Cell Structure

Cell StructureObjectivesMUST: Draw diagrams of a prokaryotic cell and a eukaryotic cell SHOULD: Describe the functions of cell organelles

COULD: Distinguish between prokaryotes and eukaryotes

2Prokaryotic Vs. EukaryoticCells are divided into groups based on major characteristics. One particular grouping that we look at is the separation of cells into 2 groups:

Prokaryotic (before nucleus)

Eukaryotic (true nucleus)

Prokaryotes are typically thought of as been less developed/less complex than eukaryotes.

Prokaryotes are much smaller in size (normally 1 10 m compared with 5-100 m for eukaryotes).

It is thought that prokaryotic cells existed prior to eukaryotic cells.

Prokaryotic cells occur in bacteria whereas eukaryotic cells are found in animals, plants, protozoa and fungi.

Prokaryotic Vs. EukaryoticBe able to draw, label and state the function of each part of the cell Prokaryotic Cell E.Coli

Be able to draw, label and state the function of each part of the cell Eukaryotic Cell

TaskMake a copy of both cells in your copy book.They should be at least a page in size.Annotate the diagram with the FUNCTIONS of each of the organelles.

You have 15minutes to complete.

You will have a mini-test of the functions next lesson. TASKSwap books and according to the Mark Scheme provided give your partner a mark out of 9.

Be careful not to ruin their work so write small and in pencil! Mark Scheme Prokaryotic CellAward [1] for each structure clearly drawn and correctly labelled.Cell wall; (with some thickness)Plasma membrane; (shown as single line or very thin)Cytoplasm;Pilus/pili; (shown as single lines)Fagellum/flagella; (shown as thicker and longer structures than piliand embedded in cell wall)70S ribosomes;Nucleoid / naked DNA;Approximate width 0.5 m / approximate length 2.0 m dimensions shown.Correct shape - rounded-corner rectangle with length at least twice its width.

Deduct 1 mark for each eukaryotic structures included.Mark Scheme Eukaryotic CellAward [1] for each structure clearly drawn and correctly labelled.Plasma membranesingle line surrounding cytoplasm;Nucleus with a double membrane and pore(s) shown;CytoplasmMitochondria(ion) with a double membrane, the inner one folded into internal projections, shown no larger than half the nucleus;Rough endoplasmic reticulummulti-folded membrane with dots/small circles on surface;Golgi apparatusshown as a series of enclosed sacs with evidenceof vesicle formation;Ribosomes dots/small circles in cytoplasm/ribosomes on rER;Lysosome;Approximate diameter of 10.0m dimensions shown.Deduct 1 mark each for any plant cell structures shown.

The nucleus is the largest cell organelle.

It is surrounded by two membranes known as the nuclear envelope.

The outer of these two membranes is continuous with the endoplasmic reticulum.

The nuclear envelope is separated by nuclear pores which allow exchange of materials between the nucleus and the cytoplasm.

Nucleus and Nucleolus Within the nucleus the chromosomes are found in a loosely coiled state known as chromatin. Chromosomes contain DNA, which is organised into genes and which controls the activities of the cell.

The nucleolus manufactures ribosomes using the information in its own DNA.

Nucleus and Nucleolus

Nucleus and Nucleolus Plasma Membrane Controls substances that enter and leave the cell. It is made up of a double layer of water repellent molecules.

We will look more closely at the plasma membrane later on.

Mitochondria Site of aerobic respiration.

They are surrounded by two membranes, the inner of which is the cristae which goes into the interior called the matrix. As a result of carrying out respiration, mitochondria makes ATP, which is the universal energy carrier in cells.

RibosomesRibosomes are tiny organelles which may be found roaming free in the cytoplasm or attached to the endoplasmic reticulum.

Ribosomes are the site of protein synthesis.

They are made of RNA (ribonucleic acid) and protein.

Ribosomes attached to Rough Endoplasmic Reticulum (rER) produce proteins for secretion outside of the cell.

Free ribosomes produce proteins for use internally within the cell.

Ribosomes

Endoplasmic ReticulumAre an extensive system of membranes running through the cytoplasm.

Attached to the surface of many of these membranes are ribosomes.

The areas of endoplasmic reticulum that have ribosomes attached are known as rough endoplasmic reticulum (rER), whereas the fewer sections which do not have ribosomes present are called smooth endoplasmic reticulum (sER).

The two different types of ER are known to have different functions.

The rough ER transports the proteins which are manufactured in the ribosomes around the cell.

Endoplasmic Reticulum

Golgi ApparatusThe Golgi apparatus is a stack of flattened sacs (cisternae).

The stack is constantly been formed at one end from vesicles which bud off from the ER and broken down at the other end to form Golgi vesicles.

The apparatus collects, processes and sorts molecules (in particularly proteins), ready for transport in the Golgi vesicles either to other parts of the cell or out of the cell.

LysosomesGolgi vesicles are also used to make lysosomes

Proteins for secretion are modified

Possible addition of carbohydrate or lipid components to protein

Packaged into vesicles for secretion

LysosomeAre spherical sacs, surround by a single membrane and have no internal structure.

They contain hydrolytic enzymes which must be kept separate from the rest of the cell to prevent damage. Lysosomes are responsible for the breakdown of unwanted structures such as old organelles.

In white blood cells they will be responsible for the breakdown of pathogens. Prokaryotic Cell

Differences ProkaryoticEukaryoticUse your drawings to try and find differences between Eukaryotic and Prokaryotic cells. (Remember: Plant cells are Eukaryotic too).ProkaryoticEukaryoticnaked DNAprotein associated with DNA;DNA in cytoplasm /no nucleusDNA in nucleus / nucleus present;circular DNAlinear chromosomes/DNA molecules;no mitochondriamitochondria;70S ribosomes present (Svedberg)80S ribosomes present;no membrane bound organellesMembranes bound organelles;pili presentpili absent;plasmids (sometimes) presentplasmids absent;cell wall presentcell wall only present in plants/fungi;Do not accept cell wall sometimes present.flagella solidflagella flexibleFrom the SyllabusUnderstandings Prokaryotes have a simple cell structure without compartmentalization. Eukaryotes have a compartmentalized cell structure.

Applications and skills Application: Structure and function of organelles within exocrine gland cells of the pancreas and within palisade mesophyll cells of the leaf. Application: Prokaryotes divide by binary fission. Skill: Drawing of the ultrastructure of prokaryotic cells based on electron micrographs. Skill: Drawing of the ultrastructure of eukaryotic cells based on electron micrographs.