Today’s blog will explain cell structure under OCR A Level Biology. Many students find it difficult to understand the cell structure and microscopy. So, if you are among them, you can receive guidance from A Level Biology Tutor at Bright Mind Tutors. We have years of experience and helped many students clear their exams. You can book a free trial with our tutors to learn about our teaching style.
OCR Biology A Level: The Ultrastructure of Eukaryotic Cells
All living organisms are classified into two distinct domains: eukaryotes and prokaryotes. Eukaryotic organisms have cells that contain a nucleus, whereas prokaryotic organisms lack a nucleus and other membrane-bound organelles. Eukaryotic cells, such as those found in animals, plants, and fungi, may include the following organelles:
- Nucleus
- Nucleolus
- Nuclear envelope
- Rough endoplasmic reticulum (RER)
- Smooth endoplasmic reticulum (SER)
- Golgi apparatus
- Ribosomes
- Mitochondria
- Lysosomes
- Chloroplasts
- Plasma membrane
- Centrioles
- Cell wall
- Flagella
- Cilia
- Vacuole
Cell structure comes under OCR A Level Biology specification. So, you must learn about it to get in-depth information about the cell structure.
Protein Production
- Translation of mRNA into a polypeptide chain occurs on ribosomes, which can be free in the cytoplasm or attached to the rough ER.
- The long polypeptide chain is folded at the rough ER and then transported to the Golgi apparatus in vesicles.
- Various enzymes modify and process the polypeptides at the Golgi apparatus. Modifications may include the addition of a carbohydrate chain or the attachment of a sulfate or phosphate group.
- The modified protein is then packaged into another vesicle, which transports it to the specific part of the cell where it is needed. If the protein is a carrier protein, the vesicle will deliver it to the plasma membrane for incorporation.
Cytoskeleton
The cytoskeleton, a network of protein threads in the cytoplasm, consists of microfilaments and microtubules in eukaryotes. It supports and positions the cell’s organelles, facilitates the movement of organelles and chromosomes during cell division, strengthens the cell, maintains its shape, and enables the movement of cilia and flagella. Moreover, you can learn from OCR A Level Biology Past Papers to revise for your exams.
Learn the Difference between Eukaryotic and Prokaryotic Cells from A Level Biology Tutor
Prokaryotes lack membrane-bound organelles, so they don’t have mitochondria, Golgi apparatus, endoplasmic reticulum, or a nucleus. Their DNA is a single circular chromosome that floats freely in the cytoplasm, along with extra DNA in small circular plasmids. Prokaryotes have smaller ribosomes (70S) compared to eukaryotes (80S).
In eukaryotes like plants and fungi, cell walls are made of cellulose and chitin, while bacterial cell walls consist of murein. Prokaryotic cells are significantly smaller than eukaryotic cells. Both can have flagella, but in prokaryotes, flagella are made of flagellin, whereas in eukaryotes, they are composed of microtubules.
Microscopy
A light microscope uses light to magnify objects up to 1,500x, with a resolution of about 0.2 μm, making it unsuitable for viewing smaller organelles like ribosomes and lysosomes. It is ideal for observing whole cells or tissues and can visualize living cells, allowing real-time observation of processes like cell division.
Laser scanning confocal microscopes are a specialized type of light microscope. They use laser beams to scan specimens labelled with fluorescent tags, producing clearer 3D images and allowing views at different depths.
Transmission electron microscopes (TEM) have a much higher resolution (around 0.0002 μm) than light microscopes, allowing visualization of individual organelles. TEMs use electrons instead of light but require fixed, non-living samples placed in a vacuum.
Scanning electron microscopes (SEM) offer lower resolution (around 0.002 μm) than TEMs but can produce 3D images of cells and organelles. Like TEMs, SEMs cannot be used with live cells. Both TEMs and SEMs are large, expensive, and typically found in specialized research facilities and hospitals.
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