BTEC Applied Science Unit 1 Biology Prokaryotes, prokaryotic cells. Now cells, you've got eukaryotic cells and prokaryotic cells. Eukaryotic cells are plant and animal cells.
Prokaryotic cells, now single cell organisms with no membrane, no membrane bound organelles, for example bacteria. Think of them as bacteria. A very simple definition is that prokaryotic cells don't have a nucleus, whereas eukaryotic cells do.
So eukaryotic cells, plants and animals, prokaryotic cells, mostly bacteria. The bits you need to know, lots of lists of things you need to know in biology, these are all the different bits of a prokaryotic cell. and we'll work our way through them.
I'll tell you what they are. The nucleoid. So not a nucleus, but a nucleoid. A single circular length of DNA folded up inside the cell. That's the nucleoid.
Not bound by a membrane, not inside a membrane. Ribosomes. The ribosomes are floating around. They're not attached to any reticulum. 70S ribosomes, which are smaller and less active than the 80S ones.
So 70S simpler ribosomes floating around in the cytoplasm. The slime capsule, which is the outer layer outside the cell wall, and this prevents the cell from drying out, helps to protect from white blood cells, helps to stick to surfaces. the slime layer, the slimy things, these prokaryotic cells. The cell wall, made of long chained molecules, made of a sugar and amino acids called peptoglycan.
I'm going to talk more about that in a bit. Peptoglycan. The cell wall supports and protects and keeps its shape just as in a plant cell, what it does in a plant cell. plasmids, double-stranded DNA in a circular structure, these little circles of DNA are called plasmids, additional genes that aid in survival, for example antibiotic resistance and producing toxins.
Now, peptidoglycan, I'm going to talk a bit more about this stuff. Remember it's what the cell wall is made of. What bacterial cell walls are made from, made of long chain molecules which are made of sugars and amino acids.
Now, the walls can be thick or thin depending on the type of bacteria. In something called a gram test, we're going to talk about a gram test, they absorb the stain. Now, what's a gram test?
I'm not going to go through all the details of a gram test and you won't be asked them in the exam but we can say that there are two types of bacteria. They are gram positive and gram negative. Now the gram positive ones you can stain them. They don't have an outer membrane and they have a thick peptidoglycan cell wall which absorbs the stain.
Basically, you put some staining stuff on them and do they change colour? And the gram-positive ones do. And they do because they don't have an outer membrane and there's lots of a thick wall of peptoglycan to absorb the stain. The gram-negative ones, they have an outer membrane and the cell wall is thin so they don't keep the stain. They don't become stained.
So gram-positive and gram-negative. Now, so what? Well, here we see a diagram showing gram-positive and gram-negative. Notice that the gram-positive ones have a thick cell wall, which goes purple.
The gram-negative ones have an outer membrane and a thin cell wall. Now, gram-negative bacteria are more resistant to antibiotics, as they have more protection, because it's harder for them. antibiotics to get in.
So gram-negative bacteria are more resistant to antibiotics. Here's a little exercise for you to do. Can you fill in all the labels?
One thing I didn't mention were the little taily things on the end which spin around and help the bacterium swim around, although it was on a label on one of the diagrams. What are bacterial cell walls made from? Starts with P. Why are some bacteria gram-positive and others gram-negative?
What are the differences in structure between the two? And why is it useful for a doctor to know the difference?