14-09-21 - Cells and Organelles 1 Flashcards
State the approximate size of cells (and their components)
Why they are this size?
- Most plant and animal cells 10-100µ (microns)
- Some cells can be much smaller (e.g bacteria 1-10µ)
- Chloroplast – 1.5µ
- Proteins – 5-10nm
- Lipids – 5nm
- Small molecules – 0.5nm
- Small size ensures adequate diffusion of waste products/nutrients
What are the 4 fundamental properties of cells?
- Cells are microscopic packages that act as independent units
- Cells Originate from pre-existing cells – grow and reproduce (divide)
- Cells have a finite lifetime – they die
- Cells internal processes allow them to change/adapt/respond.
What is the plasma membrane?
What does it allow cells to do?
What does it consist of?
How do plasma membranes between cells differ?
What defines function of the cell?
- The plasma membrane encloses the cells as an independent reaction container
- Cells can function as independent units because they are enclosed by a semi-permeable membrane.
- The membrane is composed of a bilayer of lipid molecules (fluid mosaic model) with added protein molecules, with hydrophilic heads facing the outside and hydrophobic tails on the inside.
- Membranes differ because of lipid/protein types.
- Proteins define function - receptors, transportes, signalling, adhesion etc.
- 1/3 proteins in a cell are plasma membrane proteins
Describe the basic structures of prokaryotes
What are the simplest and smallest prokaryotes?
How big are they?
- Appear simple without internal membranes.
- Simplest and smallest prokaryotes are bacteria (all processes in cytosol, no internal membranes, no nucleus)
- Up to a few µ in length.
What do eukaryotes contain that prokaryotes do not?
How are membrane found organelles/compartments formed?
How do they compare in size to prokaryotes?
Where are eukaryotes found?
- Eukaryotes have internal membranes, which form membrane bound organelles/compartments, and they contain a nucleus, which prokaryotes do not have.
- Eukaryotes are much bigger than prokaryotes
- Found in animal and plant cells
What is Difference between DNA in eukaryotes and prokaryotes
- Eukaryotes contain linear chromosomal DNA in the form of chromosomes
- The DNA of eukaryotes is found in a double-membrane bound nucleus (nucleus surrounded by double-membrane nuclear envelope)
- Prokaryotes contain circular chromosomal DNA in the form of a nucleoid
- Prokaryotes may also contain small circular plasmids
Give an overview of Protein synthesis in eukaryotic cells
- DNA is transcribed to produce mRNA in the nucleus (transcription)
- The nucleus is enclosed by a double membrane called the nuclear envelope.
- Mrna passes from the nucleoplasm to the cytoplasm through the nuclear envelope via holes called nuclear pores
- mRNA is decoded and proteins made on specialized factories called ribosomes (translation)
How is DNA packaged in eukaryotic cells?
What are the 2 ways DNA is packaged?
Where are the active and inactive genes found?
- DNA Is rapped around proteins called histones to form chromatin
- Chromatin is used to create chromosomes
- Chromatin is packaged in 2 ways – euchromatin (found in the middle of the nucleus) and more dense heterochromatin (found at the edge of the nucleus)
- Most active genes are found in the euchromatin, inactive genes in the heterochromatin.
What are nuclear pores?
- Nuclear pores are selective aqueous channels for transport between nucleus and cytosol (mRNA passage but also proteins in both directions).
What are ribosomes?
What are their function?
Where are they made?
- Proteins are made on specialised organelles called ribosomes.
- Ribosomes decode Mrna message and convert it to linear polypeptides (proteins).
- Nucleolus assembles newly made ribosomes at amplified ribosome genes.
Where does all protein synthesis begin?
What dictates whether a protein ends up in the cytosol/other organelle or Golgi/er?
- All protein synthesis starts in the cytosol
- First stretches of any protein destined for ER/Golgi processing are recognised by a signal sequence/peptide and the ribosome becomes bound to ER to generate Rough ER.
Where do proteins translated on free ribosomes end up?
Where do proteins translated on ribosomes bound to ER end up?
- Free ribosomes translate proteins destined for cytosol, nucleus and mitochondria
- Bound ribosomes translate proteins with specific signal sequences that are destined for RER, other membranes. and secretion.
What is a brief overview for the pathway for secretion?
- Vesicles carry cargo from RER to the Golgi
- Cargo processed and sorted in Golgi
- Vesicles containing cargo bud from Golgi and fuse with the plasma membrane
- Packages secretion leaves the cell via exocytosis
What is the difference between constitutive secretion and regulatory secretion?
What are they each regulated by?
What is an example of regulatory secretion
- Constitutive secretion is a process concerned with the function of the individual cell, and is therefore primarily regulated by the mechanism of protein production, which are intrinsic to the cell.
- Regulated secretion is related to a cell’s interactions with other cells and therefore is responsive to external stimuli.
- An example of regulatory secretion is the release of insulin after a glucose signal enters a pancreatic beta cell.
Where is the ER located?
What are the 4 functions of the RER?
- The ER is located around the nucleus
- Site of membrane synthesis (lipids and proteins)
- Modifies proteins- adds sugar chains, trims them
- Quality control e.g monitors correct folding
- Signals stress e.g when secretion is blocked/poorly folded proteins
What is the Golgi complex?
Where is it located?
What are its 3 functions?
- The Golgi is a stack of flattened sacs found close to the nucleus
- The Golgi receives the output of RER
- Modifies lipids/proteins – grows sugar chains on proteins/adds phosphate to some proteins
- Sorts and packages cargo into distinct vesicles for export to other organelles (this happens at the exit face of the Golgi)
What is exocytosis?
How does it occur?
What is an example of substances released via exocytosis?
- Exocytosis is the process by which cells move materials from within the cell into the extracellular fluid.
- Exocytosis occurs when vesicles fuse with the plasma membrane, allowing its contents to be release outside the cell.
- CO2 and water are released from cell via exocytosis.
Label this diagram of a cell
