Cells Flashcards
what are all organisms made of
All organisms are made of cells
Unicellular organisms have 1 cell. Ex: bacteria, Archaens, many protists
Multicellular organisms have multiple cells, along with tissues and organs in many. Ex: Animals, Plants, Fungi, Some protists
what 5 features do all cells share
All cells share some common features:
- Store genetic information as DNA
- Use ribosomes to make proteins
- Have a plasma membrane
- Use the same building blocks
- Have cytoplasm
how big are cells
Most plant and animal cells are between 10-100 um, while bacteria are between 1-10 um, and some are even smaller.
So to see and study them we need microscopes.
what are light microscopes used for
Light microscopes: down to ~500 nm
can be improved by staining subjects, using phase contrast or differential interference contrast. Using fluorescene can be used to light different parts up in different colours.
what are Electron microscopes used for
Electron microscopy: down to 5nm, used to see cilia or smaller things
2 types: Scanning electron microscopy (3D) or transmission electron microscopy (2D)
Shows black and white, subject needs to be dead.
describe cell fractionation
Take a sample of cells, homogenize by blending, use centrifugation on the homogenate to separate nuclei and cell debris. Then again to separate mitochondria, then microsomes*, then ribosomes. This works by taking the remaining supernatant and centrifuging at a higher speed and longer time to separate smaller components.
*microsomes are small parts of the ER that had been ripped apart
describe prokaryotes
Prokaryotes include the domain bacteria and domain archaea.
Basic cells
On average them are between 1-5 um in size, while the smallest is 0.1 um and the largest is 1 cm long.
why don’t bigger organisms have bigger cells
do larger organisms simply have larger cells?
No, this is because the total surface area increases slower than total volume when increasing the size of a cell.
Surface area determines how much transport can be done into and out of the cell.
Volume determines how many materials are needed. So a big enough cell wouldn’t be able to bring in enough materials to sustain itself.
So the reason larger organisms are bigger is that they have more cells, not bigger cells.
Some cells are big though;
nerve cells get up to 1m long. But they are very thin and so avoid the problem
what do eukaryotes do
Eukaryotes organize their cells into organelles (rooms) via membranes
what are cellular membranes like
These membranes, including the plasma membrane and organelle membranes, are composed of lipids and proteins.
Many membrane proteins (including enzymes) are built into the membrane, they are specific for each membrane.
Carbohydrate side chains are found on the non cytosolic side of the membrane (side with no cytosol, often outside cell or inside organelle).
what do all Eukaryote cells have
- Mitochondria
- Peroxisomes
- Cytoskeleton (microfilament, microtubules, and intermediate filament)
- Golgi apparati
- Nucleus (holds DNA in chromatin, + nucleolus + nuclear membrane)
- Endoplasmic reticulum (rough + small)
what do animal cells uniquely have
- Centrosomes (with centrioles)
- Lysosomes
Other things like microvilli or flagella are optional
Cells all look different though vary a lot even within an organisms
what do plant cells uniquely have
Plant cells specifically have:
- A large central vacuole
- Chloroplast
- Plasmodesmata
- Cell wall (cellulose)
what do fungi uniquely have
Fungi have:
- A chitin cell wall
- Lysosomes
- No chloroplast
describe the nucleus
Holds chromatin: DNA wrapped around proteins.
Surrounded by nuclear membrane/envelope: 2 layers; inner and outer membrane, has nuclear pores for transport
in the interphase chromatin has no defined shape. Before cell division it assembles into chromosomes.
describe ribosomes
Synthesize proteins
In a cell there are millions of ribosomes, found in the cytosol, bound to the ER, or the the outer membrane of the nuclear envelope
They are made from a large and small subunit
describe the ER
Forms cisternae (sacs and tubules), inside is the ER lumen
Continuous with the nuclear envelope
Two parts: the Smooth (no ribosomes) and Rough ER (has ribosomes)
describe the smooth ER
The Smooth ER performs:
- Lipid synthesis
- Detoxification*
- Calcium ion storage
- carbohydrate metabolism (glycogen → glucose)
*Liver cells have a lot of smooth ER, and those of alcoholics have even more
describe the rough ER
The rough ER performs:
- Lipid synthesis
- Protein synthesis for ER, Golgi, lysosomes, plasma membrane, and secretory proteins
- Transport from ER to golgi, lysosome, or plasma membrane via transport vesicles
describe the Golgi
Warehouse of the cell:
- Receiving (cis side), modifying, sorting and shipping (trans side)
- synthesis of macromolecules
- structural directionality: cisternae with different set of enzymes
describe the cellular transport chain
Transport chain:
ER → Transport vesicles → Golgi → 1 or 2
- → membrane (either secreted or used at membrane)
- Lysosome (digested)
describe lysosomes
Digestive compartment, breaks down stuff into basic units
→ Hydrolytic enzyme
→ Acidic pH, so that any enzymes in the more basic cytosol will stop working
Can fuse with food vacuole to digest incoming food from phagocytosis
Used in some cells that take in pathogenic intruders and eat them
Used to recycle damaged organelles. Damaged organelle enclosed in membrane (vesicle) which fuses with lysosome.
describe vacuoles
Variety of vacuoles in unicellular organisms:
- food vacuole after phagocytosis
- Contractile vacuole which pumps water out of cells
Vacuoles in plants:
- Storage for pigments (in petals) and proteins (in seeds)
- Harmful organic compounds for defence against herbivores
- Hydrolytic enzymes as a replacement for lysosome
- Central vacuole for water
describe peroxisomes
Generate H2O2 Hydrogen peroxide
- decompose H2O2 into O2 and H2O
- Involved in lipid catabolism: break chains of fatty acids
- reduction of reactive oxygen species
Special peroxisomes in plant seeds: Glyoxysomes
- Store fat which is converted to sugar in emerging seedling.
describe the Endosymbiont theory
Endosymbiont theory, supported by mitochondria and chloroplast having:
- their own DNA
- own ribosomes (similar to prokaryote ribosomes)
- double membranes
- and being autonomous (divide and not created by cell)
The ancestor of eukaryotic cells (the host cell) engulfed an oxygen using non photosynthetic prokaryote, which over generations became the mitochondria
Then later a non photosynthetic eukaryote engulfed a photosynthetic prokaryote which led to chloroplast. This happened at least once, maybe more time).
describe the mitochondria
- Outer membrane, inter-membrane space, inner membrane with cristae (folds which add surface area)
- Matrix: ribosoms, DNA, and enzymes
In the matrix and inner membrane there are enzymes which catalyze cellular respiration
O2 + Sugar → ATP + CO2 + H2O
describe the chloroplast
- Outer membrane, inter-membrane space, inner membrane
- Stroma: ribosomes, DNA
- Thylakoids: photosynthesis
Light + CO2 + H2O → Sugar + O2
describe plastids
Includes chloroplast
- Chloroplast: green → photosynthesizes
- Amyloplast: colourless → stores starch
- Chromoplast: Yellow/orange → show off pigments in fruits or flowers
what are the three types of molecular structures in the cytoskeleton
Three types of molecular structures:
Microtubules: Hollow tube of stacked tubulin dimers of alpha and beta type. 25 nm wide
Actin filaments: 2 chains of actin subunits wrapped around each other, 7n wide
Intermediate filaments: coiled fibrous subunits made from keratin proteins coiled together. 8-12 nm.
how permanent is the cytoskeleton
Microtubules and Actin filaments are very dynamic, they dismantle and reassemble frequently. Maintain cell shape, mobility of whole cells and organelles (intermediate filaments are more permanent.)
how does cell motility work
- Cytoskeleton interacts with Motor proteins
- Change in cell location
- bend the plasma membrane to form pseudopods
- movement of cell parts → vesicles and organelles more along tracks
a motor protein powered by ATP that attaches to a receptor on a vesicle can “walk” the vesicle along a microtubule or microfilament
What are microtubules, and centrosomes
Composed of alpha and beta tubulin dimers
One end is called the plus end, it is more active with growing and shrinking
In animals the microtubules grow out from the centrioles
Centrosomes are made from 2 centrioles, which are made from 9 triplets of microtubules that form a hollow tube.
how are cilia and flagella made
Microtubules are involved in the formation of flagella and cilia.
Cilia and flagella have a structure made from 9 doublet surrounding 2 long microtubules (9x3 + 2). They are anchored by a basal body, which had a 9x3 + 0 formation of microtubules.
Between the outer microtubules are motor proteins (dyneins) and radial spokes which anchor to the central microtubules.
The whole structure is surrounded by a plasma membrane.
how do flagella and cilia move the cell/other things
Flagella are used for locomotion by unicellular organisms and cells, they undulate to push the cell forward.
Cilia help with the movement of particles and cells. ‘antenna’ are used for signal transduction. Have a power and recovery stroke. Push perpendicular.
describe actin filaments
Support cell shape like microvilli, constantly rebuilding
Used for motility: in muscle contraction myosin beads (attached to myosin filaments) pull actin filaments together to contract a muscle cell.
In cell crawling actin filaments push part of the cell forward to form a pseudopodium
Involved in cytoplasmic streaming to move organelles in the cell
describe intermediate filaments
Only in some animal cells:
more permanent
Stabilize skin, nuclear lamina, keratins
not in insects, spiders, and other hard animals
only squishy ones like us and molluscs.
what are functions of the cell wall in plants
Function:
- cell shape
- prevents excessive water uptake (by confining space cell takes up)
- holds plant body up against gravity
what are the structure of cell walls in plants
- Primary cell wall
- middle lamella (pectin)
- Secondary cell wall (wood)
→ cellulose embedded in matrix of proteins and other polysaccharides
Primary cell wall forms first, then secondary cell wall within it.
Middle lamella is made of pectins, kinda like glue, which holds cell walls together
describe the Extracellular matrix
In animals the main component is collage (which is 40% of the protein in humans) embedded in networks of proteoglycans
Fibronectins connect the collagen fibers to proteins in the cell membrane.
what are plasmodesmata
In plants plasmodesmata connect neighbouring cells through continuous cytoplasm tunnels through the cell wall.
Free passage of water, and small molecules
what are the three cell junction structures in animals
- Tight junctions: neighbouring cells are pressed tightly together to prevent leakage into the Extracellular matrix
- Desmosome: intermediate filaments complex for cell to cell adhesion holds cells together by can stretch
- Gap junctions: cytoplasmic channels which allow exchange of materials
