Lecture 4: Introduction to human cells Flashcards
Classification of cells
Prokaryotes-
Single celled organisms without a nucleus.
Examples include eubacteria (true bacteria), archaebacteria (“extremophiles”), cyanobacteria.
Eukaryotes-
Single or multicellular organisms with a membrane bound nucleus.
Includes all plants and animals – yeasts, moulds, humans.
The variety of human cells
All cells have same genetic code.
All cells have similar internal structures but vastly different functions.
cytosol
Everything within cell except for nucleus and organelles
cytoplasm
Everything within cell except for nucleus
Central dogma of cell biology
The ‘Central Dogma’ is the process by which the instructions in DNA are converted into a functional product.
DNA- transcription- RNA - translation- proteins
Nucleus
Primary function is the storage and transmission of genetic information to the next generation of cells.
Genetic information is coded in molecules of DNA, is also used to synthesize the proteins.
DNA, in association with proteins, forms a fine network of threads known as chromatin.
During cell division, chromatin threads become condensed, forming chromosomes.
Nuclear envelope
Composed of two membranes.
At regular intervals along the surface of the nuclear envelope there are circular openings known as nuclear pores.
DNA is transcribed to make RNA molecules that move out of the nucleus through these nuclear pores (transcription).
Proteins that modulate the expression of various genes in DNA move into the nucleus through these pores.
Endoplasmic reticulum (ER)
Two forms of endoplasmic reticulum can be distinguished: rough (granular) and smooth (agranular).
Rough ER has ribosomes bound to its cytosolic surface, and it has a flattened-sac appearance. Rough ER is involved in packaging proteins to send to the Golgi apparatus.
Smooth ER has no ribosomal particles on its surface and has a branched, tubular structure. It is the site at which certain lipid molecules are synthesized, it plays a role in detoxification of certain hydrophobic molecules, and stores and releases calcium ions involved in controlling various cell activities.
Ribosomes
Protein factories of a cell located in the cytoplasm.
Protein molecules are synthesized from amino acids using genetic information carried by mRNA molecules from DNA in the nucleus (translation).
Proteins are synthesized
on free ribosomes and are released into the cytosol.
by ribosomes attached to the rough endoplasmic reticulum pass into the lumen of the reticulum.
Golgi apparatus
A series of closely apposed, flattened membranous sacs.
Proteins arriving at the Golgi apparatus from the rough ER undergo a series of modifications as they pass from one Golgi compartment to the next.
The Golgi apparatus sorts the modified proteins into discrete classes of transport vesicles that will travel to various cell locations – “address labels”.
Vesicles containing proteins to be secreted from the cell are known as secretory vesicles.
Mitochondria
Mitochondria participate in the chemical processes that transfer energy from the chemical bonds of nutrient molecules to newly created ATP molecules.
Lysosomes
Spherical organelles surrounded by a single membrane.
The fluid within a lysosome is acidic and contains a variety of digestive enzymes.
Peroxisomes
Peroxisomes are moderately dense oval bodies enclosed by a single membrane.
Peroxisomes consume molecular oxygen and performs reactions that remove hydrogen from organic molecules including lipids, alcohol, and potentially toxic ingested substances.
H2O2 detoxification
Endosomes/ Vesicles
Vesicles pinch off the plasma membrane travel to and fuse with endosomes.
The endosome can pinch off vesicles that then move to other cell organelles or return to the plasma membrane.
Endosomes are involved in sorting, modifying, and directing vesicular traffic.
