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Transcript of Cell Biology
- Earliest microscope = light microscope
- Light passes through specimen
and then through a lens, magnifying
it to the eye
Newer, more advanced microscopes allow for an even closer look
Electron microscopes use electron beams which pass through a specimen or onto its surface
Since resolution is inversely related to radiation wavelength, electron microscopes have better magnification as electron beams have shorter wavelengths than light
Scanning electron microscope (SEM) scans the surface of a sample coded with gold to create a 3D image of the surface
Transmission electron microscope (TEM) shows the internal structure of cells by sending an electron beam through a thin section of the specimen stained with heavy metal atoms to increase density in some areas
The problem with electron microscopes is they cannot study living cells
Although advanced, microscopes do have limitations
Magnification's the ratio of an object's image to its real size
Resolution measures an image's clarity, or the smallest distance separating two points in which the points can be distinguished
Contrast shows differences in sample pieces like staining or labeling helping things to visually stand out
Chromosomes carry genetic information and contain a long DNA strand with its proteins
The DNA and proteins making up chromosomes are called chromatin, which are indistinguishable blob until chromosomes condense to become distinguishable
Each species has a unique number of chromosomes
The nucleus contains most of eukaryote's genes and has an average diameter of 5 micrometers
The nuclear envelope is a double membrane made up of lipid bilayers that encloses the nucleus
The envelope contains pores which connect the inner and outer membrane of the nucleus and includes proteins that regulate macromolecules like RNA
The nuclear side of the envelope is lined by the nuclear lamina of protein filaments that support the nucleus while inside the nuclear matrix of protein fibers does the same
The Eukaryotic Cell's Gene
Nucleus: House most of the cell's DNA, in form of chromsomes.
Overview: The Endomembrane System
The endomembrane system is the membranes in and around the cell connected through contact or vesicles that carry out a variety functions:
of Cell Theory
In 1665, English scientist Robert Hooke discovered (dead and empty walls of) plant cells while studying a cork slice with a compound microscope
Hooke's Dutch contemporary, Anton van Leeuwenhoek, discovered tiny unicellular organisms which he called animalcules
carter's gray-ish area
Cells: The Units of Life
Biologists originally thought that a eukaryotic cell's organalles floated freely in the cytosol.
Found cytoskeleton :
a network of fibers extending throughout the cytoplasm
Organizes the cell structures and activities
Section 4: The Endomembrane System & Cell Theory
Roles of Cytoskeleton
Mechanical support to the cell & maintain its shape
Especially for animal cells!
Its strength and resilience from the architecture
In 1838, German botanist Matthias Schleiden deduced all plants were made of cells
In 1839, German biologist Theodor Schwann states that all animals are also made of cells
In 1855, German physician Rudolf Virchow deduced new cells are produced by division of other cells
Matthias Schleiden: top left
Theodor Schwann: bottom left
Rudolf Virchow: right
All living things are composed of cells
Cells are the most basic unit of life
New cells are produced only from existing cells
synthesizing and transporting proteins
metabolizing and moving lipids
The system is made of the:
The ER is a membrane network connected to the nuclear envelope
Inside the space between membranes is an internal cavity called the ER lumen
The ER is made of two distinct components:
The Smooth ER: which lacks ribosomes on its surface
The Rough ER: with ribosomes all over its surface
The Smooth ER
The Smooth ER plays an important role in the metabolism of carbohydrates and in the synthesis of fats, particularly animal steroid and sex hormones
The Smooth ER also helps detoxify drugs and poisons by adding hydroxl groups to their molecules to make them more soluble to flush, with drug use increasing the presence of Smooth ER and thus increasing drug tolerance
Smooth ER also stores calcium ions to be released as triggers for activities like muscle cell contraction
The Rough ER
The Rough ER produces proteins for secretion
Polypeptide chains from bound ribosomes are drawn into ER lumen to fold into the native shape
Most of these proteins bond with carbohydrates to make glycoproteins
The proteins are then wrapped in membrane transport vesicles to be taken to other areas
The ER also produces membrane proteins and phospholipids for itself and other membranes
The Golgi Apparatus
The Golgi apparatus is an organelle made of flattened membrane sacs called cisternae which store, modify, and ship out products of the ER
Vesicles near the Golgi transfer material through and out of the Golgi
The Golgi has two sides:
A cis face near the ER that absorbs vesicles and their contents into its membrane
A trans face which releases vesicles and the modified materials
The Golgi also creates noncellulose polysaccharides
The Golgi refines its products in stages with different cisternae performing different functions, the cisternae move from cis to trans
The Golgi tags products for different areas using phosphate groups
Lysosomes are membranous sacs of enzymes that hydrolize (break down) macromolecules in animal cells
Due to the acidic environment inside lysosomes, a cell can self-digest if many leak
Lysosomes have two major digestion types:
In autophagy, a damaged organelle or part of the cytosol is surrounded by a double membrane which a lysosome fuses with so the enzymes can dissolve what is inside for reuse by the cell, allowing the cell to recycle materials
In phagocytosis, cells like amoebas engulf food to form a food vacuole which fuses with a lysosome for food digestion to create monomer nutrients for the cell
If people inherit lysosomal storage diseases, their lysosomes lack certain functioning hydrolytic enzymes and engorged lysosomes containing the indigestible material begin to interfere with cellular activities
In Tay-Sachs disease, found mostly in Ashkenazi Jews, a lipid digesting enzyme is not functioning and the brain is impaired by lipid accumulation that slowly kills neurons, causing mental disorders, loss of coordination, and death
Vacuoles are large vesicles made from the ER and the Golgi apparatus which selectively transport materials.
There are several types of vacuoles
Food vacuoles carry food caught in phagocytosis
Contractile vacuoles are found in freshwater protists and pump excess water out of the cell to control the concentration of molecules in the cell
Most fully grown plant cells contain a central vacuole containing cell sap and serves as the plant cell's main storage area for inorganic ions
The vacuole is a key factor in plant cell growth as the cell grows when the vacuole absorbs water, allowing the cell to become larger without creating much new cytoplasm, so the ratio of volume to surface area is near even
In plants and fungi, certain vacuoles perform enzymatic hydrolysis like lysosomes
In plants, smaller vacuoles hold reserves of important organic molecules, pigments, and poisonous or unpalatable compounds affecting animals to ward them off
Reece, Jane B., Lisa A. Urry, et al. Campbell Biology. AP 9th Edition. San Francisco: Pearson Education, Inc., 2011. 94-122. Print.
Green, Edwina R,. "The discovery of “animalcules”." Encyclopedia Britannica. Encyclopædia Britannica, Inc., 13 Oct 2013. Web. 15 Nov 2014. <http://www.britannica.com/EBchecked/topic/66054/biology/48848/The-discovery-of-animalcules>.
"Tay-Sachs disease." Genetics Home Reference. U.S. National Library of Medicine, n.d. Web. 15 Nov 2014. < http://ghr.nlm.nih.gov/condition/tay-sachs-disease>.
A dome tent
stabilized by a balance between oposing forces exerted by its elements
provides anchorage for many organelles and cytosolic enzyme molecules
can be quickly dismantled in one part of the cell and reassembled in a new location
change the shape of the cell
cell motility = change in cell location + limited movements of parts of the cell
interaction of the cytoskeleton with motor proteins
ex) Work with plasma membrane molecules so the whole cell can move along fibers outside the cell
ex) Inside the cell, organelles use motor protein "feet" to "walk" to their destinations along a track provided by the cytoskeleton
Roles of Cytoplasm CNTD'
Manipulation of plasma membrane, making it bend inward to form food vacuoles or other phagocytic vesicles
ex) material circulation within large plant cells
Components of the Cytoskeleton
2 interwined strands of actin, each a polymer of actin subunits
Wall consists of 13 columns of tubulin molecules
Grows in length by adding tubulin dimers
can be disassembled
"plus end" - one end can accumulate/release tubulin dimers much faster
25 nm with 15-nm lumen
tubulin, a dimer consisting of alpha-tubulin and beta-tubulin
Maintenance of cell shape
Chromosome movement in cell division
Centrosomes & Centrioles
Microtubules grow out from here
these microtubules function as compression-resisting girders of the cytoskeleton
9 sets of triplet microtubules arranged in a ring
Before replicate before an animal cell divides
Cilia and Flagella
Means of motility
Unicellular eukaryotes - cilia / flagella as locomotor appendages
sperm - flagella
Extend from cells and move fluid over the surface of the tissue
Occur in large number but short
beating pattern - "oars"
Nonmotile cilia - signal-receiving "antenna" for the cell
Limited to 1 or a few per cell but longer
undulating motion ("tail of fish")
Has a group of microtubules sheathed in an extension of the plasma membrane
9 doublets of microtubules in ring w/ 2 single microtubules in center
The microtubule assembly is anchored in the cell by a basal body
Flexible cross-linking proteins connect the outer doublets to each other and to 2 central microtubules
Performs a complex cycle of movements
bending movements of organelles
Forces exerted by dynein "walking" cause the doublets to curve, bending the cilium/flagellum
Maintenance of cell shape
Changes in cell shape
3D network of microfilaments inside the plasma membrane helps support the cell's shape
Cortex become more gel-like than the interior cytoplasm
In animal cells like intestinal cells, bundles of microfilaments make up the core of microvilli
Fibrous proteins supercoiled into thicker cables
more permanent fixtures of cells
even persists ever the cell dies
1 of several different proteins depending on cell type
Maintenance of cell shape
Anchorage of nucleus and other organelles
Formation of nuclear lamina
Section 6: The Cytoskeleton is a network of fibers that organizes structures and activities in the cell
Section 7: Extracellular components and connections between cells have coordinate activities
Plant Cell Walls
Thicker than plasma membrane
Chemical composition varies
Basic design is consistent
Microfibrils made of polysaccharide cellulose are synthesized by cellulose synthase and secreted to the extracellular space
Strong fibers in a "ground substance" (matrix)
Protects plant cells
Maintains its shape
Prevents excessive uptake of water
Hold the plant up against the force of gravity
Primary cell wall
relatively thin and flexible
Cellulose fibrils affect the growth pattern of cells
microtubules in the cell cortext guide cellulose synthase as it synthesizes and deposits the fibrils
Between primary walls of adjacent cells
a thin layer rich in pectins
Glues adjacent cells together
When the cell matures and stops growing,
strengthens its wall
Some do this by secreting hardening substances into primary wall
Secondary Cell Wall
Between the plasma membrane and primary wall
Deposited in several laminated layers
Has a strong and durable matrix
cell protection and support
Plant cell walls commonly perforated by plasmodesmata
Extracellular Matrix (ECM)
Main ingredients : glycoproteins
Most abundant : collagen
Forms strong fibers outside the cell
Accounts for 40% of the total protein in human body
Collagen fibers embedded in a network woven from proteoglycans
Consists of a small core protein with many carbohydrate chains covalently attached
Large proteoglycan complex
hundreds of proteoglycans noncovalently attached to a single long polysaccharide molecule
Attach some cells to the ECM
Fibronectin & other ECM proteins bind to integrins
Cell surface receptor proteins built into the plasma membrane
Span the membrane and bind on their cytoplasmic side to associated proteins attached to microfilaments of the cytoskeleton
Transmit signals b/w ECM and cytoskeleton
integrate changes occurring inside / outside of the cell
Roles of ECM
Regulate cell behavior
Influence the activity of genes in the nucleus
Help coordinate the behavior of all the cells of tissue
Hazel Choi, Jo Sinta, Carter Quan, Robert Aliberti
Used to disassemble cells and makes it possible to isolate their organelles
A centrifuge is used to "scramble" the cells.
The faster the centrifuge, the smaller
By studying the individual components of cells, scientists are able to study the functions of them
Prokaryotic and Eukaryotic Cells
All cells have cytosol and all their components are suspended in that
All cells have chromosomes and carry DNA
All cells have ribosomes, which make proteins from instructions from genes.
All have an outer plasma membrane that acts as a selective barrier.
Major Difference Between Prokaryotes and Eukaryotes:
Location of the DNA
Eukaryotes have the DNA in the nucleus
Prokaryotes have their DNA in a nucleoid
The nucleoid, unlike a nucleus, is not enclosed in a membrane.
Eukaryotic cells have cytoplasm, in which cytosol suspends the organelles and lies between the nucleus and the plasma membrane
Eukaryotes are much larger than prokaryotes
Bacteria, prokaryotes, tend to be from 1-5 um in diameter, while eukaryotes are 10-100 um
When a cell grows the volume grows more than surface area
A larger surface area is important to cells that are required to exchange lots of materials.
Some have microvilli, little projections, to increase surface area
Direct connection between cells that coordinate the behavior of all the cells of tissue
Plasmodesmata in Plant Cells
membrane-lined channels filled with cytoplasm
Plamsa membranes of adjacent cells line the channel of each plasmodesma and thus are continuous
Wter and small solutes pass through
Certain proteins and RNA molecules too
plasma membranes of neighboring cells are very tightly pressed against each other
Prevent leakage of extra-cellular fluid across a layer of epithelial cells
fastens cells together into strong sheets
Attach muscle cells to each other in a muscle
provide cytoplasmic channels from one cell to an adjacent cell
similar to plasmodesmata in plants
Consist of membrane proteins that surround a pore where small molecules can pass through
Necessary for communication b/w cells
Ribosomes: Carry out DNA information by involving in synthesis protein
A prominent structure within the nondividing nucleus.
where rRNA synthesized from instruction of DNA
Protein imported from the cytoplasm are assembled with rRNA into subunits of
Made of ribosomal RNA and protein
Cellular components that carry out protein synthesis.
Ribosomes can build protein in either
cytosol and ribosomes suspend in cytosol called:
free ribosomes. Free ribosomes produce protein that function within the cytosol.
Out side of the endoplasmic reticulum, ribosomes attached to ER called:
Bound ribosomes. Bound ribosomes make proteins that insert into membranes.
Evolutionary origins of Mitochondria and Chloroplasts: endosymbiont theory
Once upon a time, an early ancestor of eukaryotic cells met an oxygen-using non-photosynthetic prokaryotic cell. They fall in love and got a relationship name: endosymbiont. They adopted a photosynthetic prokaryote and became the ancestor of eukaryotic cells that contain chloroplasts and reproduced bunch of off-spring and happily lived ever after.
Mitochondria: Chemical Energy conversion and site of cellular respiration
Mitochondria are found in almost all eukaryotic cells.
Number of mitochondria in a cell various from one to thousands, due to different levels of cells' metabolic activities.
Mitochondria have two membranes that consists of phospholipids bilayer with unique collection of embedded proteins.
Outer membrane is smooth and inner membrane is convoluted. Infoldings on the inner membrane called cristae.
Inner membrane divides mitochondria into two internal compartments: intermembrane space and mitochodrial matrix, which enclosed by the inner membrane.
Cristae give the inner mitochondrial matrix a large surfae area, therefore enhancing the cellular respiration.
mitochodrial matrix contains enzymes, mitochodrial DNA and free ribosomes.
Chloroplasts: Capture of Light Energy
Choloroplasts contain the green pigment chlorophyll, enzymes, and other molecules that function in the photosynthetic production of sugar.
Chloroplasts enclosed by two membrane, and inside chloroplasts is pancake-like container called thylakoid.
Stack of thylakoids called granum.
The fluid outside thylakoids called stroma, it contains DNA, Enzymes and some ribosomes.
Chloroplasts is a specialized member of a family of closely related plant organelles called plastids.
Peroxisome: What is this?
Peroxisome are specialized metabolic compartments bounded by a single membrane.
It contains enzymes that transfer hydrogen atoms from substrates to oxygen, producing hydrogen peroxide as a by-product; peroxide is converted to water by another enzyme.
How peroxisome related to other organelles is still an open question.
Plant Cells vs. Animal Cells
All other organelles
Centrosomes (with centrioles)
Flagella (but some plant sperm have them)