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Cell Biology LO2

Ayrshire College 18/19 HNC Cell Biology LO2 - Taught by Julie

What is the Cytoskeleton? The 3D network in the Cytoplasm of a Eukaryotic Cell made up of protein filaments
List the 3 types of Protein Filament that make up the Cytoskeleton in order of their size with the smallest first Microfilament Intermediate Filament Microtubule
How big is a Microfilament? 3-6nm
How big is a Intermediate Filament? 8-12nm
How big is a Microtubule? 25nm
What is a Microfilament composed of? Two intertwined strands of a protein called actin.
Name 2 other functions of Microfilaments They help to support other cell structures such as microvilli and they also help to transport proteins within the cell, such as secretory vesicles
Describe the process of 'Treadmilling' in regards to Microfilaments Treadmilling is the removal of actin subunits at the '-' end of the filament and the recycling of these subunits to be put on the '+' end of the filament. This process allows the filament to stay the same length but move forwards.
What is an Intermediate Filament composed of? Supercoiled fibrous proteins (like a rope), which are non polar. The subunits making up Intermediate Filaments differ between cell types
Give two examples of Intermediate filament and briefly state their function Keratin strengthens the hair and nails Neurofilaments help to strengthen the axons of neurons
What is a Microtubule composed of? Alpha and Beta Tubulin form cylindrical, hollow tubes
Name three important roles of Microtubules To provide intracellular 'tracks' to transport organelles To form the Spindle fibres that pull chromosomes apart during mitosis To form cilia and flagella used for locomotion
How does the Cytoskeleton help in cell division? The Cytoskeleton, more specifically Microtubules, form spindle fibres that pull Chromosomes apart and towards the poles during mitosis
Name the 3 different types of RNA present in cells mRNA - Messenger RNA rRNA - Ribosomal RNA tRNA - Transfer RNA
What is the purpose of mRNA? To act as a template and carry the sequence information from DNA in the Nucleus to the site of Protein Synthesis in the cytoplasm
What is the purpose of rRNA? It is the component of Ribosomes on which Protein Synthesis occurs
What is the purpose of tRNA? To pick up amino acids from the Cytoplasm and transport them to the Ribosomes for assembly into polypeptides
What is transcription? The transfer of coded information from DNA in the Nucleus to the Ribosomes in the Cytoplasm
What is translation? The formation of single amino acids into a polypeptide chain
State the two parts to a ribosome and briefly state what occurs there. The large subunit is where tRNA strands are held and the small subunit is where the mRNA strands are held
What is a Codon? A group of three nitrogenous bases.
What bond joins amino acids together in a polypeptide chain? Peptide bonds
What is a signal peptide and what is its purpose? A signal peptide is a short chain of amino acids at the N-terminus of the polypeptide chain that determines the final destination of a protein. It also allows the polypeptide chain to enter the Endoplasmic Reticulum.
What are the steps in the Secretory pathway? Endoplasmic Reticulum > Golgi Apparatus > Lysosomes/Membrane
What happens to proteins synthesised by free ribosomes? They will diffuse feely and will remain in the cytoplasm for use within the cell
What happens to proteins synthesised by Ribosomes on the Endoplasmic reticulum? They will either be excreted or they will be incorporated into the cell membrane. First, they will undergo to the secretory pathway.
What is an Anchor sequence when referring to membrane bound proteins? A short sequence of amino acids in the protein that has distinct polar and non-polar regions. This will help to determine the proteins position in the cell membrane
What is a translocon, where is it found within the cell and what is its function? It is a gateway of proteins found in the membrane of the endoplasmic reticulum that allows polypeptide chains to be passed through to the lumen of the ER, where the chain is folded into its native state
State 2 things that may happen to a polypeptide chain once it has entered the lumen of the Endoplasmic reticulum It is folded into its native shape and other post-translational modifications occur
What is signal based targeting? This is when the signal peptide at the N-terminus of the polypeptide chains determines the destination of the protein.
State 2 reasons why cells need mechanism for the breakdown of proteins To correct mistakes in protein synthesis and to regulate cell activity.
Name the 3 methods of protein degradation Ubiquitination/Ubiquitin Proteasome Pathway Lysosomal Degradation Autophagic Pathway
In the Ubiquitin Proteasome Pathway, how does a proteasome recognise that a protein is for breakdown? The protein that is destined for degradation has been tagged with multiple copies of Ubiquitin
Under what conditions does ubiquitination occur? Under normal conditions when proteins are no longer needed
How many proteins does a Lysosome contain? Up to 50 lytic enzymes
When is the Autophagic pathway activated? When cells are in a state of nutrient deprivation (starvation)
What happens in the Autophagic pathway? A phagophore is formed and it engulfs a section of the cytoplasm to be degraded. It matures into an autophagosome. The inner membrane of the autophagosome enters the lysosome, where the lytic enzymes break down the autophagosomal contents.
What happens after degradation in the Autophagic pathway? The macromolecules are released into the cytoplasm to be used by the cell.
Created by: kiera.taylor
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