eurkaryotic cell structure and function Flashcards
(29 cards)
What are the three points of the cell theory?
- All living organisms are composed of one or more cells.
- The cell is the most basic unit of structure in all organisms.
- All cells arise only from pre-existing cells.
Why is there a need to keep cell size small?
As the size of the cell increases, the surface area to volume ratio decreases. The number of chemical exchanges that could be performed with the extracellular environment
would be inadequate to maintain the cell, because most of its cytoplasm is relatively far from the outer membrane. Exchange with the extracellular environment is vital as substances like oxygen and nutrients can only enter the cell, and waste products can only leave, in this fashion.
Describe the cytosol
aqueous solute rich matrix (the soluble part of the cytoplasm) that appears transparent and lacking structure. 90% water and contains various essential ions and soluble organic molecules such as sugars and amino acids, soluble proteins including enzymes and the cytoskeleton
What is the cytoskeleton
a network of fine strands of globular and fibrous proteins, which provides structure and support to the cell
Describe and explain the advantages to having membranous organelles
allows the maintenance of
characteristic differences between the contents of each organelle and the cytosol. The compartmentalisation of specific reactions provide different local environments for which incompatible processes can occur simultaneously.
increase membrane surface area, allow for embedding of enzymes and proteins, increasing efficiency of reactions by providing optimal enzyme concentration
Which organelles have a double membrane
Nuclear envelope, mitochondria and chloroplasts
What is the function of the nucleus?
Encloses genetic material and protects DNA from metabolically active cytoplasm
How does the structure of the nuclear envelope relate to its function?
It is a double membrane that separates the contents of the nucleus from the cytoplasm. It is perforated by nuclear pores, allowing macromolecules like mRNA and rRNA to exit the nucleus, proteins like enzymes to enter and exit the nucleus.
What is the nucleoplasm composed of?
An aqueous matrix containing proteins, metabolites, ions, RNA and chromatin. Chromatin can be loosely coiled (euchromatin), tightly coiled (heterochromatin).
Explain the significance of the nucleolus in protein synthesis.
The nucleolus is composed of DNA carrying rRNA genes, RNA and proteins. This functions to synthesise rRNA which forms a component of ribosomes, which subsequently helps to synthesise proteins during translation.
Describe the structure of the ER and relate this to its function.
It is an extensive network of hollow membranous sacs or sheets (cisternae) — increases membrane surface area for synthesis, hollow to accommodate newly synthesised substances
What is the function of the rER?
rER-bound ribosomes are sites of protein synthesis and enters the rER lumen, where proteins are folded into their native, specific 3D conformation, destined for export or targeted to various cellular organelles
What are the functions of the sER?
- Synthesis of lipids (including hormones)
- Metabolism of carbohydrates
- Detoxification of drugs and poisons (thus is abundant in liver cells)
- Storage of calcium ions for use in muscle contraction and cell signalling
Describe the structure of the Golgi apparatus in relation to the processes that happen with it.
It is a stack of flattened, membrane-bound sacs called cisternae, with a cis face and trans face.
New cisternae are constantly formed at the cis face by receiving transport vesicles from
the ER. The membranes of transport vesicles from the ER fuses with the cis face membrane and deposit their contents into Golgi cisternal space.
● At the trans face, membranes bud off to form secretory vesicles, which contain materials to
be transported to the extracellular matrix/to form lysosomes.
● Between the Golgi sacs, Golgi vesicles transfer materials between parts of the Golgi.
● Some Golgi vesicles also bud off from the trans face to transport substances to other
organelles in the cell.
What is the function of the Golgi apparatus?
It is the site of modification and packaging of ER products. Some modifications include glycosylation (addition of sugar groups) and trimming (removal of
excess monomers). ER products are progressively modified as they move through the stacks of the Golgi complex
What is the significance of GA in cells active in secretion?
abundant flattened cisternae provide increased surface area for vesicle reception and budding.
Multiple cisternae also allow for different modification processes to occur simultaneously.
What is the structure of the lysosome?
The lysosome is a membranous organelle that appears homogenously electron-dense under the EM. It contains hydrolytic enzymes that can digest most biological macromolecules.
Describe the three major functions of the lysosome.
- Digestion of materials taken into cells — food particles engulfed by endocytosis to form food vacuoles OR phagocytosis
- Autophagy of worn-out organelles — fusion of vesicle with damaged/unknown structures or organelles
- Autolysis — mass release of lysosome triggers autolysis/apoptosis leading to destruction of cell
Describe the structure and function of the vacuole in plant cells.
Large central vacuole surrounded by a single membrane
known as a tonoplast.
1. Storage of organic compounds and inorganic ions
2. Disposal site for toxic metabolic by-products
3. Contains pigments
4. Plant protection by accumulating compounds that are toxic or unpalatable to consumers
5. Cell growth and elongation as water accumulates in the vacuole
Describe the membranes of the mitochondrion and relate this to its function.
The outer membrane is smooth, but the inner membrane is highly convoluted with cristae to increase the surface area for the attachment of various enzymes involved in aerobic respiration.
What is the general function of the mitochondrion?
It is the site of aerobic/cellular respiration, synthesising ATP molecules during cellular/aerobic respiration.
What is the purpose of the mitochondrial matrix?
houses enzymes, circular DNA, RNA and ribosomes so the mitochondria can synthesise its own proteins/site of the Krebs cycle. The compartmentalisation of the mitochondrial matrix sets up a proton gradient across the inner mitochondrial membrane, as the inner mitochondrial membrane is impermeable to protons.
What is the function of chloroplasts?
The sites of photosynthesis — They
convert solar energy to chemical energy by absorbing sunlight, and use it to drive the synthesis
of organic compounds from carbon dioxide and water.
Describe the structure of chloroplasts
They are lens-shaped and are surrounded by the chloroplast envelope. The inner membrane encloses the stroma containing enzymes required for light-independent reactions and circular DNA that enables synthesis of chloroplast proteins. A third set of membranes are the thylakoids enclosing the thylakoid lumen. They stack up together to form thylakoid discs, which are stacked up to form grana that are connected by intergranal lamellae. This increased surface area increases surface area for attachment of chlorophyll and other photosynthetic pigments. Compartmentalisation of thylakoid lumen also sets up a proton gradient across thylakoid membranes, since thylakoid membranes are impermeable to protons.
