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Cell Strucuture and Membrane

Terms in this set (58)

What is the cytosol and its function?
The region that is outside the organelles but inside the plasma membrane. It is the cenral coordinating region for many metabolic activities of eukaryotic cells. These activities are catalyzed by enzymes: a protein that accelerates the rate of a chemical reaction. These pathways are anabolic and catabolic. Catabolism is the breakdown of of a molecule into smaller components to be used for macromolecules. Anabolism is the synthesis of cellular molecules and macromolecules. Protein synthesis (translation) occurs here, on free ribosomes.
What is the nucleus and its function?
An organelle that contains most of the genetic.The primary function of the nucleus involves the protecion, organization, replication and expression of the genetic material. Also is responsible for the assembly of ribosome units. This occurs in the nucleolus, a prominent region in the nucleus of nondividing cells. The ribosomal protein is imported into the nucleus to the nucleolus for the assembly of the ribosome. It is encolosed by a nuclear envelope which has nuclear pores which allow the passageway of molecules and macromolecules. Chromosomes, which are composed of DNA and protein. The complex formed by DNA and such proteins are called chromatin. The nuclear matrix consists of two parts: the nuclear lamina which is composed of intermediate filaments that line the inner nuclear membrane and an internal nuclear matrix which is connected to the lamina and fills the interior of the nucleus. The nuclear matrix serves to organize the chromosomes within the nucleus. Each chromosome is located in a distinct nonoverlapping chromosome territory.
What is the endomembrane system?
Plasma membrane, nuclear envelope, smooth and rough endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles and peroxisomes.
What are ribosomes composed of?
A small and a large subunit. Each subunit contains one or more RNA molecules and several types of proteins.
What is the rough endoplasmic reticulum and its function?
A network of membranes that form flattened, fluid filled tubules. The lumen is the area enclosed the ER membrane. The rough ER is studded with ribosomes.Plays a key role in the sorting of proteins destined for other organelles and the insertion of proteins into the ER membrane. Glycosylation also occurs.
What is the smooth endoplasmic reticulum and its function?
Continuous with rough ER but has no ribosomes attached to it, also increases surface area for enzymes. Detoxification, carbohydrate metabolism and muscle contraction (due to high levels of calcium) also occur. Also is important for the synthesis and modification of lipids and phospholipids.
What is the Golgi apparatus and its function?
Three areas, the cis(near the ER), medial and the trans(near the membrane). Is responsible for processing, protein sorting and secretion. Glycosylation continues in the Golgi. Proteolysis also occurs in the Golgi, proteases cut proteins into smaller functional peptides. For example, proinsulin undergoes proteolysis into insulin. Also packages things into secretory vesicles which fuse with membrane in to the extracellular environment.
What is the secretory pathway?
Proteins are synthesized into the ER membrane, travel to the Golgi and are the packaged into secretory vesicles destined for the outside of the cell.
What is exocytosis and endocytosis?
Exocytosis is the process by which vesicles fuse with membrane relaeasing their contents. Endocytosis is where vesicles fuse with the membrane releasing their contents into the cell.
What are lysosomes and their function?
An organelle that is found in animal cells that are able to cut macromolecules. They contain acid hydrolases which are hydrolytic enzymes that use a molecule of water to break a covalent bond. They breakdown molecules that come into the cell via endocytosis and also recycle used macro(molecules)
What are vacuoles and their function?
Vacuoles are fluid filled compartments. They are varied in their funtions and it depends on the type of cell. In animals, vacuoles are used to temporarily store materials or transport substances and are called storage vesicles. Plant cells have a large central vacuole, enclosed by a membrane known as a tonoplast. It has a huge amount of water, enzymes and inorganic ions and sometimes proteins and pigments. It performs a space filling function. It exerts turgor pressure on the cell thus giving it its structure and shape. Contractile vacuoles provide volume to protists. They expand as water enters the cell and then expel it from the cell thus maintaining its volume. Another function of vacuoles are degradation in food vacuoles. They contain digestive enzymes that break down macromolecules or sometimes in the case of macrophages, break down harmful bacterial cells.
What are peroxisomes and their function?
Peroxisomes catalyze chemical reactions involving the addition or subtraction of hydrogen or oxygen atoms.. Peroxisomes break down molecules that do not produce harmful free radicals. The break down things into water and oxygen gas. They are also involved in the metabolism of fats and amino acids. Glyoxysomes contain enzymes that are needed to convets fats to sugars to be used by seeds. (Fats have higher energy content then carbohydrates which makes them smaller and less heavy). They are made by defusing from the ER, binding with each other and the addition of proteins and lipids matures the peroxisome and then it divides again into two mature peroxisomes.
What is the plasma membrane and its function?
The plasma membrane provides a boundary between a cell and the extracellular environment.It is selectively permeable and only allows certain substances in and out. Proteins are embedded into the plasma membrane: these provide cell adhesion, membrane transport, and cell signaling. Cell adhesion holds cells together, membrane transport allow the transport of substance in and out of the cell and acts as a receptor to enzymes that activate a cellular response. For example insulin binds to receptors which signals the cell to uptake more glucose. Cell adhesion allows cells to recognize each other and function as multicellular organism.
What are semi-autonomous cells?
The mitochondria and the chloroplast. They still depend on things from other cells, for example the mitochondria needs proteins from the cytosol. They can grow and divide to reproduce themselves. They also contain their own DNA.
What is the mitochondria and what is its function?
It is a double membrane bound organelle. The primary role of mitochondria is to provide the cell with ATP. Although they do not make energy, they convert the energy in macromolecules into an energy that can be readily used by cells, ATP. They are involved in the synthesis, modification and breakdown of several types of cellular molecules like the synthesis of certain hormones using enzymes found in the mitochondria. They also generate heat in specialized fat cells known as brown fat cells. They make heating pads that help to revive hibernating animals and vulnerable young animals.
What are chloroplast and what are their function?
It is a double bound membrane organelle whose primary function is to capture light energy and use some of that energy to synthesize organic molecules such as glucose, this process is called photosynthesis.Chloroplasts have a green pigment where as chromoplasts have orange, yellow,red
What special characteristics do mitochondria and chloroplasts have?
They have their own DNA, the mitochondrial genome and the chloroplast genome. Like bacteria, they have a a single circular chromosome. Chloroplasts tend to be larger. Mitochondria and chloroplasts tend to divide by binary fission.
What are sorting/traffic signals?
Proteins that contain short stretches of amino acid sequences that direct them to their correct cellular location.
What is the function of double bound organelles?
It allows for a larger surface area so for example the mitochondria is used to make ATP and the enzymes that are used to make it are on the membrane, so the larger the membrae surface is, the more enzymes there are so more ATP is made.
Describe the protein sorting process.
Most proteins begin on the free ribosomes in the cytosol using mRNA that contain the info for polypeptide synthesis. The cytosol provides the proteins for synthesis. Usually this halts until it has bound to the ER. After this occurs, translation resumes and the polypeptide is synthesized into the ER.
What is cotranslational sorting?
Proteins that are destined for the ER, Golgi, lysosome, vacuole, plasma membrane or secretion are first directed to the ER.
What are the benefits of cotranslational sorting?
Protection from proteases.
What are the three locations that proteins can be located to?
The cytosol (lack of sorting signal), the ER (some retain ER retention signal while some have Golgi signal which are sent through vesicles. ones in the Golgi may have golgi retention signals or may go to lysosomes, plasma membrane or outside the cell via secretory vesicles),posttranslational sorting: proteins maybe synthesized in the cytosol but have signals that send them to the nucleus, mitochondria, chloroplasts or peroxisomes.
Describe cotranslational sorting
The ER signal sequence (about 6-12 amino acids that are hydrophobic near the amino terminus), is recognized by the signal recognition particle (SRP). It pauses translation SRP binds to the receptor in the ER membrane, SRP is released and translation resumes. The growing peptide is threaded into the channel.
Describe the formation of vesicles that leave the ER
Vesicle formation is facilitated by coat proteins which help the vesicle bud from the ER membrane. V-snare are incorporated into the vesicle, it varies what type depending on the cargo it carries. T -snares in the target membrane recognize the v-snare and thus fuses with the membrane releasing the contents.
Describe posttranslational sorting
After a protein has been made, chaperone keep the protein unfolded. Proteins have a matrix targeting sequence which guides it to the desired matrix, the sequence then binds to the receptor. Chaperones are then released and the protein is transferred through a tunnel. Chaperones then bind to the protein when it reaches the inside of the cell. Matrix targeting sequence is removed by enzmes and after the protein is completely threaded, it is released and folds into a three dimensional structure. Keeping it unfolded means it can go through the relatively narrow matrixes.
Describe the fluid-mosaic model
The membrane is considered fluid because lipids and proteins can move relative to each other inside the membrane.
What are the different integral membrane proteins.
Integral membrane protein which include the transmembrane protein, lipid anchored protein
What is an integral membrane protein?
It cannot be released from the membrane. The most common type is the transmembrane protein, which has one or more regions that are physically inserted into the hydrophobic region of the phospholipid bilayer. The lipid anchor protein has a lipid molecule that is covalently attached to an amino acid. The fatty acyl tails are inserted into the hydrophobic portion of the membrane.
What are the advantages of the endomembrane system?
Compartmentalization: all of the membranes allow for different environments to perform specific functions.
What are peripheral membrane proteins?
Proteins that are noncovalently bonded to integral membrane proteins by the polar head. Usually by hydrogen or ionic bonds. Removed by pH or salt concentration alteration.
How can lipids move in the bilayer (or how are they semi fluid)
They can move via 360 rotation, lateral movement and by flippase which requires ATP. Generally it is unfavorable.
What is a lipid raft?
A group of lipids that float together as a unit within a larger sea of lipids. Usually have a high amount of cholesterol.
Which is more fluid: unsaturated or saturated fatty acyls?
Unsaturated: due to the double bond, it is hard for neighboring acyls to interact thus being able to move more freely
Why is cholesterol important for fluidity?
Cholesterol makes the membrane less fluid at high temperatures like that in the body> If it is too fluid, it may leak. It makes the membrane more fluid at lower temperatures so it does not freeze and become dysfunctional.
Why do transmembrane proteins not flippase?
Because the hydrophilic regions would be in the hydrophobic region of the bilayer.
What is the role of glycosylation?
Can serve as a signal, for example, proteins destinated for lysosomes are glycosylated that is recognized by other proteins that target it from the ER to Golgi. Also plays a role in cell surface recognition especially during development. They also protect proteins in membranes from proteases.
Describe lipid synthesis
Fatty acids are activated by CoA, they are then bonded to glycerol-phosphates and then bonded to the cytosolic leaflet in the ER membrane, the phosphate is removed by an enzyme, aholine already linked to a phsophate is attached, flippase transfers some of the phospholipids to the other leaflet
Describe the lipid exchange.
Lipids made in the ER can be given to other organelles. They can diffuse laterally to the nuclear envelope, or be transported via vesicles to endomembrane organelles. Or be involved in lipid exchange, which extract a lipid from one membrane diffuse through the cell and insert the lipid into another membrane
Desscribe how transmembrane proteins are inserted into the ER membrane
If protein has a signal to be a transmembrane protein, it begins being threaded into the ER membrane and then it is cleaved. It continues being threaded and a hydrophobic transmembrane sequence is made as the polypeptide is being threaded. Then completes
What is membrane transport?
The movement of ions and molecules across biological membranes.
What is diffusion?
through a membrane.
What is facilitated diffusion?
When a substance from a region of high concentration to a region of lower concentration through a transport protein
What is the difference between active and passive transport?
Active transport requires energy because it moves things from a lower concentration to a higher concentration or against the concentration gradient. Passive transport is from a high concentration to a low concentration.
What is a transmembrane gradient?
When the concentration of a solute is higher on one side of a membrane than the other.
What is an electrochemical gradient?
a dual gradient that has both electrical and chemical components.
What does it mean when two solution are isotonic?
They have equal concentrations of solutes on both sides of the membrane.
What does it mean when a solution is hypotonic?
When the solution outside of the cell has a lower concentration of solutes.
What does it mean when a solution is hypertonic?
When the solution outside the cell has a higher concentration of solutes.
What is osmosis?
When water diffuses across a membrane from the hypotonic compartment into the hypertonic compartment.
What happens when a cell has too much water?
Cells swell and may undergo osmotic lysis because water is taken into the cell.
What happens when the cell loses too much water?
Cells undergo shrinkage (crenation) because water exits the cell.
What do transport proteins do?
provide a passageway for the mvoemt of ions and hydrophilic molecules across membranes.
What is aquaporin?
a protein channel that allows he movement of water across the membrane
What are channels?
form an open passageway for the facilitated diffusion of ions or molecules across the membrane
What are transporters?
Bind their solutes in a hydrophilic pocket and undergo a conformational change that switches the exposure of the pocket from one side of the membrane to the other side
What are the different types of transporters?
Uniporter (a single solute moves in one direction), symporter (two solutes move in the same direction), antiporter (two solutes move in different directions
What is the difference between primary active transport and secondary transport?
A primary active transport actively exports substacne against a gradient. Secondary active transport via a pump that involves the use of another gradient to drive the active transport of the desired solute.
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