgi tubule
- Concentrates cargo for destruction at lysosome (body)
Late Endosomes (LE)
- EE steadily pulled towards the centre
- Once all recyclable cargo is removed, EE matures into late endosome (LE)
- Able to sude with lysosome
- Mediates final sorting and preparation for cargo destruction
Endosomal pH
Endosomes and lysosomes are acidic vesicles (H+ pumps in membrane)
- Sorting of cargo is pH dependent
- Gradient exists through endosomal pathway
- EE pH = 6.0
- LE pH = 5.5
- Lysosome pH = 4.8
Lysosome features:
- Very low pH = 4.8
- Hydrolytic enzymes
- 40 different types
- Includes nucleases, proteases, lipases, glycosidases…
Function of lysosomes:
- Late endosomes fuse with lysosome = degration of contents
- Useful molecules are transported out of lysosome to cytosol
- Lysosome resident TM proteins are highly glycosylated
What are the other forms of endocytosis?
- Receptor mediated endocytosis
- Autophagy
Receptor mediated endocytosis
- Concentrating mechanisms for internalisation
- Via clathrin coated vesicles
- Increased efficiency of uptake (without large EC fluid intake)
Obtaining nutrients:
- Cholesterol, iron
- Terminate signalling
Clathrin
- Vesicle coat protein
- Forms special shape called triskelion (3 heavy chains, 1 or 2 light chains associated with each heavy chain
Autophagy
- Method by which cell’s own contents and organelles are degraded
Endosymbiosis
Primary endosymbiosis refers to the original internalization of prokaryotes by an ancestral eukaryotic cell, resulting in the formation of the mitochondria and chloroplasts
Mitochondria
Found in virtually all eukaryotic cells:
- Animal
- Plants
- Most eukaryotic microorganisms
Specialised site for oxidative phosphorylation
Liver cell’s mitochondria
1000-2000 mitochondria to provide energy to drive chemical reactions
Sperm mitochondria
Many mitochondria wrapped around flagellum to provide energy for movement
Aspects of mitochondria
Contains own circular DNA
- Mitochondrial disease (Leigh syndrome)
- Maternal inheritance
RNA and transcription/translation machinery can make some of their own proteins
Features of the mitochondrion
Contains two membranes: - Outer - Inner Confers 4 distinct compartments: - Matrix - Intermembrane space
Matrix
- Approx 1um wide
Contains highly conc mixture of enzymes
Inner membrane
Folded into numerous cristae
Outer membrane
Contains a large channel-forming protein, porin, the outer membrane is permeable to all molecules of 5000 daltons or less
Inner and Outer membranes
Outer:
- Many transmembrane channel proteins called porins
- Very porus = intermembrane space similar to cytosol
Inner:
- Folded into cristae
- Not porus
- Site of electron transport chain
- ATP synthase embedded in membrane (matrix side)
Mitochondrial matrix
- Concentrated mix 100s of enzymes
- Involved in aerobic respiration which supplies the cell with energy in the form of ATP
- Also concerned with the oxidation of fatty acid molecule
- Site of the citric acid cycle
- The matrix also contains the circular DNA molecules and components for protein synthesis
Features of mitochondria:
- 1um wide
- Two membranes
- Makes ATP
Use of oxygen - Shape varies
- Can form chains
- Own DNA
- Own proteins
- Ribosomes not like eukaryotes
- Binary fission
Features of chloroplasts:
- Double membrane encased organelle
- Found only in plants, algae and some protists
- Site of photosynthesis
- Fixes CO2 to make sugars
- Releases oxygen
- Site of FA synthesis in plants
Thylakoids
Harness light energy to produce ATP and NADPH to power the production of sugars from oxygen
Stromal matrix
House the enzymes necessary to trap CO2 in the form of sugar
Summary of chloroplasts:
- Approx 2um and 1um thick
- Two membranes
- Contains chlorophyll
- Make ATP and sugars (photosynthesis)
- Fix CO2 liberate O2
- Shape varies
- Can form chains
- Own proteins
- Ribosomes not like in eukaryotes
- Binary fission
The nucleus
Two critical functions:
- contains and protects DNA
- coordinates cellular activity
Nucleoplasm - 8-10% total cell volume (inhibition of nuclear export up to 50%) - approx diameter = 5um - absent in red blood cell
In H&E staining what colour is the nuclei?
Purple
The nuclear envelope
2 concentric membranes Inner: - binding of chromosomes - anchors for nuclear lamina Outer: - continuous with ER
Perinuclear space
- Import and export of molecules accomplished via nuclear pore complexes
Nuclear pore complexes (NPC’s)
- large structures - 30 different nucleoporins
- 400-2000 per cell
- Central water filled channel
- Diameter pore = 10nm (uto 25nm)
- Roughly octagonal
- 8 filaments projects into cytoplasm
- 8 filaments project into nucleoplasm = joined to form nuclear basket
Nucleoplasmic transport
Passive transport
- bidirectional
- Can pass freely = water, ions, metabolites (nucleotides) and proteins
Active transport
- Signal sequences
- Nuclear localisation signal (NLS) recognised by importin
- Nuclear export signal (NES) recognised by exportin
Functional units of the nucleus
- Chromatin = DNA and specialised packaging proteins known as histones
- Visible as chromosomes during cell division
Nucleolus
- Non membranous ‘organelle’ within the nucleus
- Contains genes encoding for ribosomal RNA
- Place for synthesis of rRNA and assembly of ribosomes
Ribosomes
- Not strictly a true organelle
- Not membrane bound
- Decode mRNA message into proteins (translation)
- Typical cell has millions of ribosomes
Ribosome function:
Small unit = matches the tRNAs to the mRNA codon
Large unit = catalyses the formation of peptide bonds
Prokaryotic = 50s+30s = 70s Eukaryotic = 60s+40s = 80s
Proteasome
- Not a ‘true’ organelle
- Not membrane bound
- A large macromolecular complex (approx. 50 protein subunits)
- Functions to degrade unwanted protein in the cytosol
Peroxisome
- Membrane bound
- Roughly spherical
- 0.2-1um in diameter
- Rich in enzymes
Peroxisome functions:
- Oxidative break down FAs AA and toxins such as uric acid
- Yield hydrogen peroxide (H2O2)
- contains catalase to breakdown H2O2 to water and oxygen
- Site for synthesis of cholesterol and other metabolites for biosynthetic pathways
- In liver cells = bile acids produced
