Chapter 3 Part 2! Pages (10 th and 11 th eds.)! The Cellular Level of Organization! Cellular Organelles and Protein Synthesis!

Transcription

1 Chapter 3 Part 2! Pages (10 th and 11 th eds.)! The Cellular Level of Organization! Cellular Organelles and Protein Synthesis! The Cell Theory! Living organisms are composed of one or more cells.! Cells arise from the division of preexisting cells.! Cells are the smallest units that perform all vital physiological functions.! Each cell maintains homeostasis at the cellular level.! Organismal homeostasis reflects combined, coordinated action of many cells.! 2 1!

2 The Diversity of Cells in the Human Body! Somatic cells! Sex cells! 3 Anatomy of a Representative Cell! Spotlight Figure 3-1! 4 2!

3 A Typical Cell! Is surrounded by extracellular fluid! Has a cell (plasma) membrane separates cell from its environment! Has a large surface area to volume ratio! 5 Why are cells small?! Surface area to volume ratio limits cell size.! Surface area! 1-mm cube! 6 sides x 1 2 =! 6 mm 2! 6-mm cube! 6 sides x 6 2 =! 216 mm 2! Volume! 1 3 = 1 mm 3! 6 3 = 216 mm 3! Surface area to! Volume ratio! 6/1 (6:1)! 1/1 (1:1)! 6 3!

4 ! Chapter 3 Part 2 Organelles! Importance of Surface Area to Volume Ratio! Surface area to volume ratio limits cell size because:! Cell volume determines metabolic demands! Volume increases with r 3! Cell surface area determines amount of exchange with environment (e.g. supply of O 2, nutrients)! Surface area increases with r 2! Look at the previous slide until you understand this.! Ask me again if you still don t see it.! 7 Surface area to volume ratio - 2! The bottom line is supply vs. demand:! As cell size increases, volume increases.! ü But volume increases more rapidly that surface area. ( X 3 vs. X 2 )! ü Therefore, the surface area to volume ratio decreases.! At some cell size, demand becomes greater than supply. A cell can t survive this way!! 8 4!

5 SECTION 3-1! The plasma membrane separates the cell from its surrounding environment and performs various functions! 9 Cell Membrane Functions! Physically isolates cell from environment! Regulates of exchange with the environment (semipermeable)! Recognizes/responds to environment (sensitivity)! Catalyzes chemical reactions! Provides structural support! Cell membrane is a phospholipid bilayer =! Fluid Mosaic Model of the cell membrane! 10 5!

6 The Cell (Plasma) Membrane Figure 3-2! Phospholipid bilayer with proteins, lipids and carbohydrates! 11 Membrane Lipids! By weight, lipid:protein ratio about 40%:60%! Phospholipids (about 70% - review Figure 2-18)! Polar molecules! Hydrophilic heads, hydrophobic tails! Cholesterol (about 20% - review Figure 2-17)! Increases stiffness of membrane! Glycolipids (very low %) ( glyco- = sugar)! On extracellular surface only! Adhesion molecules, identity markers! 12 6!

7 Membrane Protein Types! Positional classification:! Integral proteins! Peripheral proteins! Functional classification:! Anchoring proteins! Recognition proteins (e.g. MHC)! Enzymes! Receptor proteins (bind ligands)! Carrier proteins! Channel proteins! 13 The Cell Membrane Review of Figure 3-2! 14 7!

8 Membrane Carbohydrates Form the Glycocalyx! Types! Proteoglycans! Glycolipids! Glycoproteins (MHCs)! Functions! Lubrication and protection (structure)! Anchoring and locomotion! Reception - binding specificity! Recognition! 15 SECTION 3-2! Organelles within the cytoplasm perform particular functions! 16 8!

9 The Cytoplasm! Cytoplasm = cytosol = intracellular fluid! Varies in viscosity (thickness)! Plasmasol Plasmagel! Contains organelles and inclusions! 17 Intra- vs. Extracellular Fluid! Compared to extracellular fluid, intracellular fluid has:! A higher [K + ]! A lower [Na + ]! A higher suspended [proteins] (30% of cell weight)! Reserves! e.g., CH 2 Os, amino acids, lipids! Insoluble inclusions! glycogen granules, lipid droplets, pigments! 18 9!

10 ! Chapter 3 Part 2 Organelles! Organelles! Nonmembranous organelles are not enclosed by a membrane! e.g. Cytoskeleton, centrioles, ribosomes! Membranous organelles are surrounded by lipid membranes! e.g. Endoplasmic reticulum, Golgi apparatus, lysosomes, mitochondria, nucleus! 19 Anatomy of a Representative Cell Figure 3-1! 20 10!

11 Cytoskeleton Provides Strength and Flexibility! Functions! Structural support, cell shape! Cell movement! Organelle movement!! Types thinnest to thickest! Microfilaments! Intermediate filaments! Microtubules! Thick filament! 21 The Cytoskeleton Figure 3-3! 22 11!

12 !! Chapter 3 Part 2 Organelles! Microfilaments! Composed of actin! Functions:! Anchor cytoskeleton to integral proteins - mechanical support! Determine consistency of cytoplasm plasmagel (lots of microfilaments) plasmasol (fewer microfilaments)! Phagocytosis and cell movement/ contraction (with myosin)! 23 Intermediate Filaments! Composed of different proteins in different cells! e.g. Keratin in epithelial cells (chapter 5)! Functions: Cell shape and structure! Stabilize organelles! Cell-cell junctions! e.g. desmosomes, keratin! 24 12!

13 Microtubules! Composed of tubulin! Extend outward from centrosome! Functions:! Support, anchoring! Cell shape - movement! Organelle movement - Molecular motors! dynein, kinesins! Centrioles and spindle apparatus (cell division)! Cilia! 25 Centrioles, Centrosome and Cilia (microtubules)! Centrioles! Direct the movement of chromosomes during cell division! Organize the cytoskeleton! Centrosome = cytoplasm surrounding the centrioles! Cilia (singular = cilium)! Anchored by a basal body! Beat rhythmically to move fluids across cell surface (e.g. Respiratory system)! 26 13!

14 ! Chapter 3 Part 2 Organelles! Centrioles and Cilia Microtubules Figure 3-4! Very cool mechanism! 27 Thick Filaments! Composed of myosin! Found in muscle cells! Function: Part of contractile mechanism (Chapter 10)! Videos on my Links Page! 28 14!

15 Ribosomes! Sites of protein synthesis (translation)! Composed of a large and a small ribosomal subunit! Contain ribosomal RNA (rrna) + protein! Types:! Free ribosomes: suspended (free) in cytoplasm make proteins for use within cell cytoplasm Fixed ribosome: attached to endoplasmic reticulum protein functions listed under rough ER! 29 Proteasomes! Barrel-shaped molecules - several polypeptides! Contain proteases (enzymes)! Remove and break down damaged or abnormal proteins! Proteins to be recycled tagged with ubiquitin (An entire class of enzymes does this tagging)! Proteins amino acids, small peptides! 30 15!

16 The Endoplasmic Reticulum (ER) Figure 3-5! 31 ER: Overall Functions! 1. Synthesis! Lipids, CH 2 Os, proteins! 2. Storage! 3. Transport within cell! 4. Detoxification! 32 16!

17 Rough ER Functions! Rough ER contains fixed ribosomes! Major functions:! Make proteins for! Export from cell (secretion)! Inclusion in cell membranes! Inclusion in lysosomes! Other functions:! Intracellular transport! Temporary storage! 33 Smooth ER Functions! Smooth ER does not contain ribosomes! Vesicles transport proteins to Golgi apparatus! Synthesizes lipids (phospholipids, cholesterol, steroid hormones)! Storage area! Calcium stored inside, especially in muscle cells! Glycogen granules stored on surface! Surface area for enzymatic reactions! Glycogen free glucose! Detoxification reactions! 34 17!

18 The Golgi Apparatus Figure 3-6! Transport vesicles! from ER! 35 Golgi Apparatus Functions! Acts like the Post Office! Sorts, packages, delivers molecules Forms secretory vesicles! Discharged by exocytosis! Forms new membrane components! Packages enzymes into lysosomes! 36 18!

19 Functions of the Golgi Apparatus Figure 3-7! e.g. Natural Killer cell secreting perforin 37 Lysosomes! Contain digestive enzymes used in:! Digestion following phagocytosis or endocytosis - kiss and run, fusion! Autophagy (recycling) kiss and run, fusion! Autolysis (after cell damage, death)! (Not involved in programmed cell death : British Society for Cell Biology, January 2011)! Enzymes:! Hydrolases - digest all types of macromolecules! Maximum activity at ph near 5! Inactive in primary lysosomes, activated in secondary lysosomes! 38 19!

20 Lysosome Functions Figure 3-8! Autophagy! Autolysis! Digestion! 39 Mitochondrion (Mitochondria) Figure 3-9! All derived from mother! Contain their own DNA! Responsible for ATP production through aerobic respiration! Matrix = fluid contents of mitochondria! Cristae = folds in inner membrane! 40 20!

21 SECTION 3-3! The nucleus contains DNA and enzymes essential for controlling cellular activities! 41 The Nucleus is the Brain of the Cell! Surrounded by a nuclear envelope (double membrane)! Communicates with cytoplasm through nuclear pores! Contents of the nucleus (nucleoplasm):! Nuclear matrix! Enzymes, nucleotides (DNA, RNA), ions, etc.! One or more nucleoli! Chromatin! DNA bound to histones! Chromosomes! 42 21!

22 The Nucleus Figure 3-10! 43 Chromosome Structure Figure 3-11! 44 22!

23 ! Chapter 3 Part 2 Organelles! The Nucleolus (Nucleoli)! Region containing DNA, rrna, enzymes, histones! Synthesize ribosomal RNA (rrna)! Assemble ribosomal subunits (small and large)! Carriers transport subunits to nuclear pores! Nucleolus Nucleus 45 SECTION 3-4! DNA controls protein synthesis, cell structure, and cell function! 46 23!

24 The Genetic Code! Triplet code! Three nucleotides in sequence along a DNA strand code for one amino acid that will be added to a growing polypeptide! A gene contains all the triplets needed to code for a specific polypeptide! 47 Protein Synthesis Overview! transcription! translation! DNA! RNA! Protein! (Nucleotides)! (Nucleotides)! (Amino acids)! Transcription:! Information stays in the same language (base pair sequence)! Translation:! Information is translated from base pair sequence to amino acid sequence 48 24!

25 Gene Activation and Protein Synthesis! Gene activation begins with RNA polymerase binding to the gene (DNA) at a promoter region! Transcription is the formation of mrna from DNA! mrna carries instructions from the nucleus to the ribosome in the cytoplasm! 49 Making Proteins Requires:! Be absolutely certain that you know this slide and the next slide before you worry about other details.! 1. Instructions:! Genes on DNA in nucleus! 2. An assembly site:! Ribosomes = rrna (ribosomal RNA) + proteins in cytoplasm! And! 50 25!

26 Making Protein Requires (2)! 3. Federal Express :! mrna (messenger RNA) takes instructions from nucleus to assembly site in cytoplasm! 4. Raw materials:! Amino acids in cytoplasm! 5. Transport of raw materials to assembly site:! trna (transfer RNA) carries amino acids to ribosome! 51 DNA vs. RNA Base Pairing! mrna DNA polymerase! makes new DNA! RNA polymerase makes RNA from DNA! 52 26!

27 !! Chapter 3 Part 2 Organelles! Some Important Terms! Code - DNA! Three (3) nucleotide bases in sequence along a gene (DNA) code for one amino acid! Codon - mrna! Complementary to DNA sequence for a protein (made from DNA template strand)! Three (3) nucleotide bases along an mrna molecule code for one amino acid Anticodon - trna! Anticodon determines which amino acid the trna molecule can carry! Complementary to mrna codon(s)! 53 More Important Terms! Coding strand - DNA strand that specifies the sequence of amino acids in the new polypeptide! Template strand - DNA strand that is read by RNA polymerase to produce mrna! The template strand is complementary to the coding strand! 54 27!

28 DNA Triplets Table 3-1! AUG = START; UAA, UAG and UGA = STOP 55 Transcription! Overview slide, not from your text 56 28!

29 RNA Polymerase - 1! 57 RNA Polymerase - 2! Transcription direction DNA coils back up CODING STRAND DNA unwinds Newly-formed mrna TEMPLATE STRAND DNA template strand being read, mrna forming 58 29!

30 RNA Polymerase - 3! = RNA polymerase 59 Transcribed mrna! At end of gene:! mrna transcript is released from RNA polymerase ( Release Factor inserted)! Post-transcriptional modification occurs 60 30!

31 ! Chapter 3 Part 2 Organelles! Post-transcriptional Modifications to mrna! Introns = intervening sequences! Cut out while mrna is in nucleus! Not expressed in protein! May be evolutionary baggage! Exons = expressed portion of mrna! Spliced together after introns cut out! 61 Post-transcriptional Modifications - 2! 5ʹ cap = modified G (guanine) nucleotides! Protects mrna from digestion (for a while)! Says attach here to ribosome! Poly-A tail = adenines! Protects mrna from digestion! May help guide mrna out of nucleus! 62 31!

32 The Triplet Code! Transcription by RNA Polymerase! Amino acid 1 Amino acid 2 Amino acid 3 Amino acid 4 Amino acid 5 63 Translation! The mrna codon (nucleotide sequence) is translated into a polypeptide (amino acid sequence)! Takes place in cytoplasm! Involves:! mrna (codon)! Ribosome (assembly site)! trnas (anticodons)! Amino acids! 64 32!

33 Transfer RNAs (trnas)! Composed of nucleotides (like all RNAs)! Carry amino acids to ribosome! Which amino acid is carried is determined by a trna s anticodon! Anticodon is complementary to specific mrna codon(s)! 65 In-class Protein Synthesis! The bringing together of all of these parts is a synthesis of its own.! Starting with a gene (DNA), we will go through the steps of protein protein synthesis on the board in lecture room.! You may also want to look at the diagrams in the text, pp ! Protein synthesis links from Links Page:! Protein synthesis animation on YouTube! Transcription and translation video! 66 33!