Cells Flashcards
Cells
Smallest functional unit of an organism. Either prokaryotic or eukaryotic
Domains of Life
Cells are classified as belonging to distinct domains or phyla (bacteria, archaea and eukaryotes) that are all thought to have evolved from a common ancestor cell
Cell Theory
- Every living organism is made up of one or more cells.
- The smallest living organisms are single cells, and cells are the functional units of multicellular organisms.
- All cells arise from preexisting cells.
Cell Shapes and Sizes
About 200 types of cells in human body with varied shapes:
Squamous—thin, flat, scaly
Cuboidal—squarish-looking
Columnar—taller than wide
Polygonal—irregularly angular shapes, multiple sides
Stellate—star-like
Spheroid to ovoid—round to oval
Discoidal—disc-shaped
Fusiform—thick in middle, tapered toward the ends
Fibrous—thread-like
Note: A cell’s shape can appear different if viewed in a different type of section (longitudinal versus cross section)
Common Cells Shapes
squamous
cuboidal
columnar
polygonal
stellate
spheroidal
discoidal
fusiform (spindle-shaped)
fibrous
Typical size of cell in human body
about 20 micrometers
Definition of cell
Bounded by a PHOSPHOLIPID BILAYER (aka the plasma membrane) that separates the cytoplasm from the extracellular environment.
Gathers raw materials from the environment and uses it as structural building blocks and as a source of free energy that is used to create and maintain its organization.
Contains a heritable genetic code that encodes proteins. (RNA or DNA)
Can divide and reproduce itself (not all can divide).
Basic Components of a Cell
1) Plasma (cell) membrane -
Surrounds cell, defines boundaries
Made of proteins and lipids
2) Cytoplasm -
Cytosol (intracellular fluid, ICF)
Organelles
Cytoskeleton
Inclusions (stored or foreign particles)
3) Extracellular fluid (ECF) -
Fluid outside of cells includes tissue (interstitial) fluid
Plasma Membrane
The border of the cell -
Appears as pair of dark parallel lines when viewed with electron microscope
Has intracellular and extracellular faces
Functions -
Defines cell boundaries
Governs interactions with other cells
Controls passage of materials in and out of cell
Plasma Membrane Composition
98% of membrane molecules are lipids and 2% of molecules are proteins
made of membrane lipids and membrane proteins
Membrane Lipids
Phospholipids
75% of membrane lipids are phospholipids
Amphipathic molecules arranged in a bilayer
Cholesterol
20% of the membrane lipids
Holds phospholipids still and can stiffen membrane
Glycolipids
5% of the membrane lipids
Phospholipids with short carbohydrate chains on extracellular face
Contributes to glycocalyx—carbohydrate coating on cell surface
Membrane Proteins
They may only be 2% of the molecules present, but they are 50% of the weight of the membrane
Phospholipids
75% of membrane lipids are phospholipids
Amphipathic molecules arranged in a bilayer
2 monolayers (sometimes called ‘leaflets’) make a bilayer.
Phospholipid Distribution
Distribution of the different lipids in the bilayer are not even
Phosphatidylserine (green) (has a negative charge) & Phosphatidylethanolamine (yellow) are concentrated within the cytosolic monolayer.
Phosphatidylcholine (red) & Sphingomyelin (brown) are concentrated within the extracellular monolayer.
Glycolipids (blue) are confined to the extracellular monolayer.
Top (extracellular monolayer) is red, brown, red, brown on and on and then blue on top some parts
bottom (cystolic monolayer) is mainly yellow and green with some brown and red
Plasma Membrane Fluidity
Fluid mosaic
Unsaturated hydrocarbon tails (kinked) prevent packing, enhacing membrane fluidity
Extensions of the cell surface - Microvilli
Finger-like projections from cell surface
- Extensions of membrane (1 to 2 μm)
- Gives 15 to 40 times more surface area
- Best developed in cells specialized in absorption
On some absorptive cells they
are very dense and appear as a
fringe—“brush border”
maximizes contact so we can absorb as much as we can
Extensions of the Cell surface - Primary Cilium
Single, non-motile primary cilium found on nearly every cell
* “Antenna” for monitoring nearby conditions (they have a sensory function)
* Helps with balance in inner ear; light detection in retina
Extensions of the cell surface - motile cilia
Hair-like structures filled with microtubules and proteins
- 50-200 on each cell that has them
- beat in coordinated fashion (in unison)
move like your arms doing the
breast stroke - move mucus layer across cell surface
- found in respiratory tract, uterine tubes, ventricles of brain, ducts of testes
Cilia beat freely within a saline layer at cell surface
*Chloride pumps pump Cl− into
ECF
* Na+ and H2O follow
Mucus floats on top of saline layer
flagella
long, whip-like structures
-found only in one cell in humans (sperm)
-used for swimming
-beat using a sinusoidal wave
Pseudopods
Pseudopods are continually changing extensions of the cell that vary in shape and size
-Can be used for cellular
locomotion, capturing foreign
particles
Intracellular bilayers
The majority of a cell’s phospholipid bilayers are intracellular
Cytoplasm
A cell’s cytoplasm is the space between the nucleus and the plasma membrane. It is composed of organelles and the cytosol.
Cytosol
liquid portion of the cytoplasm
organelles
“little organs” with are distinct intracellular compartments with specific functions
Membranous organelles
Nucleus, mitochondria, lysosomes, peroxisomes, endoplasmic reticulum, and Golgi complex
Non-membranous organelles
Ribosomes, centrosomes, centrioles, proteasomes, basal bodies
Nucleus
Enclosed by two phospholipid bilayers that are perforated by nuclear pores. Houses genetic material.
- Usually the largest organelle.
- Most cells have one nucleus, but some are anucleate (mature RBCs) and some are multinucleate (muscle cells)
- Nucleolus is where synthesis of ribosomes occur
Nucleolus
is where synthesis of ribosomes occur
Nucleus and Transcription
Normally, chromatin is not as tightly condensed as it can be (chromosomes are only in that X shape during cell division). This leaves the DNA accessible to molecules involved in transcription.
Endoplasmic Reticulum
Rough and smooth ER are functionally different parts of the same network
Smooth Endoplasmic Reticulum
- Enclosed by a single phospholipid bilayer.
- Lacks ribosomes
- Cisterns more tubular and branching
- Synthesizes new lipids
- Detoxifies alcohol and other drugs
- sequesters & releases Ca2+ ions.
Rough Endoplasmic Reticulum
Enclosed by a single phospholipid bilayer. Parallel, flattened sacs covered with ribosomes.
Continuous with outer membrane of nuclear envelope, a very large organelle!
Synthesizes proteins that are packaged in other organelles or secreted from cell
Ribosomes
Not enclosed by a lipid bilayer. They are small granules of protein and RNA
-Found in nucleoli, in cytosol, and on outer surfaces of rough ER, and nuclear envelope
They “read” coded genetic messages (messenger RNA) and assemble amino acids into proteins specified by the code
Ribosomes & Rough ER (RER)
Some proteins will start being created in the cytosol, but need to end up somewhere else. Proteins have tags that ensure they get delivered to where they need to end up. Some may go to the Rough Endoplasmic Reticulum (RER), some may stay in the cytosol, and some may even go to the mitochondria, peroxisomes, and nucleus.
If it has a tag for the Rough Endoplasmic Reticulum, it will head there to be processed (CO-TRANSLATIONAL TRANSLOCATION as shown above) or some will be relocated after translation finishes (POST-TRANSLATIONAL TRANSLOCATION).
Golgi Apparatus
post office of the cell
Enclosed by a single phospholipid bilayer. This complex is a system of cisterns that synthesizes carbohydrates and puts finishing touches on protein synthesis
-Sorts, tags, packages, and
distributes the proteins and
lipids from the endoplasmic
reticulum. Think of it as a
post office or distribution
warehouse.
Receives newly synthesized proteins from rough ER
Sorts proteins, splices some, adds carbohydrate moieties to some, and packages them into membrane-bound Golgi vesicles
Mitochondria
Enclosed by two phospholipid bilayers. Organelles specialized for synthesizing ATP, and it also stores Ca2+ ions.
Surrounded by a double membrane
-Inner membrane has folds
called cristae
-Spaces between cristae called
-matrix
-Matrix contains ribosomes, enzymes used for ATP synthesis, small circular DNA molecule
-Multiple molecules of mitochondrial DNA (mtDNA)
Considered an endosymbiotic organelle
Endosymbiotic Theory History
Mitochondria (& chloroplasts) are thought to be the descendants of previously free-living prokaryotic cells.
Mitochondria (and chloroplasts) are thought to have originally entered ancestral eukaryotic host cell via endocytosis.
Endosymbiotic Theory
- Mitochondria possess their own DNA and ribosomes.
- The mitochondrial genome only encodes 37 genes.
- Mitochondria obtain 99% of their proteins from genes located within the ‘host’ cell nucleus.
- Mitochondria self-reproduce by dividing within our cells (their division is somewhat autonomous).
Lysosomes
Enclosed by single phospholipid bilayer. It contains hydrolytic enzymes that will digest endocytosed materials.
- digest proteins, sugars, lipids, nucleic acids
- The “garbage disposals” of cells
- Very important in immunity, too!
- Involved in autophagy.
Peroxisomes
Enclosed by single phospholipid bilayer. Peroxisomes resemble lysosomes but contain different enzymes and are produced by endoplasmic reticulum.
- Use molecular oxygen to oxidize organic molecules
- Creates and destroys hydrogen peroxide.
- Neutralizes toxic compounds.
- Synthesizes plasmalogen phospholipids found in the myelin coating of neuronal axons.
Proteasomes
Not enclosed by a lipid bilayer
Hollow, cylindrical organelle that disposes of surplus proteins
-Contain enzymes that break
down tagged, targeted
proteins into short peptides
Centrioles and Centrosomes
Not enclosed by a lipid bilayer. Centrioles are a short cylindrical assembly of microtubules.
Two centrioles lie perpendicular to each other within the centrosome—small clear area in cell
-Play important role in cell
division
-Form basal bodies of cilia
and flagella
Cytoskeleton
Not enclosed by a lipid bilayer
*Provides scaffolding for maintaining cell shape.
*Enables contraction of many cell types.
*Provides tracks for molecular motors to run along.
*Enables chromosome separation at mitosis.
Inclusions
These are not enclosed by a lipid bilayer. They can contain stored cellular products and foreign bodies phagocytized by the cell. They are not essential for cell survival
Examples:
glycogen granules
fat droplets
melanin pigment granules
ribosomes
globs of various materials
proteasomes
Organelles interaction
Organelles work together to create a properly functioning cell. A good example of this is how cells make and process proteins.
Insulin production uses mRNA copy of the gene, leaves nucleus to attach to a ribosome in the ER and reads the instructions to assemble protein (insulin). The insulin molecules are pinched off in vesicles and travel towards the Golgi apparatus to fuse with it and gets processed and packaged for release. The packaged insulin molecules are “pinched off” in vesicles from Golgi apparatus and move towards cell surface membrane. The vesicle then fuses with cell surface membrane and cell surface membrane opens to release insulin molecules outside.
When things go wrong
Golgi apparatus
-Alzheimer’s
-CDG syndrome
Endoplasmic reticulum:
-cystic fibrosis
-ERSDs
Nuclear envelope
-Progeria
-ED muscular dystrophy
Lysosomes related organelles
-LSD (Tay-Sachs disease)
-Autoimmune diseases
Mitochondria
-Cardiomyopathy
-Cancer
-Diabetes mellitus and deafness
Plasma membrane
-Familial hypercholesterolemia
Infectious diseases (HIV, shigella, etc.)
Kartagener syndrom
Defective dynein (motor protein in cilia) make cilia unable to beat properly. Cilia in embryonic cells help determine symmetry in development. Defective cilia lead to situs inversus, respiratory issues, and even infertility.
Mutations that lead to ER : Cystic Fibrosis
There are a number of mutations that can lead to cystic fibrosis.
- Most mutations will generate a protein that is unable to leave the ER.
- The ER has strict control mechanisms that prevents incorrectly folded proteins from leaving.
- CF mutations can generate functional proteins that are only slightly misfolded (slightly bent the wrong way).
- The ER will not let these proteins leave and degrade them. These proteins make the Cl- channels needed in the membrane
Cystic Fibrosis
Hereditary disease in which chloride pumps fail to create adequate saline layer on cell surface
Thick mucus plugs pancreatic ducts and respiratory tract
*Inadequate digestion of
nutrients and absorption of
oxygen
*Chronic respiratory infections
*Life expectancy of 30
Ribosomes : Treacher-Collins
Results from mutations in genes that code for proteins essential for the formation of ribosomes.
The mutations lead to a reduced production of rRNA which may lead to apoptosis of certain cells (dealing with facial development).
Mitochondria : MELAS Syndrome
This is a rare disorder from mutations in mitochondrial DNA. Mitochondrial disorders impact a lot of different areas of the body as mitochondria is involved in ATP generation in all cells.
- MELAS is named for the different presentations like Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like episodes.
- Very noticeable in muscles and nervous system.
- Accumulation of lactic acid in the blood, spinal fluid, brain.
- Symptoms include seizures, headaches, recurrent vomiting, muscle weakness, dementia.
