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HNC Cell Biology

LO2

QuestionAnswer
Where in the cell does protein synthesis take place? in the ribosomes
Where are proteins destined for the use in the cytoplasm of the cell made? Proteins that are to be used in the cytoplasm are made on the free ribosomes
Where are proteins destined for the membranes of the cell made? Membrane proteins are made on the ribosomes found on the rough endoplasmic reticulum
Give examples of proteins made on free ribosomes? cytoskeleton proteins, intracellular enzymes
Give examples of membrane proteins made on ribosomes associated with rough endoplasmic reticulum? ion channels, peptide hormone receptors (insulin receptor)
Where are proteins destined for secretion out of the cell made? Proteins destined for excretion out of the cell are made on the ribosomes found on the rough endoplasmic reticulum
Give examples of proteins destined for excretion made on ribosomes associated with rough endoplasmic reticulum? antibodies, some bacterial toxins, extracellular enzymes
What happens in rough ER during protein translation? In the lumen of RER, protein folds as it is made by the ribosome with a help of chaperone proteins.
What can happen to protein in rough ER after it is synthesised? Protein can undergo post-translational modifications.
How are proteins directed to the correct cellular membrane destination? Proteins have a 20 amino acid tag attached to the N-terminus end that allows them to be directed to correct destination via secretory pathway
What is a secretory pathway? Secretory pathway is a continuous trafficking of membrane vesicles going from ER to Golgi body to the cell membrane/lysosomes
What is an autophagic pathway? Autophagic pathway is a pathway responsible for the degradation of cellular components such as abnormal proteins, excess or damaged organelles, or macromolecules
When is the autophagic pathway activated? Autophagic pathway is activated when a cell is in a state of nutrient deprivation (starvation)
What is the purpose of autophagic pathway? Purpose of autophagic pathway is to enable the cell to recycle macromolecules for nutrition when nutrients are scarce.
How does autophagic degradation start? Autophagic degradation starts with formation of double membrane cup shaped structure called phagophore.
In autophagic degradation what does a phagophore do? Phagophore encloses a section of cytoplasm containing material to be degraded (macromolecule or a whole organelle)
In autophagic degradation what happens after the phagophore enclosed a section of cytoplasm containing material to be degraded? Phagophore elongates and matures into autophagosome (this isolates the material to be degraded from the rest of cytoplasm)
In autophagic degradation what happens after autophagosome is formed? Autophagosome fuses with a lysosome and the contents of autophagosome is degraded.
In autophagic degradation what happens to the contents of the autophagosome after degradation is complete? Digested macromolecules are released into cytoplasm for re-use.
What is a lysosome? lysosome is a single membrane bound organelle containing a mixture of digestive enzymes (proteases and lipases)
What are the three pathways for protein degradation in cells? Ubiquitin proteasome pathway, Lysosomal degradation pathway, Autophagic degradation pathway
How are proteins directed for degradation by ubiquitin proteasome pathway? Proteins that are to be degraded are tagged by addition of a number of units of a small protein called ubiquitin
In ubiquitin proteasome degradation pathway what happens after proteins are tagged with ubiquitin? Poly-ubiquitinylated proteins are targeted to a multiprotein complex called a proteasome which degrades them into amino acids.
What happens during lysosomal degradation pathway? Components to be degraded (individual proteins but also whole organelles) engulfed by the lysosome and digested. Broken down macromolecules are released into cytoplasm
Why do cell need to degrade proteins? if the protein is damaged, if the proteins is no longer needed, to release energy from degradation of proteins if carbohydrate isn’t available, to reuse amino acids to make new proteins
What type of macromolecule is cytoskeleton made from? protein
What are the three main cytoskeleton types in eukaryotic cell? microfilaments, intermediate filaments, microtubules
What is the size of microfilaments? Name an example of a microfilament. 3-6nm, actin is an example of a microfilament
Which cytoskeleton types are polar? What does this mean? microfilaments and microtubules are polar. They have an end where the subunits are preferably added and an end from which they are removed.
What is the name of a process by which amoeba use cytoskeleton to move? How does this work? Treadmilling. Subunits are added to +ve end of actin and removed from a -ve end. Filament stays the same length but moves forward.
List functions of actin in non muscle cells. actin supports microvilli, and help transport vesicles around the cell by providing a track for motor proteins to move on
Name the largest type of filament making up cytoskeleton and state its size Microtubule, 25nm accross
What are the subunits of the largest filament type called and how are they organized? Subunits of microtubules are called Tubulin. There is alpha and beta tubulin and they form a heterodimer. Heterodimers come together to make a hollow tube.
What are the functions of microtubules? Microtubules help to transport organelles within the cell. They form spindle fibres that separate chromosomes during mitosis and form flagella and cilia in eukaryotes
What is the size of intermediate filaments and in what type of cells are intermediate filaments especially common? 8 – 12 nm in diameter, found in cells that need to withstand a lot of stress such as epithelial or nerve cells
What are the functions of cytoskeleton? provides structural support to maintain the shape of the cell, acts as internal framework for positioning organelles, moves materials and organelles within the cell, separates chromosomes during cell division.
What is Rough endoplasmic reticulum? Double membrane bound organelle, continuous with nuclear envelope with ribosomes transiently attached on its surface.
What does Rough endoplasmic reticulum do? Makes proteins destined for membranes, used in lysosomes or secreted from the cell
What is Smooth endoplasmic reticulum? Double membrane bound organelle, continuous with RER and nuclear envelope, without ribosomes attached on surface Makes: lipids, phospholipids and steroids.
What does Smooth endoplasmic reticulum do? Makes: lipids, phospholipids and steroids
What is Golgi apparatus? A series of flattened single membrane sacs (cisternae), not continuous with RER and nuclear envelope
What is the function of Golgi apparatus? Sorts proteins coming from RER (cis face), stores and modifies them and sends them on (trans face) to final destination (plasma membrane, organelles etc..)
What are the two steps in protein synthesis? Transcription and Translation
What is transcription? Process of copying information in DNA to make mRNA
Where does transcription take place? Transcription takes place in the nucleus
What is translation? Process of converting information contained in mRNA into a protein
Where does translation take place? Translation takes place on the ribosomes
Where are ribosomes found? Floating freely in the cytoplasm or associated with rough endoplasmic reticulum
What happens to mRNA after transcription is complete? mRNA travels through nuclear pore to the ribosome (made from rRNA) where it is sandwiched between two subunits. Information it carries is translated into protein with the help of adapter molecule called tRNA
What is the role of tRNA? tRNA carries an amino acid at one end and has an anticodon on the other end. When two tRNAs are bound to mRNA side b yside amino acids at the opposite end of an anticodon can be joined by a peptide bond
Created by: dr.prorocic
 

 



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