2.1 Cell Structure Flashcards
Example of prokaryotes
Bacteria
Examples of eukaryotes
Animals, plants, fungi, algae
How do prokaryotic cells divide?
Binary fission
How do eukaryotic cells divide?
Mitosis
What are the organelles found in plant cells but not animal cells and what are they made of?
- Vacuole (cell sap)
- Chloroplasts
- Cell wall (cellulose)
All cells walls are made of cellulose except for…
Fungal cell walls which are made of chitin.
What is the plasma membrane made from?
A phospholipid bilayer
What is a phospholipid made from?
A phosphate group, a glycerol molecule and two fatty acids.
What is the function of the plasma membrane?
Controls passage of organic molecules. E.g. ions, water etc.
What is the structure of the nucleus?
- Double membranes nuclear envelope with numerous pores.
- Nucleoplasm is semi-solid liquid inside the nucleus where chromatin and nucleolus are found.
- Contains linear chromosomes made up of DNA.
What is the function of the nucleus?
- Controls actions of cell
- DNA in nucleus contains instructions for protein synthesis
What is the function of the nucleolus?
rRNA is joined with proteins to form ribosomal subunits.
Structure of mitochondria
Mitochondria are oval-shaped, double-membrane organelles that have their own ribosomes and DNA.
Each membrane is a phospholipid bilayer embedded with proteins.
The inner layer of the membrane has folds called cristae.
The area surrounded by the folds is called the mitochondrial matrix.
Structure of chloroplasts
Chloroplasts have their own DNA, ribosomes and have inner and outer membranes.
The space enclosed by the inner membrane contains a set of interconnected and stacked fluid-filled membrane sacs called thylakoids.
Each stack of thylakoids is called a granum (plural = grana).
Grana are linked by lamellae.
Lamellae are flat, thin parts of thylakoid membrane.
The fluid enclosed by the inner membrane that surrounds the grana is called the stroma.
Structure of Golgi apparatus
The Golgi apparatus is a series of flattened membranous sacs.
Function of Golgi apparatus
Transport vesicles form at the endoplasmic reticulum and fuse with the Golgi apparatus.
The transport vesicles empty proteins and lipids into the lumen of the Golgi apparatus.
As the proteins and lipids travel through the Golgi, they are sorted, packaged and tagged so that they can be sent to the right place.
Structure of Golgi vesicles
Golgi vesicles are membrane-bound, fluid-filled vesicles located in the cytoplasm.
They are small, round and are seen in a high density near the edges of the sacs.
Lysosomes are a type of Golgi vesicle.
Function of Golgi vesicles
Golgi vesicles store and transport modified proteins and lipids from the Golgi apparatus to target cells.
Lysosomes are a special type of Golgi vesicle. They contain enzymes called lysozymes.
Lysozymes aid the breakdown of proteins, polysaccharides, lipids, nucleic acids and old organelles.
Structure of ribosomes
Made of rRNA and protein. Don’t have a membrane
Function of touch endoplasmic reticulum
Has ribosomes so protein synthesis
Function of smooth endoplasmic reticulum
Makes and processes lipids.
Structure of cell vacuoles
Surrounded by a membrane called the tonoplast and contain a weak solution of salts and sugars called cell sap.
Function of vacuoles
The central vacuole allows the cell to remain rigid.
When the central vacuole holds more water, the vacuole pushes against the cell wall and pressure is maintained. This stops the plant from wilting.
What is DNA like in prokaryotes
Prokaryotic DNA is found as a circular molecule in the cytoplasm.
Some prokaryotes have smaller loops of DNA called plasmids that are not part of the main circular DNA molecule.
Prokaryotes vs eukaryotes
Cell membrane made of murein in prokaryotes and phospholipids in eukaryotes.
Smaller ribosomes in prokaryotes.
Prokaryotes don’t have a nucleus, mitochondria, Golgi and any other membrane bound organelle.
Prokaryotes have a capsule
Describe the process of binary fission
1) DNA and plasmids replicate
2) Genetic material migrates towards opposite poles
3) Cytoplasm begins to divide
4) 2 genetically identical daughter cells with identical DNA loop but a variable number of plasmids
Structure of viruses
Viruses are made up of nucleic acids.
The nucleic acids are surrounded by a protein called a capsid.
Have attachment glycoproteins that bind to complementary receptors on host cells.
What are the two steps of cell fractionation
1) Homogenisation
2) Ultracentrifugation
Describe homogenisation
The tissue sample is homogenised using a blender to break the cell membranes open
What are the necessary conditions for homogenisation?
Ice cold (reduces enzyme activity that might damage organelles).
Isotonic solution (prevents osmosis that could shrink or burst organelles).
No osmosis takes place in isotonic solution.
Buffered solution (keeps pH constant and avoids damaging the protein structures).
What must be done between homogenisation and ultracentrifugation?
Filtration to remove excess cell debris
Describe the process of ultracentrifugation
The samples are spun at a low speed in a centrifuge.
Heavier organelles are forced to the bottom of the tube.
Lighter organelles move towards the top.
Cell debris (e.g. cell walls) forms a pellet at the bottom of the tube, leaving the supernatant (a liquid) above it that contains the organelles.
The supernatant is poured off and centrifuged at a higher speed to separate the next heaviest organelles (the nuclei).
This is repeated at increasingly higher speeds to separate each fraction.
What is the order of fractionation from heaviest to lightest?
Nucleus.
Chloroplasts.
Mitochondria.
Lysosomes.
Endoplasmic reticulum.
Ribosomes.
How do optical microscopes work and can the specimens used be alive?
Visible light passes and is bent through the lens system to enable the user to see the specimen.
The specimen can be alive.
How does a transmission electron microscope work and what are some features of it?
In a TEM, the electron beam penetrates the cell and provides details of a cell’s internal structures.
TEMs use electromagnets to focus the electron beam.
TEMs are high resolution microscopes.
In thin specimens, you can see the internal structures of organelles such as chloroplasts.
How does a scanning electron microscope work and what are some features of it?
In a SEM, a beam of electrons moves back and forth across a cell’s surface, creating details of cell surface characteristics.
SEMs knock electrons off the specimen and these electrons come together to form an image.
SEM images can be three-dimensional.
Specimens do NOT have to be thin like when using a TEM.
Resolution is lower than that produced by a TEM.
