1.2 Ultrastructure of Cells Flashcards
What is resolution?
Making separate parts distinguishable.
Which is better light or electron microscopes?
Electron microscopes have a much much higher resolution. Light microscopes are limited by the wavelength of light, you cannot focus it past a certain point. Electron microscopes use beams of electrons which have a much smaller wavelength.
What are prokaryotic cells like?
They have a simple structure without compartments. They do not have a nucleus. They were the first organisms to develop on earth and have a very simple structure. They have a cell wall containing peptidoglycan. One uninterrupted chamber of cytoplasm. Ribosomes 70S. DNA in a circular molecule, but not associated with proteins so looks lighter compared to areas containing ribosomes, it is called the nucleoid and will appear white on a drawing.
They divide by binary fission, asexual reproduction. The DNA molecule replicates, and moves to each end of the cell, then the cell splits in half quickly after.
What does a prokaryotic cell wall contain?
Made of peptidoglycan
How do prokaryotic cells multiply?
By binary fission, asexual reproduction. The DNA molecule replicates, and moves to each end of the cell, then the cell splits in half quickly after.
What are Eukaryotic cells like?
They are compartmentalised. They have a nucleus and organelles which are compartments in the cell’s cytoplasm.
What are the advantages to being compartmentalised?
- Enzymes and substrates for particular processes can be much more concentrated.
- Substances that could be damaging to the cell can be kept inside the membrane of an organelle. For example the digestive enzymes of a lysosome.
- pH can be optimal for a particular process
- Organelles, with their contents, can be moved around the cell.
What is the nucleus?
The nuclear membrane is double and has pores through it. The nucleus contains chromosomes consisting of DNA associated with histone proteins. Uncoiled chromosomes are spread throughout the nucleus and called chromatin.
DNA is replicated here and transcribed to form mRNA, which is exported via the nuclear pores to the cytoplasm.
What is chromatin?
Uncoiled chromosomes.
What does the rough endoplasmic reticulum do?
The rER consists of flattened membrane sacs, called cisternae. Attached to the outside are ribosomes (80S). The main process of the rER is to synthesise protein for secretion from the cell. Protein synthesised by the ribosomes passes into its cisternae and is then carried by vesicles, which bud off and are moved to the Golgi apparatus.
What does the Golgi apparatus do?
This organelle consists of flattened membrane sacs called cisternae, like rER. However the cisternae are not as long and are often curved, do not have attached ribosomes and have many vesicles nearby. The Golgi apparatus processes proteins brought in vesicles from the rER. Most of these proteins are then carried in vesicles to the plasma membrane for secretion.
What do lysosomes do?
These are approximately spherical with a single membrane. They are formed from Golgi vesicles. They contain high concentrations of protein, which makes them densely staining in electron micrographs. They contain digestive enzymes, which can be used to break down ingested food in vesicles or break down organelles in the cell or even the whole cell.
What do Mitochondria do?
A double membrane surrounds mitochondria, with the inner of these membranes invaginated to form structures called cisternae. The fluid inside is called the matrix. The shape of mitochondria is variable but it usually spherical or ovoid. They produce ATP for the cell by aerobic respiration. Fat is digested here if it is being used as an energy source in the cell.
What do free ribosomes do?
These appear as dark granules in the cytoplasm and are not surrounded by a membrane. They have the same size ribosomes attached to the rER. They are known as 80S. They synthesise protein, releasing it to work in the cytoplasm, as enzymes or in other ways. Ribosomes are constructed in a region of the nucleus called the nucleolus.
What do chloroplasts do?
A double membrane surrounds the chloroplast. Inside are stacks of thylakoids, which are flattened sacs of membrane. The shape of chloroplasts is variable but usually spherical or ovoid. They produce glucose and a wide variety of other organic compounds by photosynthesis. Starch grains may be present inside if they have been photosynthesising rapidly.
