AS BIOLOGY The ultrastructure of the cell LEARNING OBJECTIVES By the end of this section you should be able to:- Recognise the following organelles from a diagram of the eukaryotic animal and plant cell (rough and smooth endoplasmic reticulum, Golgi apparatus, mitochondria, ribosomes, lysosomes, chloroplasts, plasma (cell surface) membrane, nuclear envelope, centrioles, nucleus, nucleolus and cilia). Outline the functions of the following structures:- rough and smooth endoplasmic reticulum, Golgi apparatus, mitochondria, ribosomes, lysosomes, chloroplasts, plasma (cell surface) membrane, nuclear envelope, centrioles, nucleus, nucleolus and cilia.

The Eukaryotic Cell The Beginnings Robert Hooke was the first person to observe cells in He looked at thin slices of cork under a very simple microscope. The cork appeared as little boxes which he called cells. In 1883 MathiasSchleiden and Theodor Schwann proposed that all plants and animals were composed of cells which were the basic building blocks of life. In 1855 Rudolf Virchow stated that new cells arise from the division of pre-existing cells and that chemical reactions needed for life occurred inside the cell. All this work led to the formation of the cell theory (click to complete exercise on cell theory)cell theory For more information click on link below

Eukaryotic Animal Cell Eukaryotic means “true nucleus” Eukaryotic cells have a nucleus which contains the DNA. Eukaryotic animal cells are surrounded by a cell membrane. Inside is the jelly like substance called cytoplasm. Contained in the cytoplasm is the nucleus and other organelles (copy the glossary file into your area and continue to add words and meanings) organelles The other cell organelles include the endoplasmic reticulum,(rough & smooth) mitochondria, Golgi apparatus, ribosomes, lysosomes, centrioles, cilia, nucleolus.

Endoplasmic Reticulum STRUCTURE Complex system of sheet like double membranes continuous with the nuclear membrane Fluid filled spaces/sacs between the membranes called CISTERNAE which allow materials to be transported through cell Two types of ER – –smooth – has no ribosomes attached (RER) –rough – has ribosomes attached (SER) FUNCTION Forms an extensive transport system Site of protein synthesis (Rough ER) Site of lipid, steroid and carbohydrate synthesis (smooth ER) Stores and transports these materials SEE DIAGRAM

Mitochondria STRUCTURE Relatively large organelle Rod/sausage shaped – 1um – 5um Have a double membrane –The outer controls the entry & exit of materials –Inner has many folds called cristae Surface of each crista is covered with stalked particles where ATP is made Mitochondria are filled with a jelly like matrix The matrix contains proteins, lipids, ribosomes and loops of DNA Mitochondria can replicate themselves when the cell divides FUNCTION Site of aerobic respiration (Krebs cycle & oxidative phosphorylation) Responsible for the production of energy rich ATP molecules The numbers of mitochondria reflect the metabolic activity of the cell – so large numbers are found in muscle and liver cells SEE DIAGRAM

Golgi apparatus STRUCTURE Formed from small pieces of rough ER which form small vesicles which join to make a Golgi body Chemicals made in the ER collect in the Golgi body where they are modified Small vesicles can then be ‘pinched’ off the Golgi body carrying new chemicals away which are secreted when the vesicle reaches the cell membrane Some of the vesicles become lysosomes FUNCTION Assembling glycoproteins (such as mucin) by combining carbohydrate and protein Transporting and storing lipids Formation of lysosomes Producing digestive enzymes Secretes carbohydrates which are used in the formation of plant cell walls and in insect cuticles SEE DIAGRAM What have you learnt? Click here to walk the plank

Ribosomes STRUCTURE Small dense structures found in huge numbers. Can be attached to the rough ER of floating in the cytoplasm. Are about 20 – 25 nm in diameter in eukaryotic cells and slightly smaller in prokaryotic cells (80s type – prokaryotic) (70s type – eukaryotic) Made up from two sub units FUNCTION Synthesize proteins Synthesize enzymes SEE DIAGRAM

Lysosomes STRUCTURE Small vacuoles formed when small pieces of Golgi body are pinched off Contain hydrolytic enzymes which digest materials in the cell SEE DIAGRAM FUNCTION Release enzymes which destroy worn out organelles Digest material taken into the cell (eg white blood cells which have engulfed a bacterium) – phagocytosis Release enzymes to the outside of the cell which digest material around the cell – exocytosis Completely break down cells after they have died – autolysis

Plasma (cell surface) membrane STRUCTURE This is the boundary between the cell cytoplasm & the environment Is partially permeable Made up 45% protein & 45% phospholipids with the remaining 10% cholesterol, glycoprotein & glyolipids FUNCTION Controls movement of substances in & out of the cell Forms a recognition site so that the body’s immune system can recognize its own cells Acts as a receptor site for the attachment of specific hormones and neurotransmitters. SEE DIAGRAM

Nucleus, Nucleolus & Nuclear envelope STRUCTURE Largest organelle in the cell (10um diameter) Surrounded by a nuclear membrane / envelope Double membrane – outer is continuous with the ER Nuclear pores in the membrane allow the passage of large molecules in & out (eg messengerRNA) Material inside the nucleus is called nucleoplasm – this contains chromatin which makes up the DNA of the cell – in non-dividing cells it is spread out and during cell division it condenses to form the chromosomes A spherical structure called the nucleolus is found in the nucleus – this makes ribosomal RNA and assembles the ribosomes. FUNCTION Acts as the control centre of the cell through the production of mRNA and protein synthesis Retains the genetic material in the cell in the form of DNA / chromosomes Manufactures ribosomal RNA (rRNA) & ribosomes Starts the process of cell division SEE DIAGRAM What have you learnt? Click here to complete the crosswordClick here to complete the crossword

Cilia STRUCTURE 3-10 um in length, 0.2um in diameter Made of rings of 9 pairs of microtubules Have basal body embedded in cytoplasm Rest extends from basal body Only a few types of cell possess cilia On cells which have cilia there are large numbers FUNCTION To move an entire organism (eg in paramecium it propels it through the water) To move material within an organism ( eg cilia in the lining of the respiratory tract) SEE DIAGRAM

CENTRIOLES (not found in plant cells) Two short bundles of hollow cylinders (microtubules) positioned at right angles to each other Found just outside the nucleus in a clear area of cytoplasm called the centrosome Wall of each centriole is made of 9 triplets of tubes arranged at an angle During cell division they migrate to opposite poles to produce the spindle – which helps to move the chromosomes during cell division SEE DIAGRAM

Chloroplasts Found inside photosynthetic tissues of plants (abundant in palisade mesophyll cells of leaves) Flat discs 2-10 um in diameter & 1um thick Have a double membrane called the chloroplast envelope Inner membrane folded into a series of lamellae Membrane controls the entry & exit of substances Inside the membrane is a fluid – stroma – which contains the enzymes involved in photostnthesis Small amounts of DNA and oil are found in the stroma In stroma is a network of flattened sacs called thylakoids Grana (granum = sing) are formed when many thylakoids are stacked together (like a pile of coins) (thylakoids also called lamella) Chlorophyll molecules are attached to the thylakoids Large starch grains are also present which act as a tempory store of charbohydrate made in photosynthesis SEE DIAGRAM Click here to label the eukaryotic animal cell

Click hereClick here to play cell organelles catch phrase