Organelles and cellular structure Flashcards
what is the cytoplasm and what is its purpose?
where is it?
- Prokaryotic and eukaryotic cells have cytoplasm
what does it do?
- Site of numerous biochemical processes
- There is structure and order to the organisation of organelles in the cytoplasm, because of the cytoplasm
- Many biochemical intermediates are shuttled and often converted during the transition
what is it?
- Cytosol is a jelly like substance that contains many things important to biochemical reactions (molecules/resources)
- The space between organelles and endomembrane
- Protein biosynthesis
- Cytosol and cytoskeleton make up the cytoplasm
what is the cytoskeleton and what is its purpose?
- Components of the cytoskeleton are composed of protein, NOT MEMBRANE
- Cytoskeleton components act as a form of scaffolding or as structural elements within the cytoplasm of cells
- Organises cellular structures and activities, anchoring many organelles
- It is composed of three types of molecular structures
- It helps to move organelles in mitosis
- There are 3 types
- Microtubules
- Microfilaments
- Intermediate
what are the three types of cytoskeleton?
- Microtubules
- Microfilaments
- Intermediate
what are microtubules?
- Hollow tubes; walls consists of 13 columns of tubulin molecules
- 25nm with 15-nm lumen
- Tubulin, a dimer consisting of alpha tubulin and beta tubulin
- Maintenance of cell shape (compression-resisting girders)
- Cell motility (as in cilia or flagella)
- Chromosome movements in cell division is facilitated by
- Organelle movements
- Dimer: proteins made of two different sub units
what are microfilaments?
- Two intertwined strands of actin, each a polymer of actin subunits
- Actin is a protein
- 7nm
- Purposes:
- Maintenance of cell shape (tension-bearing elements)
- Changes in cell shape- in certain specialised cells it is involved in muscle contraction
- Muscle contraction
- Cytoplasmic streaming-
- Cell motility (as in pseudopodia)
- Cell division (cleavage furrow formation)
what are intermediate filaments?
- Not made of one protein, but made of fibrous proteins that are supercoiled into thicker cables
- 8-12nm
- One of several different proteins of the keratin family, depending on cell type
- Whether that is a muscle cell or a neural filament in a nerve cell
- Maintenance of cell shape (tension-bearing elements)
- Anchorage of nucleus and certain other organelles to the cytoplasm
- Formation of nuclear lamina
what is the endomembrane system? how did it originate?
A system of compartments that includes all of the membrane-bound components of the cell (including the nuclear envelope) except for the mitochondria, chloroplasts and microbodies
Involved in the making, packaging and shipping proteins and molecules
The rough ER may have formed from invaginations of ribosome-bearing plasma membrane around the early nucleus; this ER could then have evolved into the full endomembrane system
A similar mode of evolution to the nucleus
what is the ER and what is its purpose?
- Considered to be the heart of the endomembrane system
- Consists of membrane CISTERNAE that ramify through the cytoplasm, this results in internal compartments and channels
- Its dynamic in structure- constantly changing its structure and function
- Rough has ribosomes, smooth doesn’t
- The rough ER produces proteins and lipids, the smooth ER produces the majority of lipids
- They can both make carbs
- The ER provides surfaces for the synthesis of the proteins, glycoproteins, carbs and lipids
- These biomolecules are then secreted throughout the endomembrane
- Glycoprotein- protein with a sugar (typically oligosaccharides)
what is the golgi apparatus and its purpose?
Functions in the:
1. collection
2. packaging
3. distribution of molecules (many secreted)
- Consists of flattened stacks of membrane or cisternae called golgi stacks
- Golgi stacks in a cell are called golgi apparatus
- Golgi stacks are functional extensions of the ER and constantly receive vesicles from the ER.
- Golgi are polar structures.
- Vesicles arrive at the cis face (receiving) and leave the trans face (shipping)
- Polar means it has directionality, or a front and a back, not that it has a charge specifically
- Proteins, glycoproteins, and other molecules formed in the ER are transported to the Golgi apparatus in vesicles to be biologically modified
- Polysaccharides are also formed here
- Many molecules, such as hormones and digestive enzymes, exist the Golgi in secretory vesicles and then exit the cell via exocytosis
- Other molecules are packaged into vesicles such as lysosomes and remain within the cell
what are plant vacuoles and their purpose?
- The plant equivalent of lysosomes, surrounded by a single membrane called the tonoplast
- Contain hydrolytic enzymes that serve as degradative compartments
- Vacuoles also performs a diverse range of other functions
- Storage of nutrients
- Pigment storage
- Maintenance of cell turgor pressure (fill with water or loose water to expand or shrink the cell)
what are lysosomes and their purpose?
- Recycle bin of animal cells
- Surrounded by single membrane
- Break down material from endocytosis or recycle old organelles (autophagy)
- Acidic interior and approximately 40 different hydrolytic enzymes derived from the rough ER and Golgi
- Lysosomes have an internal Ph of 4.5
- They can also be used to digest pathogens that enter the cell
what are microbodies and their purpose?
- Another recycle bin found in both plant and animal cells
- Similar in size to a lysosomes and also surrounded by a single membrane, but contains enzymes derived from free ribosomes in the cytoplasm (not ER) therefore not a part of the endomembrane system
- Neutral pH; contain oxidative enzymes that generate hydrogen peroxide and the enzyme catalase to break down hydrogen peroxide
- Two types:
- Peroxisomes (break down amino acids)
- Glyoxysomes (break down fatty acids)
things to remember about membranes
- They always enclose a space- a cisterna or vesicle
- Membranes are never open-ended, unless the cell is damaged
- Membranes have the consistency of olive oil in water- not stiff barriers as indicated in diagrams
what are phospholipids and what is their importance in biology?
- Phospholipids comprises the largest component of all biological membranes
- Only two fatty acid chains attached to glycerol, its third C is attached to a phosphate group (ester), which is negatively charged and hydrophilic
- Therefore one part of phospholipids is hydrophobic (the fatty acid tails) and another part is hydrophilic (the phosphate head)
- Non polar fatty acid chain
- Charged polar head- negatively charged phosphate and positively charged choline, sometimes
- Electrostatic dipole interactions of the head
- Non-polar tails hydrophobic interactions like dispersion forces
- The phospholipid bilayer is fluid- hence the fluid mosaic model
- Phospholipids move laterally- side to side
- Molecules/atoms can then move in and out
what is the plasma membrane and its purpose?
- The phospholipid bilayer, with the two groups of tails sandwiches towards the interior, one group of Phosphate heads towards the cytoplasm (aqueous), other towards the cell’s exterior (aqueous)
- Role: prevents free flow of liquids into/out of cells due to the hydrophobic middle later, and protects cell’s interior
- The phospholipids are mobile: the move laterally all the time, along the plane of the membrane. Have to be fluid to function
- Cholesterol is present in all membranes and reduces fluidity.
- Cholesterol polar head- largely non-polar body. Non-polar 4 ring structure disp. forces with fatty acid beside it. Polar head- hydroxyl groups for dipole-dipole or ion-dipole with head. Allows to become less fluid and fatty acid closer together
- Plasma membranes are selectively permeable, regulating the molecular traffic
- Hydrophobic (non-polar) molecules, such as hydrocarbons, can dissolve in the lipid bilayer and pass through the membrane rapidly
- Polar molecules, such as sugars, do not cross the membrane easily
