Cell Ultrastructure Plant and animal cells

Objectives  describe and interpret drawings and photographs of eukaryotic cells as seen under an electron microscope and be able to recognise the following structures: nucleus, nucleolus, nuclear envelope, rough and smooth endoplasmic reticulum(ER), Golgi apparatus, ribosomes, mitochondria, lysosomes, chloroplasts, plasma (cell surface) membrane, centrioles, flagella and cilia;  outline the functions of the structures listed  outline the interrelationship between the organelles involved in the production and secretion of proteins.

Cell Ultrastructure  The electron microscope has helped to reveal that plant and animal cells are much more than just sacs of gel.  Cells contain a range of organelles – each with its own function (division of labour) situated in a gel called the cytosol

Animal Cell

Plant Cell

The Nucleus  The largest cell organelle, visible even with the light microscope.  Made of 50% protein, 20% DNA and 30% RNA  The nucleus contains chromosomes (made of DNA and histone protein) which, in a non-dividing, cell appear as granules called chromatin

The Nucleus  The nucleus is surrounded by a double layer of membrane, forming a nuclear envelope and perforated by pores.

The Nucleus  The function of the nucleus is to contain inherited information and use that information to control cell activities.  The dark spot is the nucleolus which is made of RNA and makes ribosomes

Nucleus and Endoplasmic Reticulum

Endoplasmic Reticulum  This is a network of folded membranes and tubes continuous with the nuclear envelope, and found throughout the cytoplasm  Two types -Rough ER has ribosomes on the surface and is involved in the transport of proteins through the cell  Smooth ER is the site of lipid and steroid synthesis

Endoplasmic Reticulum

Ribosomes  Tiny organelles (about 20nm)  Positioned free in cytoplasm, in clusters or on the rough endoplasmic reticulum  Function to assemble polypeptides (protein chains) using coded information on RNA

Golgi Apparatus

 Also known as the Golgi body, this is a stack of flattened sacks  Its function is the refining and packaging of the proteins and lipids made in the ER into vesicles  Some carbohydrates are synthesised in the Golgi

Golgi apparatus

Golgi Apparatus  Substances produced in the cell are packaged into vesicles.  Some vesicles remain inside the cell, for example lysosomes  Lysosomes contain hydrolytic enzymes and are used for digesting worn out and damaged cell parts or, in the case of phagocytes, bacteria which have been engulfed  Other vesicles secrete their contents out of the cell in a process called exocytosis.

Mitochondria

 These have a double layer of membrane, the inner layer is folded into cristae.  Mitochondria are the site of cell respiration. They use oxygen to release energy from glucose  The energy is used to make a short term energy storage molecule called ATP

Mitochondria  The ATP molecules leave the mitochondrion and are used to fuel cell chemical reactions like protein synthesis.  Mitochondria contain a gel like matrix in which ribosomes and DNA are found

Chloroplasts

 At first site these look similar to mitochondria but the are bigger, green with chlorophyll and only found in plant cells.  Surrounded by a double layer of membrane they contain membranes in stacks called grana surrounded by a gel called the stroma  Their function is to absorb light energy and use it to combine water and carbon dioxide to make glucose, a process called photosynthesis

Photomicrograph of chloroplasts

Cytoskeleton  A network of protein fibres that provide an internal framework  Some fibres are microtubules – found within cells and in cilia and flagella on the surface of the cells  These move cell contents like vesicles or chromosomes during cell division

Cilia and Flagella  Structurally the same.  Cilia shorter, flagella (unipodia) longer.  Central pair of microtubules surrounded by nine pairs.  Function to move fluids across the cell surface or to move the cell  Different structure in bacteria

Plasma membrane  Both the cell surface membrane and the internal membranes are made of two layers of phospholipid molecules. This appears under the electron microscope as two dark lines separated by a pale band

The End