L7 - Cell Organelles Flashcards
What does the cytoplasm contain?
All the cellular components between the plasma membrane and the nucleus.
What 2 components does the cytoplasm contain, and what are the roles/functions of these components?
- Cytosol (intracellular fluid)
- Organelles (specialised structures which cooperate to maintain homeostasis)
What is cytosol the site of?
A wide range of enzymatically controlled reactions.
How much of a cell’s total volume does cytosol make up?
55%
What does cytosol contain? (x6)
- Dissolved Ions
- Glucose
- Amino Acids
- ATP
- Lipids
- Waste Products
What do the different components of a cytoskeleton work in unison to provide?
Support and functionality
What are the thinnest components of the cytoskeleton?
Microfilaments
What are microfilaments responsible for?
Internal movements within the cell
What are microfilaments made of?
- Actin
- Myosin
What are intermediate filaments made of, and how are they arranged?
Fibrous proteins organised into tough, rope-like assemblies (e.g. keratin)
What are the functions of intermediate filaments?
- Stabilise a cell’s structure
- Help maintain its shape
What are the thickest components of the cytoskeleton?
Microtubules
What are microtubules responsible for?
- Cell structure
- Cell motility
What are microtubules filaments made of, and how are they arranged?
Long, hollow cylinders made up of many molecules of the protein tubulin.
What are the two subunits of tubulin?
- α-tubulin
- β-tubulin
What three types of movement do microfilaments help generate?
- Contraction
- Locomotion
- Cell Division
What are the functions of microfilaments?
- Help generate movement
- Provide mechanical support needed for cell strength and shape
- Create microvilli
Where are intermediate filaments found?
In parts of the cell subject to mechanical stress.
Provide 3 examples of intermediate filaments.
- Keratin
- Vimentin
- Lamin
Describe the formation of microtubules.
1) Form in centrosome
2) Then radiate outwards
What are the functions of microtubules?
- Help with cell strength, shape and movement of organelles (e.g. vesicles) and with cell division
- Help provide structure to flagella (e.g. spermatozoa)
Which cell organelle is the centrosome found near?
Nucleus
What does the centrosome serve as?
- Main microtubule organising centre
- Regulator of cell cycle progression
How many centrioles does the centrosome consist of?
2
Describe the structures of the 2 centrioles within the centrosome.
- Cylindrical structures composed of a circle of 9 clusters of microtubule triplets
- Pericentriolar material surrounds the centrioles and consists of numerous rings of tubulin
(Both at right angles to each other)
What are the functions of the centrosome?
- Aid the growth of mitotic spindle during cell division
- Maintain equal distribution of chromosomes in daughter cells
What are cilia primarily made from?
Microtubules
What are cilia?
Motile, short hair-like projections on the cell surface
Describe the structure of a cilium.
Each cilium is anchored to a basal body and has a core of microtubules enclosed in a membrane
What is the function of cilia?
To transport fluid along a cell’s surface.
Describe the effect of smoking on cilia.
- Smoking destroys the cilia
- Resulting in a build-up of mucus, dust and bacteria within the lungs
- Must be removed by persistent coughing
What role does cilia play in the female reproductive system?
Cilia passes the oocyte towards the uterus.
What does smoking increase the risk of, in females?
Ectopic pregnancy
Describe two ways in which flagella is different from cilia.
- Flagella are much longer
- Often only one flagellum is found on a cell
Describe the structure of the endoplasmic reticulum.
Network of membranes in the form of flattened sacs and tubules, extending form the nuclear envelope into the cytoplasm.
What are the two types of endoplasmic reticulum?
- Rough ER
- Smooth ER
What is attached to the surface of the rough ER?
Ribosomes
What happens to proteins made by ribosomes, once they enter the ER space?
They are processed and sorted.
What two things may enzymes in the rough ER do?
- Attach carbohydrate groups
- Attach proteins to phospholipids
What can happen to molecules that are packaged and sorted in the rough ER?
- May be incorporated into membranes of organelles / plasma membrane
- May be secreted via exocytosis
Where is the smooth ER found?
Smooth ER extends from the rough ER.
Describe the differences between the smooth ER and rough ER.
Smooth ER contains no ribosomes but has a greater range of enzymes; making its functions more diverse.
What does the smooth ER do?
- Synthesises fatty acids and steroids such as oestrogen / testosterone.
- Helps release glucose from gluc-6-p in the liver
- Detoxifies lipid soluble drugs such as alcohol / pesticides
- Stores Ca2+ ions in muscle
What happens to individuals who repeatedly take drugs such as the sedative, phenobarbital?
They develop changes in the smooth ER in their liver cells: Cells produce more smooth ER to counteract the poison; meaning the person has to take more of the drug to feel the effect.
Describe the structure of a ribosome.
Consist of a large subunit and small subunit synthesised separately in the nucleolus.
What are ribosomes rich in?
Ribosomal RNA (information)
How many proteins do ribosomes contain?
Over 50 proteins each
Where are ribosomes found?
Ribosomes are present free in the cytoplasm, within the mitochondria or attached to the endoplasmic reticulum.
What is the function of ribosomes?
Sites of protein synthesis
Where are most proteins from the rough ER transported to?
Other regions of the cell, including the Golgi complex
Describe the structure of the Golgi apparatus.
Consists of 3 - 20 membranous cisternae (sac-like structures) with bulging edges arranged in a stack
Describe the two faces of the Golgi complex.
- Cis / entry face faces the ER
- Trans / exit face faces the plasma membrane
Describe how the Golgi Complex processes and packages.
1) Transport vesicles containing polypeptide bud off of smooth ER
2) They fuse with the cis face of the Golgi apparatus, releasing polypeptide into the lumen of the Golgi apparatus
3) The transport vesicle emerges from the trans face of the Golgi apparatus
4a) It is either enclosed in a secretory vesicle and the polypeptide is released from the vesicle by exocytosis into the extracellular fluid
4b) Or the vesicle emerging from the trans face becomes a lysosome
4c) Or the vesicle emerging becomes a membrane protein and is inserted into the plasma membrane
What are the functions of lysosomes?
- Digestion of substances entering the cell
- Digestion of worn out organelles (autophagy) and entire cells (autolysis)
What is autophagy required for?
- Renewal
- Cellular differentiation
- Control of growth
- Tissue remodelling
Describe the steps of autophagy.
1) Vesicle Nucleation: Formation of an isolation membrane
2) Vesicle Elongation
3) Autophagosome is formed
4) Outer membrane of the autophagosome fuses with an endosome = forming an amphisome
5) Docking and Fusion: The amphisome fuses with a lysosome, forming an autophagolysosome
6) Vesicle Breakdown and Degradation: Material is degraded inside the autophagolysosome
What is Tay-Sachs Disease?
An inherited disease affecting children, that often causes death before the age of 5
What causes Tay-Sachs Disease?
Mutation of the lysosomal enzyme, HexA
What effect does the mutation of the lysosomal enzyme, HexA have during Tay-Sachs Disease?
HexA normally breaks down a glycolipid called ganglioside GM2, especially prevalent in nerve cells.
In the absence of HexA, the glycolipid builds up, destroying nerve cell function.
What are the symptoms of Tay-Sachs Disease?
- Seizures
- Muscle rigidity
- Blindness
What are peroxisomes?
Organelles containing oxidases - similar to lysosomes but a lot smaller
What are peroxisomes involved with?
Amino acid and fatty acid metabolism
What are the roles of peroxisomes?
- Oxidise toxic substances such as alcohol (high copy number in the liver)
- Contain enzyme catalase to protect against toxic effects of hydrogen peroxide (made in oxidation reactions)
Describe peroxisomal disorders.
- Form a heterogenous disease group, with different degrees of severity
- Metabolic diseases that share dysfunction of peroxisomes
- Lead to brain disorders and affect respiratory functions
Provide 3 examples of peroxisomal diseases.
- Zellweger Syndrome (ZS), which is usually fatal within the first year of life
- Neonatal Adrenoleukodystrophy (NALD), which is usually fatal within the first 10 years
- Rhizomelic Chondrodysplasia Punctata (RCDP), which in its most severe form is fatal within the first year or two of life
Describe the degradation of lysosomes and proteasomes.
- Lysosomes degrade proteins delivered in vesicles
- Proteasomes degrade ‘free’ cytosolic proteins (unneeded, damaged or faulty)
What process are proteasomes important in?
In negative feedback (they switch off a pathway once a response has been achieved)
What do proteasomes contain?
Protease enzymes
What is Alzheimer’s Disease caused by?
The build-up of misfolded proteins in brain cells. (Ongoing research into why these proteins are not degraded - possibly caused by proteasome dysfunction)
What are mitochondria?
Site of aerobic respiration (convert glucose to produce energy) - Known as cell’s ‘Powerhouse’ / ‘Energy Converters’
How many mitochondria do cell’s have?
100 - 1000s (depending on function)
What are the other functions of mitochondria?
- Cell growth
- Cell signalling
- Cell differentiation
- Cell death
What does the cristae of the mitochondria provide?
A massive surface area for respiration
Where are the enzymes needed for respiration found in the mitochondria?
- In the matrix
- On the cristae
State the 5 parts of a mitochondrion and describe their roles.
- Intermembranal Space
- Small space to quickly accumulate protons
- Inner Membrane
- Contains ETC and ATP synthase for oxidative phosphorylation
- Matrix
- Has appropriate enzymes and a suitable pH for the Krebs cycle
- Cristae
- Highly folded so as to increase SA:Vol ratio
- Outer Membrane
- Contains transport proteins for shuttling pyruvate into mitochondrion
Describe the structure and shape of a nucleus.
- Spherical / oval shaped (most cells only have one)
- Surrounded by a double membrane (nuclear envelope)
- Many nuclear pores extend through the envelope (channels for ions, active transport for RNAs and proteins)
- In the centre, spherical bodies called nucleoli are present
What are nuclei?
Clusters of proteins, DNA and RNA; responsible for producing ribosomes
What is transcription?
The process of constructing a messenger RNA molecule using a DNA molecule as a template with resulting transfer of genetic information to the messenger RNA.
Where does transcription take place?
In the nucleus
Where does translation take place?
In the rough ER / cytoplasm
Describe the stages of transcription.
1) DNA separates into 2 complementary strands
2) mRNA makes a copy of the DNA code
Describe the stages of translation.
(mRNA leaves the nucleus through the nuclear pores)
3) mRNA binds with a ribosome at the start codon
4) The ribosome reads the codons and assembles the amino acids in order
5) tRNA brings the amino acids for the polypeptide
6) The stop codon releases the polypeptide and ribosome
