The Cell (midterm topic 2)
What is a transport vesicle from the Rough ER and what is its function?
pinched off from the Rough ER and holds proteins -transported to the golgi apparatus, and contents of ER lumen are mixed with golgi apparatus
What does the endomembrane system regulate?
regulates protein traffic and performs metabolic functions in the cell
What are vesicles?
sacs made of membrane
What is cisternae?
the folded series of tubules that make up the ER
What are the purple dots in these blue transport vesicles from the Rough ER?
vesicle filled with proteins that have budded off from ER and fuse to golgi apparatus' cis face.
What are the functions of the golgi apparatus?
-An organelle responsible for the functional maturation of proteins and some polysaccharides. -Similar in structure to the smooth ER, and is usually seen as a series of stacked discs or sacs (cisternae) within the cell. -Material in transport vesicles from the RER fuse with the Golgi apparatus at its cis face. Processed material leaves at the trans face. -There is a definite direction or polarity to the structure. -Material is transferred from one disc to another by transport vesicles that are guided by special signaling proteins or tags attached to the outside of the vesicles.
Explain the modification process of proteins through the golgi apparatus
-As proteins travel through the Golgi apparatus they are modified until they become the final product that can either be used by the cell or released from it by secretion. -This modification process often occurs using specialized enzymes that are located at different points between the cis and the trans part of the Golgi.
What is Cell fractionation? Explain
-Cell fractionation takes cells apart and separates the major organelles from one another -Cells are ground up in a blender and the homogenate is then subjected to centrifugation. Larger particles will "pellet" to the bottom, smaller pieces remain suspended in the "supernatant" Homogenate= resulting mixture Supernatant= liquid above the pellets
Name the organelles that are found in plant cells, but not animal cells
-Central Vacuole -Chloroplast -Plasmodesmata -Cell Wall
What is the Nucleolus?
-Consists of ribosomes and RNA. -The nucleolus is the site of synthesis of ribosomes (and then they are carried out through nuclear pore complexes to cytoplasm)
What are the functions of lysosomes?
-Contain enzymes important for the digestion of all the major types of macromolecules. -Lysosomal enzymes work best in the acidic environment (pH 5) inside the lysosome. (protection for cell if it were to burst- enzymes wont function and eat cell) -Some types of cells can ingest food in vacuoles in a process called phagocytosis ( ex. macromolecules into monomers) - lysosomes break the contents down -Lysosomes also use enzymes to recycle the cell's own organelles and macromolecules, a process called autophagy
What are Eukaryotic cells characterized by having?
-Eukaryotic cells have internal membranes that compartmentalize different functions. -DNA in a nucleus that is bounded by a membranous nuclear envelope. -Membrane-bound organelles. -Cytoplasm in the region between the plasma membrane and nucleus (note: cytosol is the fluid portion of the cytoplasm).
Name the organelles in eukaryotic cells that are not found in plant cells
-Flagellum -Centrosome -Lysosome
What is the structure of mitochondria?
-Found in virtually all eukaryotic cells. -Vary in size from 1 -10µm (about the same size as a bacterium...supporting the endosymbiont theory). -Made up of a an outer smooth membrane, and an inner membrane that is folded into a series of convolutions called cristae. -The rest of a mitochondrion is made up of the matrix that contains many of the enzymes important for cellular respiration where the energy derived from carbohydrates and lipids is transferred to the molecules, particularly ATP, that are used as energy sources for many cellular processes.
How did the internal membranes of eukaryotic cells form?
-Imagine a prehistoric prokaryotic cell with DNA and ribosomes attached to the plasma membrane. -Invaginations of surface membrane of ancient prokaryotic cell led to internalization of membranes creating rough and smooth ER. And eventually the membrane from the outside pinched off. -DNA became bound with a double membrane.
Why are cell organelles important and what do they allow eukaryotic cells to do?
-Important for compartmentalization within the cell - the physical separation of cell functions. Allows different chemical environments to exist within the cell. Two examples: 1. pH; allows enzymes to function in an isolated environment. Some hydrolytic enzymes require a low pH to function. These enzymes are sequestered in organelles. If they "escape" to the cytosol, they are largely ineffective. 2. Ionic gradients; generation of ATP in mitochondria requires an ionic gradient that is established across the mitochondrial inner membrane.
What is the purpose of the microvilli in a eukaryotic cell?
-Increase surface area of the cell -Helps to increase rate of uptake of molecules from extracellular space (small intestine) -internal structure of microfilaments inside to give stability
What is the purpose of the centrosome in a eukaryotic cell?
-Involved in cell division (mitosis & meiosis). -Location of the initiation of the growth of microtubules
What is the purpose of the flagella in a eukaryotic cell?
-Involved in cell motility (not on all cells...only on sperm in mammals). -Composed of a cluster of microtubules in an extension of the plasma membrane
How have eukaryotes exploited the fact that more cells increases the surface area while keeping the total volume constant, creating a perfect SA-V Ratio?
-Larger organisms do not have larger cells, they just have more cells. -The internalization of membrane bound structures has effectively increased the surface area of these large cells (imagine each small box as being an internal, membrane-bound organelle)
What is the purpose of the ribosomes in a eukaryotic cell?
-Location of protein synthesis -Either free in cytosol or bound to rough ER or nuclear envelope
Within plant cells, what is the purpose of the cell wall?
-Maintain's cell shape -made from cellulose (unbranched and hydrogen bonded)
What is the purpose of the cytoskeleton of a eukaryotic cell? What are the three types?
-Maintains cell shape, and provides support and anchor points for organelles. -Provides the mechanisms for cell (flagellae and pseudopodia) and organism movement (e.g. muscle contraction). -Provides tracks for motor proteins that move materials and organelles within cells. There are three major types of cytoskeletal components: Microfilaments Intermediate filaments Microtubules
What are nuclear pores?
-Many openings called nuclear pores extend through the nuclear envelope. Nuclear pores control the movement of substances between the nucleus and the cytoplasm. -Inside each pore is a pore complex consists of eight very large protein granules arranged in an octagon
What is the purpose of the golgi apparatus in a eukaryotic cell?
-Membrane bound organelle -Modifies and sorts proteins delivered to it from the ER -Full of enzymes that modify and mature proteins, by adding groups to them to give final functionality
What are prokaryotic cells characterized by?
-No nucleus (the nucleoid is the region where the DNA is located but is not membrane bound) -no membrane-bound organelles.
Explain the function of ribosomes
-Ribosomes are the sites of protein synthesis. -They consist of a type of RNA, ribosomal RNA, and more than 50 proteins.
What are eukaryotic cells? What domains encompass all of the eukaryotic cells?
-The genetic material is physically separated from the rest of the cell by a membrane. -Protists, fungi, animals, and plants all consist of eukaryotic cells
What is the nuclear envelope?
-The nucleus is surrounded by the nuclear membrane. -It consists of a double, folded bilayer bounded on the inside by the nuclear lamina, a network of protein fibers that helps maintain its shape -Anything that passes between the nucleus and cytoplasm needs to pass through this membrane. Passage points are called nuclear pores in the membrane that traverse the double membrane.
What is the structure of chloroplast?
-The organelle that is responsible for photosynthesis: transforming sunlight into forms of energy that plant cells can use. -Structure is similar to a mitochondrion in that chloroplasts have a double membrane and a matrix, in this case called the stroma. -Chloroplasts have a series of discs - thylakoids, which in some cases are stacked into structures called grana. The thylakoids are where chlorophyll is located and is the site of photosynthesis.
What are prokaryotic cells? What domains encompass all of prokaryotic cells?
-These cells lack nucleus and internal membrane-bound structures. -Only organisms of the domains Bacteria and Archaea consist of prokaryotic cells -between 1 and 10 micrometers
Explain the purpose of the plasma membrane of eukaryotic cells
-a continuous structure that separates the inside and outside of the cell. -made of phospholipid bilayer -Amphipathic Proteins are inserted in to the membrane - ex transport proteins (provides aqueous pathway through membrane) -Carbohydrates attached to the proteins of the outside of the membrane (called glycoproteins) acting as cell surface markers (ex Blood Type) -Carbohydrates attached to lipids on the outside of the membrane (called glycolipids) and also used for cell surface markers The plasma membrane acts as a selectively permeable barrier. Some substances can diffuse in and out; others cannot. -The plasma membrane is an interface for cells where information is received from the extracellular environment. -The membranes allow the cell to maintain a relatively constant internal environment as well as separate and distinct chemical and structural environments
What is the function of the lysosome in a eukaryotic cell?
-membrane bound organelle important for digestion -Enzyme-filled vesicle that digests ingested molecules -acidic environment
In order of smallest to biggest, what are the three types of cytoskeleton of the eukaryotic cell?
-microfilaments -Intermediate filaments -Microtubules
What are the main functions of microfilaments (Actin filaments)?
-muscle contractions -move amoebas -swirls cytoplasm
Explain the purpose of the smooth Endoplasmic Reticulum
-network of membranous sacs -devoid of ribosomes, important for synthetic, metabolic and storage functions -Synthesize lipids -Metabolize carbohydrates -Detoxify drugs and poisons -Store calcium ions
What are the two sides of the golgi apparatus? What are they called?
-receiving side is the cis face -shipping side is the trans face
Within plant cells, what is the purpose of the central vacuole?
-storage for toxins -hydrolysis of macromolecules -basically a membrane bound bag of water
Where are ribosomes found?
1) Free in the cytoplasm 2) Bound to the endoplasmic reticulum (RER) 3)Mitochondria and Chloroplasts
What does the endomembrane system consist of?
1) Nuclear envelope 2) Endoplasmic reticulum (smooth and rough) 3) Golgi apparatus 4) Lysosomes 5) Vacuoles 6) Plasma membrane These components are either continuous or connected via transfer by vesicles.
What are 3 optical methods used to enhance the CONTRAST for cells visualized with a light microscope?
1) Phase contrast microscopy - increases the contrast between the background and the cell (keeps cell alive) 2) Differential interference contrast (DIC or Nomarski) - changes optical view 3) Confocal with fluorescence - specimen is stained with a dye that fluoresces and the tissue can be optically sectioned to be seen in 3D (good for thick cells)
Explain the process a protein in a secretory vesicle takes to get secreted
1) Ribosome synthesizes the protein on the membrane of the ER 2) protein enters ER and is matured and eventually packaged in a vesicle and taken to the golgi apparatus' cis side 3) The protein travels through the golgi apparatus and buds off of the golgi apparatus's trans side in a secretory vesicle that fuses with the cell membrane - This is how insulin is secreted
What are the two types of Electron Microscopes (EMs) used to study subcellular structures? Explain each of their functions
1) Scanning Electron Microscope (SEMs) - focus a beam of electrons onto the surface of a specimen, providing images that look 3-D. 2) Transmission Electron Microscope (TEMS) - focus a beam of electrons through a specimen - TEMs are used mainly to study the internal structure of cells
Once proteins are made on the rough ER, where do they go in the cell?
1) They are released outside the cell (secreted) 2) They are transported and inserted into the plasma membrane 4) They become part of an organelle -To make this happen, all proteins need to be directed to the appropriate place in the cell.
What are the two layers of nuclear membranes of eukaryotic cells that make up the nuclear envelope?
1) inner nuclear membrane 2) outer nuclear membrane -have nuclear pore complex as well (pores for transportation- this is how mRNA gets out of nucleus to cytoplasm for translation)
What are the 4 basic features of all cells?
1)Plasma membrane 2)Semifluid substance called cytosol 3)Chromosomes (carry genes) 4)Ribosomes (make proteins)
What happens to the proteins that bud off from the trans side of the golgi apparatus?
1)Turn in to lysosomes or 2)fuse in to plasma membrane and contents are secreted
What are the two main products of the Golgi that bud off from the trans side of the Golgi
1. Lysosomes—enzymatically filled organelles important for digestion. 2. Secretory vesicles—membrane bound organelles that release their contents to the outside of the cell.
How does a cell target proteins and bring them to the ER?
1: Ribosomes are free in cytoplasm where protein synthesis begins (in the cytosol- during translation) 2, 3:If first part (in green) of protein is a signal peptide recognized by a signal recognition particle (SRP), complex is directed to ER membrane where SRP receptor protein binds SRP. 4, 5: Protein synthesis continues on the ER membrane. 6: Final protein product ends up inside ER lumen...and ribosome is released to be re-used. Proteins can also me put in to the membrane of the ER Net result is that protein can then be targeted to another part of the cell or for secretion.
What is the smallest single cell that humans can see with the naked eye?
At 1mm, we can see frog eggs
What are centrosomes in animal cells?
Centrosomes are important for cell division (mitosis) in animal cells. They are made from microtubules and other proteins (blue). Two centrioles are oriented at right angles to each other.
Explain the similarities and differences between cilia and flagella
Cilia and flagella are covered by the cell's plasma membrane. Flagella are usually longer than cilia, and cells that have them usually only have one or two. Cilia are usually present in great numbers.
Within plant cells, what is the purpose of the plasmodesmata?
Cytoplasmic channels between adjoining cells to pass material and communicate
What kind of microscope is used to visualize sub-cellular structures?
Electron Microscopy (EM) -Scanning Electron Microscope (SEMs) -Transmission Electron Microscope (TEMS)
True/False: There are ribosomes within the lumen of the ER
False. Only on the outside
True/False: The ribosomes on the Rough ER are permanent
False. after they synthesize protein, they are released to be reused
What is the structure of microtubules?
Hollow tubes
What is Chromatin?
How chromosomes are in the nucleus when the cell is not dividing! -Consists of DNA and its associated proteins, in particular a group of proteins called histones around which the DNA is wound. -In addition, there are many regulatory proteins that function in controlling gene expression -uncoiled chromosomes that are wrapped with histones -when cell wants to divide it coils up its chromatin and makes it a chromosome, then cell divides. -chromosomes are condensed chromatin.
What kind of microscope is used to visualize most cells? How does it work?
Light Microscopy (LM) -visible light is passed through a specimen and then through glass lenses. -Lenses refract (bend) the light, so that the image is magnified. -Staining with a dye is used to enhance visibility of cells
Where are the Intermediate filaments found?
Make up the nuclear lamina (helps maintain nucleus shape)
Within plant cells, what is the purpose of the chloroplast?
Membrane bound organelles that are important for photosynthesis
How are microtubules important for cell motility?
Microtubules are structural components of cilia and flagella.
How big are cells?
Most cells are between 1 and 100 μm in diameter (yellow portion of figure).
In the technique of differential centrifugation, what is in the pellet when you spin the supernatant at 80,000x the force of gravity for 60 min?
Pellet rich in "microsomes" which are pieces of membrane
In the technique of differential centrifugation, what is in the pellet when you spin the supernatant at 20,000x the force of gravity for 20 min?
Pellet rich in mitochondria and chloroplasts
In the technique of differential centrifugation, what is in the pellet when you spin the supernatant at 150,000x the force of gravity for 3 hours?
Pellet rich in ribosomes
What happens to the polypeptides (proteins) once they are synthesized on the ribosomes of the rough ER during translation?
Polypeptides can be directed one of two ways: 1. to the ER's cisternal space 2. incorporated into the ER membrane itself -Polypeptides that move into ER's cisternal space can be further modified to change their folding, and/or have carbohydrate groups added to begin the process of protein maturation. -Some polypeptides entering the ER have address information that instructs their final destination (secretion is the default destination- when there is no address). -Some membrane and lumen proteins remain in the ER to maintain its function -others are transported to the Golgi apparatus where they are modified further
What are the functions of the microtubules of the cytoskeleton?
Provides tracks for motor proteins that move materials and organelles within cells.
Explain the function of the rough Endoplasmic Reticulum
The ER is a network of interconnecting membrane enclosed sacs distributed throughout the cytoplasm. -has membrane bound ribosomes important for synthesis of proteins destined for other compartments or for secretion
What is the fundamental unit of life?
The cell. The simplest unit of life is the cell, and all organisms are composed of cells.
What is the endosymbiont hypothesis?
The endosymbiont theory of the origins of mitochondria and chloroplasts in eukaryotic cells An archaeabacteria (eukaryote) host cell engulfed (endocytosed) a non-photosynthetic, 02-using prokaryote bacterium, which over many generations became the mitochondria within a heterotrophic (nonphotosynthetic) eukaryote. The Heterotrophic nonphotosynthetic eukaryotic host, then engulfed a photosynthetic prokaryote (cyanobacteria) and became a photosynthetic eukaryote
What proteins do the ribosomes that are in the cytoplasm make?
These synthesize cytoplasmic soluble proteins (aq)
What proteins do ribosomes make that are bound to the endoplasmic reticulum
These synthesize proteins that are more insoluble and are destined for membranes and secretion
How does the golgi apparatus get proteins to modify?
Transferred by transport vesicles from the rough ER to the cis side of the golgi apparatus.
True/False: About half of the cell's membrane is ER membrane.
True
True/False: Approximately 15% of the entire fluid volume of the cell is inside the ER
True
True/False: Large cells have a smaller surface-to-volume ratio than do smaller cells
True
True/False: Only about 5% of the membrane of a eukaryotic cell is the plasma membrane
True
True/False: In eukaryotic cells, the nuclear envelope and the ER have one continuous membrane
True! Because of the theory of invagination and pinching off of membrane
What are the functions of mitochondria and chloroplast?
Used for energy metabolism -Both of these organelles can move around the cell and divide. -They have their own ribosomes and DNA that are used to synthesize some of their proteins. -These features suggest that at one time they were independent prokaryotic organisms that developed a symbiotic relationship with other cells.
In the centrosome, what is the purpose of the centriole?
We are unsure what the purpose is (it can be taken out and the cell will still divide)
When does translation (proteins being made from mRNA in the ribosomes) in the cytoplasm stop?
When the first part of a protein is a signal peptide, then once SRP (Signal recognition particle) grabs on to the ribosome, translation stops until it is attached to the wall of the Rough ER
What is the nuclear lamina?
a network of protein fibers in the nuclear membrane that helps maintain its shape. -Made of intermediate filaments and proteins -space between inner membrane and chromatin
What are microfilaments made of?
a protein called actin -called filamentous actin when 2 strands intertwine
What is a plasma membrane?
a selective barrier at the surface of cells that regulates the passage of oxygen, nutrients, and wastes to service the volume of every cell
What are microtubules made of?
alpha and beta tubulin dimers, called protofilaments, and 13 of them make up a microtubule
What is the internal compartment of the ER called?
cisternal space -the lumen (inner space) is a separate part of the cell. -It has a distinct protein and ion composition
What is cytosol?
cytosol is the fluid component of the cytoplasm
In animal cells, where do microtubules grow from?
from a centrosome near the nucleus
How is differential centrifugation used for cell fractionation? Explain the process
it is used to isolate cell components based on their size and density 1) Tissue cells put in blender to grind up cells 2) Then put homogenate (mixture) in centrifuge 3) supernatant (liquid above pellet) can keep being spun down, pellet can be studied
What are intermediate filaments made of?
keratins coiled together
What are the functions of intermediate filaments?
maintenance of cell shape, anchorage of nucleus and certain other organelles, formation of nuclear lamina
What are the main functions of microtubules?
maintenance of cell shape, cell motility, chromosome movements in cell division, organelle movements
Does all of the ribosomal material, specifically mRNA made in the nucleolus leave and go to the cytoplasm?
no, there is an exception, the mRNA that codes for ribosomes, never leaves the nucleus (specifically, nucleolus) because ribosomes are made in the nucleolus.
Do ribosomes that stay in the cytoplasm have a signal peptide?
no, they do not have signaling that they need to be moved to the ER
What is the nucleus surrounded by?
nuclear envelope
Where is most of the DNA in a eukaryotic cell?
nucleus
In the technique of differential centrifugation, what is in the pellet when you spin the homogenate at 1000x force of gravity for 10 min?
pellet rich in nuclei and cellular debris (parts of cells)
