Cells and organelles Flashcards
The size of cells
Cells are approximately 1/100th mm (a tenth of a human hair thickness)
Properties of cells
Cells are microscopic that acts as independent units.
Cells can grow and reproduce (divide).
Cells have a finite lifetime as they can die due disease, design or age.
Cells have internal process that allow them to change, adapt and respond .
Plasma membrane
a semi-permeable membrane that is composed of bilayer of lipid molecules and proteins.
Membrane structure
The fluid mosaic model illustrates that the membrane has two layers of lipids (hydrophilic heads on the outside and hydrophobic tails on the inside) and proteins.
Prokayotic cells
Cells with no internal membranes and only have enclosing membranes. The DNA is packaged but not enclosed by the membrane. Relatively very small to eukaryotic cells. They are few thousandth of a mm in size.
Eukaryotes
They have internal membranes and organelles. The cytoplasm is divided by the membrane to enclose compartments or organelles.
Pathway of protein expression
DNA (genes) -> transcription -> mRNA -> translation -> protein
Nuclear Envelope
A double membrane in which DNA is packaged and enclosed in.
Nuclear pores
mRNA passes from the nucleoplasm to the cytoplasm through the nuclear pores. They are selectively aqueous channels.
DNA packaging
DNA is packaged with histones which forma a complex called chromatin
Chromatin packaging
Chromatin are packed as either euchromatin (active) or heterochromatin (inactive)
Ribosomes
Specialised organelles which produce proteins by decoding the mRNA strand and covert it into linear polypeptides (proteins).
Nucleolus
assembles newly made ribosomes at amplified ribosome genes
Signal sequence
A short sequence of amino acids and any proteins with the signal sequence are recognised and ribosomes become bound to the rough endoplasmic reticulum.
Free ribosomes
Many ribosomes remain free during protein translation and they synthesise proteins that are bound for the cytosol, membrane or nucleus.
