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Transcript
Lesson 2 • Recognise structures as seen under the electron microscope, e.g. nucleus, nucleolus, nuclear envelope, rough and smooth endoplasmic reticulum, Golgi apparatus, ribosomes, mitochondria, lysosomes and chloroplasts. • Outline the functions of these structures. The detail of the inside of cell is called the cell’s ultrastructure. • Usually only one nucleus per cell • Regulates all cell activity • Contains the DNA which carries the information for protein synthesis • The DNA is associated with histone protein to form chromatin • Surrounded by a nuclear envelope (double layer membrane) which has nuclear pores • Nucleus is continuous with endoplasmic reticulum Nucleus • Found inside the nucleus • Makes RNA and ribosomes which pass into cytoplasm. • Usually stains darker than the rest of the nucleus on EM Nucleolus Rough and smooth endoplasmic reticulum • Rough ER – with ribosomes – Protein synthesis • Smooth ER – without ribosomes – Synthesis of steroids and lipids • Intracellular membrane system – substances are transported in the spaces Golgi Apparatus • Stack of flattened sacs (cisternae), each separated from the cytoplasm by a membrane • Modifies and packages cell products (proteins from rER) • Encloses substances in vesicles to be secreted • Involved in production and secretion of many proteins, carbohydrates and glycoproteins • Vesicles containing digestive enzymes (hydrolytic enzymes) to break down materials • Surrounded by a single membrane. • White blood cell lysosomes break down microorganisms. • Lysosome (acrosome) in sperm cell helps to penetrate egg Lysosomes • Site of aerobic respiration – where ATP (adenosine triphosphate) is produced • 2 membranes separated by fluid filled space • Internal membrane folded into cristae • Lots of mitochondria found in active cells – skeletal muscle (physically active), hepatocytes (metabolically active) Mitochondria (2-5 µm long) • • • • • Chloroplasts Only found in plant cells – site of photosynthesis. 2 membranes separated by fluid filled space Inner membrane – flattened sacs called thylakoids. A stack of thylakoids is called a granum. Inside – stroma which is also involved in photosynthesis Chlorophyll molecules found on thylakoid membranes. (4-10 µm long) Ribosomes • Lots of ribosomes in a cell (50 000 or more) • Found on rough ER and also as free ribosomes in the cytoplasm • Site of protein synthesis (where mRNA and tRNA meet so the protein is assembled). Centrioles • Two short cylinders of microtubules • Pair found next to nucleus in animal cells • Aid cell division – move to opposite poles (ends) of the cell as spindle develops