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2 Cytoskeleton

3 MICROTUBULES MICROFILAMENTS copyright cmassengale Microfilaments are threadlike & made of ACTIN Microtubules are tubelike & made of TUBULIN Cytoskeleton Dynamic system – constantly forming and disassembling Network of protein fibers found in all eukaryotic cells

Functions of Eukaryotic Cell Features StructureFunction(s) Cytoskeleton 1.Maintains cell shape ( 1.Maintains cell shape (Supports the shape of the cell 2.Anchors organelles and proteins( 2.Anchors organelles and proteins(Keeps organelles in fixed locations 3.Allows for organelle movement and cellular movement in some cell types

Endomembrane System Rough Endoplasmic Reticulum Smooth Endoplasmic Reticulum Vesicle Golgi Apparatus Vesicle Lysosome Vesicle PlasmaMembrane

6 Endoplasmic Reticulum - ER Connects to nuclear envelope & cell membrane Divides cell into compartments where different cellular functions occur Functions in Synthesis of cell products & Transport copyright cmassengale

Endomembrane System Series of membranes throughout the cytoplasm Network of hollow membrane tubules One of the fundamental distinctions between eukaryotes and prokaryotes 7 Two kinds of ER ---ROUGH & SMOOTH

copyright cmassengale8 Two kinds of ER ---ROUGH & SMOOTH Ratio of RER to SER depends on cell’s function

9 Rough Endoplasmic Reticulum (Rough ER) Has ribosomes on its surface, attachment of ribosomes to the membrane gives a rough appearance Synthesis of proteins to be secreted, sent to lysosomes or plasma membrane and proteins for EXPORT out of cell copyright cmassengale

10 Rough Endoplasmic Reticulum (Rough ER) Proteins are made by ribosomes on ER surface They are then threaded into the interior of the Rough ER to be modified and transported copyright cmassengale

Rough Endoplasmic Reticulum Synthesis and secreted of: proteins, integral membrane proteins carbohydrate chains phospholipids PROTEIN MODIFICATION starting point of BIOSYNTHETIC PATHWAY Functions:

12 Smooth Endoplasmic Reticulum Smooth ER lacks ribosomes on its surface Is attached to the ends of rough ER Makes cell products that are USED INSIDE the cell copyright cmassengale

nucleus endoplasmic reticulum smooth rough

14 Functions of the Smooth ER Variety of functions. Makes membrane lipids (steroids) Regulates calcium (muscle cells) Destroys toxic substances synthesis of steroid hormones detoxification of organic molecules glucose release from liver copyright cmassengale

Functions of Eukaryotic Cell Features StructureFunction(s) Rough Endoplasmic Reticulum (RER) 1.Associated ribosomes produce proteins 2.Prepares proteins for export Smooth Endoplasmic Reticulum (SER) 1.Lipid Synthesis 2.Drug detoxification 3.Transport of proteins from RER RER SER

Large subunit of ribosome Small subunit of ribosome Ribosome

17 Ribosomes Can be attached to Rough ER OR Be free unattached (in cytoplasm or associated with internal membranes) copyright cmassengale

Ribosomes Made of PROTEINS and r RNACell’s Found in all cell types 18

In the late 50’s, scientists began seriously considering the structure of the ribosome copyright cmassengale19 Ribosome - protein synthesizer consisting of two subunits Larger one &Smaller one

Prokaryote 70S Ribosome two subunits Larger one, “50S”,. Smaller is “30S”

50S and 30S??? Related to their respective sizes. Numbers actually measures of how quickly each subunit sinks to the bottom of a container of liquid when spun in a centrifuge One subunit smaller than other, but both are larger than average protein

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Structure and RNA Recently discovered - about two-thirds of ribosome’s mass made up of RNA Most important functions of ribosome performed by RNA. This has been found because of atomic knowledge of structures of 50S and 30S and their assemblage into 70S (One might logically think it to be 80S, but it really isn’t)

Ribosomes Figure 4.19 Ribosomes from eukaryotes are larger and constructed differently

PROKARYOTE VS. EUKARYOTE RIBOSOMES

Prokaryotes ribosome Vs eukaryotes ribosome's EukaryotesProkaryotes RateEcoli Composition60%protein & 40% ribonucleic acids S = sedimentation coefficient 80SS 70 small sub unit40S30S Large sub unit60S50 S اsmall sub unit rRNA 18 S16 S No of bases Large sub unit rRNA (28 S)+ (5S)(23 S)+ (5S) No of bases4800, , 120 Proteins in small sub unit(33,( S1, S2,S3(21,( S1, S2,S3 Proteins in large sub unit50(L1, L2,L3)31(L1, L2,L3)

copyright cmassengale27 FUNCTION

Small Ribosomal Subunit  The small ribosomal subunit is relatively flexible, assuming different conformations. E.g., the 30S subunit of a bacterial ribosome was found to undergo specific conformational changes when interacting with a translation initiation factor.

The overall shape of the 30S ribosomal subunit is largely determined by the rRNA. The rRNA mainly consists of double helices (stems) connected by single-stranded loops. The proteins generally have globular domains, as well as long extensions that interact with rRNA and may stabilize interactions between RNA helices. Small ribosomal subunit of a thermophilic

The 30S subunit FUNCTION 30S controls flow of information during protein synthesis 30S finds an mRNA and then makes sure that each t RNA is matched up correctly on mRNA It’s been suggested that mRNA enters through small hole in 30S (shown here in center of left side) mRNA then extends up into the place where translation occurs, located in cleft between top part, “head”, and bottom part, “body”

The 50S subunit The interior of the large subunit is mostly RNA. 50S made of two RNA strands: a long one, shown in an orangey color, and shorter one, shown in yellow Blue things in the picture are a few of many proteins that have bound to ribosome’s surface

Large ribosome subunit: Proteins are distributed mainly on the surface. Some proteins have long tails that extend into the interior of the ribosome and keep the RNA strands in place. These tails, which are highly basic, interact with the negatively charged RNA.

The 50S subunit This part of ribosome contains site where new peptide bonds are formed when proteins are synthesized mRNA would be located horizontally in groove across middle To help with protein synthesis, subunit uses adenine RNA nucleotide, shown by green dot in center

34 POLYPEPTIDE AND POLYSOME Poly-ribosomes consistes of a group of ribosomes (4-5) formed in nucleus and moved to cytoplasm

ASSIGMENT COMPERE BETWEEN RER AND SER EUKARYOTIC AND PROKARYOTIC RIBOSOME copyright cmassengale35

copyright cmassengale36 That is the end