2.6 Prokaryotic And Eukaryotic Cells (2.1.1) Flashcards
1
Q
Prokaryotes can be classed into two evolutionary domains. What are these?
A
Archaea and Bacteria
2
Q
When did prokaryotic cells first appear?
A
3.5 billion years ago
3
Q
Scientists believe that these early cells were adapted to living in extremes of ________, ___, and ____________.
A
salinity, pH, temperature
4
Q
What are extremophiles? (3)
A
- Extremophiles are organisms that can survive in environments that are too extreme for most other life forms, such as places with extreme temperatures, pressure, radiation, salinity, or pH levels.
- They can be found in hydrothermal vents and salt lates - similar environments to those believed to have made up the early Earth.
- They are usually of the domain Archaea and more recently they have been found in more hospital environments such as soil and the human digestive system.
5
Q
Prokaryotic cells are similar to eukaryotic cells in that they have: (4)
A
- A plasma membrane
- Cytoplasm
- Ribosomes for assembling amino acids into proteins
- DNA and RNA
6
Q
Prokaryotic cells are different from eukaryotic cells as they: (7)
A
- Are much smaller
- Have a much less well-developed cytoskeleton with no centrioles
- Do not have a nucleus
- Do not have membrane-bound organelles such as mitochondria, endoplasmic reticulum, chloroplasts or Golgi apparatus
- Have a wall made of peptidoglycan and not cellulose
- Have smaller ribosomes
- Have naked DNA that is wound around histone proteins but floats free in the cytoplasm, as a loop (not linear chromosomes)
7
Q
What 4 things do only some prokaryotic cells have?
A
- A protective waxy capsule surrounding their cell wall
- Small loops of DNA, called plasmids, as well as the main large loop of DNA
- Flagella: long whip-like projections that enable them to move. The structure of these flagella differs from that of eukaryotic undulipodia
- Pili: smaller hair-like projections that enable the bacteria to adhere to host cells or to each other, and allow the passage of plasmid DNA from one cell to another
8
Q
Describe how the structure of the DNA in prokaryotes is different from the DNA in eukaryotes (4)
A
- The DNA in eukaryotic cells is present within a nucleus and exists as multiple chromosomes, which are supercoiled, and each one wraps around a number of proteins called histones, forming a complex for efficient packaging. This complex is called chromatin and chromatin coils and condenses to form chromosomes. Eukaryotic genes are generally switched on and off individually.
- Prokaryotes generally only have one molecule of DNA, a chromosome, which is supercoiled to make it more compact. This is called naked DNA and it is not wound around histone proteins but floats free in the cytoplasm, as a loop (not linear chromosomes).
- The genes on the chromosome are often grouped into operons, meaning a number of genes are switched on or off at the same time.
- Also, some prokaryotic cells have additional small loops of DNA, called plasmids, as well as the main large loop of DNA.
9
Q
Describe how the structure of ribosomes in prokaryotes is different from ribosomes in eukaryotes (2)
A
- The ribosomes in prokaryotic cells are smaller than those in eukaryotic cells. Their relative size is determined by the rate at which they settle, or form a sediment, in solution. The larger eukaryotic ribosomes are designated 80S and the smaller prokaryotic ribosomes, 70S.
- They are both necessary for protein synthesis, although the larger 80S ribosomes are involved in the formation of more complex proteins.
10
Q
Describe how the structure of the cell wall in prokaryotes is different from the cell wall in eukaryotes (2)
A
- Prokaryotic cells have a cell wall made from peptidoglycan, also known as murein. It is a complex polymer formed from amino acids and sugars.
- However, eukaryotic cells have a cell wall made from cellulose, a carbohydrate polymer, or chitin.
11
Q
Describe how the structure of the flagella in prokaryotes is different from the flagella in eukaryotes (2)
A
- The flagella of prokaryotes is thinner than the equivalent structure of eukaryotes and does not have the 9 + 2 arrangement.
- The energy to rotate the filament that forms the flagellum is supplied from the process of chemiosmosis, not from ATP as in eukaryotic cells.
12
Q
Describe how the flagellum is attached to prokaryotic cells and how it is moved (3)
A
- The flagellum is attached to the cell membrane of a bacterium by a basal body and rotated by a molecular motor.
- The basal body attaches the filament comprising the flagellum to the cell-surface membrane of a bacterium.
- A molecular motor causes the hook to rotate giving the filament a whip like movement, which propels the cell.
13
Q
Describe the theory of endosymbiosis
A
- The theory of endosymbiosis is that mitochondria and chloroplasts, and possibly other eukaryotic organelles, were formerly free-living bacteria, that is, prokaryotes. The theory is that these prokaryotes were taken inside another cell as an endosymbiont - an organism that lives within the body or cells of another organism when some prokaryote cells with infolded membranes (for making ATP, or containing chlorophyll) invaded, or were engulfed by, some other prokaryotes, but not digested.
- As the invaded prokaryote’s plasma membrane folded inwards around the invading cell, this produced the double membrane of what are now chloroplasts and mitochondria. Both chloroplasts and mitochondria share characteristics with prokaryotic cells. They: have small ribosomes, have loops of DNA, also contain RNA, and can divide by binary fission.
14
Q
What is the evidence supporting the endosymbiont theory? (4)
A
- DNA: both mitochondria and chloroplasts have their own circular DNA, which is separate from the DNA in the cell nucleus. The DNA in chloroplasts is similar to that of photosynthetic bacteria, while mitochondrial DNA is similar to that of aerobic bacteria.
- Reproduction: both mitochondria and chloroplasts replicate by binary fission, similar to some prokaryotic cells.
- Ribosomes: both mitochondria and chloroplasts have 70S ribosomes, which are the same as those found in prokaryotic cells.
- Size: both mitochondria and chloroplasts are about the same size as prokaryotic cells.
15
Q
What is the cell wall of fungi cells made of?
A
Chitin
