sign in sign up
<<
Home , Endomembrane system, Membrane transport

, and Cell Transport Cell Theory 4 basic concepts of cell theory are: Cells are the units of structure (building blocks) of all animals and plants. Cells are the smallest unit of function in all animals and plants. Cells originate only from pre-existing cells by cell division. All cells maintain homeostasis

Cell Cell – Cell-membrane, and Nucleus

Cytoplasm – and Cell

Nucleus – , Nucleoplasm and (DNA + ) All cells are covered with a thin covering of a double layer of and associated present here and there. Each has a polar (hydrophilic) head and non-polar (hydrophobic) tails. In the double layer the tails face each other forming a hydrophobic barrier which keeps dissolved contents inside. Proteins may be Intrinsic – embedded in the lipid double layer and Extrinsic associated outside the lipid double layer.

Cytoplasm Cytoplasm is the living fluid part between cell membrane and nucleus. It has special structures called Cell Organelles in it. Cytosol is the matrix (formless) part of cytoplasm formed of water having dissolved or suspended substances in it. Cell Organelles are organ like each performing specific function/s but formed of and only (sub-cellular). Double Membrane bound Organelles: Mitochondria, , Golgi Body, and Nucleus. Single Membrane bound Organelles: , , Organelles lacking any membrane: , , Nucleus and Ribosomes 1 Genetic Control of the : is the most distinct structure inside cell visible with light microscope. It has inside it DNA having all the information needed to form and run the cell. The segments of DNA are called Genes. Nuclear Envelope: is formed of 2 membranes with a gap between them. It has a large number of Nuclear Pores usually bound by a nuclear complex. The pores are large enough to allow RNA and proteins to pass through. Nucleoplasm: is the matrix (formless) of nucleus and has a different composition than Cytosol. Chromatin fibers: are very long molecules of DNA associated with proteins (Histones and other nuclear proteins). Each chromatin fiber, at the time of cell division, organizes into Chromosomes. Nucleolus: is present in the nucleus when the cell is not dividing. No membrane bounds it. It assembles both units of Ribosomes. Nucleus and Ribosomes 2 Ribosomes are the smallest in cells. Ribosomes are the site of synthesis.

Each has 2 sub-units larger (60S) and smaller (40S).

r-RNA and ribosomal proteins form the ribosomal subunits.

No membrane covers the ribosomal subunits. Ribosomal subunits join only around m-RNA for protein synthesis otherwise remain separate.

The Endomembrane System 1 Manufacturing and Distributing Cellular Products Endoplasmic Reticulum, , Lysosomes and Vacuoles collectively form Endomembrane System. Endoplasmic Reticulum: is a system of double membranes in the form of tubes and sacs throughout cytoplasm (in between cell membrane and nuclear envelope). ER is main manufacturing facility. Functions include synthesis of proteins and lipids including , detoxification, and cellular transportation. It transports RER SER materials inside the cell by 1. Rough ER, ribosome fixed 1. Smooth ER, no ribosome fixed transport vesicles. 2. Flat sacs 2. Tubular sacs 3. Synthesis of membrane proteins 3. Synthesis of Lipids, steroids

4. Synthesis of secretory proteins 4. Detoxification of drugs The Endomembrane System 2 Golgi Apparatus = Golgi Body: is a stacks of flattened sacs called cisternae. A cell may have from a few to a few hundred of Golgi stacks. Golgi Apparatus receives transport vesicles from ER on one side, modifies received chemicals, can store them and packs them in secretory vesicles and releases them on shipping side. Lysosomes: are single membrane bound organelles rich in digestive , help in breakdown of large molecules like proteins, polysaccharides, lipids and nucleic acids. Lysosomes provide a safe place for digestion of large molecules without damaging molecules of the cell. A joins a food to digest the materials inside vacuole. Lysosomes are absent in most plant cells. Mitochondria Energy Conversion Mitochondria (sing. ): are the powerhouses of cells and the site for cellular respiration. Respiration is oxidation of food and chief source of energy for the cell. These are bound with double membrane, outer smooth and inner folded. Mitochondria have enzymes for breakdown derivatives, fatty acids and amino acids. Mitochondria have Electron-Transport-System that generates ATP molecules by using the energy contained in H’s produced during breakdown of glucose. The Cell Shape and Movement Maintaining Cell Shape: The shape of the cell is maintained by Intermediate Filaments, the thick ropes of twisted protein fibers, , the hollow organelles and , the solid thin organelles. These maintain the shape of cells and keep in position the nucleus. The framework of support is highly dynamic that can organize and dismantle really fast. Transport of organelles and molecules: Microtubules are the freeways used by organelles like lysosomes to move from one part of cell to another. Microfilaments are the roads/streets used by smaller things. Recap-1 Chapter-3 1. The liquid part of cytoplasm is ------2. Structures formed of membranes and molecules, present in cytoplasm, doing a special function, are ------3. 2 halves of cell membrane are held together by ------bonds 4. Cell membrane is fluid due to ------molecules 5. Membrane bound ------molecules regulate membrane transport 6. Smooth E.R. synthesizes ------7. Rough E.R. synthesizes ------8. Golgi Apparatus is the ------of the cell and produces secretory vesicles. 9. ATP’s are synthesized in the ------chamber of ------. 10. Single membrane bound organelle rich in digestive enzymes is ----- 11. Double membrane bound organelle with DNA are ------12. -----are hollow cylinders and help in transporting vesicles in cell

Cellular Reproduction = Cell Division Passes on Genes from Cells to Cells Reproduction of Organisms Genes – DNA – Chromatin fiber – Chromosomes Genes, the segments of DNA, are part of chromatin fiber found in nucleus. Chromatin fiber is formed of DNA and proteins. Most of the time the chromatin fibers exist as a diffuse network (not visible even under ). However, when the cell starts to divide the chromatin fibers organize into compact threads called Chromosomes. Each species has a fixed # of chromosomes – 46 in most human cells. Chromosome – DNA – Gene Almost all the eukaryotic genes (about 20000 in human genes) are found in the chromosomes. Some genes are present in Mitochondria. DNA spools around basic proteins Histones to form chromatin. Chromatin packs to form thicker threads Chromatids. A chromosome has 1 or 2 Chromatids in it. A chromosome with 1 chromatid divides to form a chromosome with 2 Chromatids (sister). One chromatid is passed on to each daughter cell.

Cell Cycle Cell Cycle: Most cells in body divide though at different rates. There are 2 distinct phases that alternate with each other and form a cell-cycle. M-phase: when a cell is dividing. The daughter cells are half in size. Interphase: Each daughter cell must grow by making new materials including proteins and DNA. Interphase is divided into 3 sub-phases : G1, S and G2. S-phase occurs in the middle part of Interphase and DNA replication takes place. DNA and chromosomes are doubled. G1 and G2 are growth phases of cell with synthesis of proteins and ribosome. G1 takes place before S-phase. But G2 occurs after the S-phase. Mitosis The cell division of growth and maintenance Mitosis is the division of growth and replacement of lost or damaged cells. Mitosis is division of nucleus and Cytokinesis is division of cytoplasm. Just before the end of interphase 2 centrioles divide into 4 centrioles. Mitosis has 4 distinct phases Prophase, Metaphase, Anaphase and Telophase. Memory aid: P-MAT Mitosis – Prophase pro = first Prophase: is the phase that prepares the cell for mitosis. start moving to opposite ends and spindle formation starts. Chromatin packs into thick threads Chromosomes. In late prophase nuclear envelope degenerates and chromosomes are released in cytoplasm. Spindle fibers either join a spindle fiber from the opposite or connect to the centromere of a chromosome. Mitosis – Metaphase meta = after Metaphase: The spindle is fully formed now. The chromosome pack further and get most distinct. Chromosomes arrange on an imaginary disc = equatorial plate at the middle. The centromeres of chromosomes lie at the plate. Each centromere is joined through spindle fibers to both centrosomes. Mitosis – Anaphase ana = apart Anaphase: is the movement of young chromosomes from the middle towards respective poles (centrosomes). It starts suddenly when the centromeres divide. Each chromosome is formed only of 1 chromatid. The motor proteins at centromeres move the chromosomes on the microtubules of spindle fibers. Telophase telo = end Telophase begins when the 2 groups of chromosomes reach the poles. This phase is the reverse of prophase. Chromosomes unpack to diffuse network. Nuclear envelope is reorganized from Endoplasmic Reticulum. Spindle fibers disappear. One nucleus is completely divided into 2 genetically similar daughter nuclei. Cytokinesis kinesis = motion Cytokinesis takes place along Telophase. In an animal cell cleavage furrow appears at the middle and divides the cytoplasm into 2 equal halves, each with a nucleus. In a plant cell a cell-plate is formed at the middle. Golgi apparatus provides most of the materials packed in vesicles. Cell plate starts at the center and proceeds towards parent . Cell plate joins with the parental cell wall to complete the Cytokinesis. Most plant cells lack centrioles in them and centrosomes organize spindle formation. Recap-2 Chapter-3 1. Synthesis of DNA takes place during ------of cell cycle. 2. When cell is not dividing DNA occurs in the form of ------3. When the cell is dividing the DNA occurs in the form of ------4. Spindle fibers are made of ------5. In prophase and metaphase chromosome has ------chromatid/s 6. In anaphase and Telophase chromosome has -----chromatid/s 7. During ------chromosomes arrange on mid-plate in mitosis 8. Division of cytoplasm after mitosis is called ------9. Divided chromosomes move to opposite poles during ------10. Spindle is formed, chromosomes appear randomly arranged and nuclear envelope breaks during ------11. Nuclear envelope appears, chromosomes unpack during ------Diploid and Haploid cells Diploid cells have 2 sets of chromosomes Most body cells in humans have 46 chromosomes – Diploid (2n) Haploid cells have 1 set of chromosomes Sperms and eggs in humans have 23 chromosomes – Haploid (n) Cell Membrane and Transport Semi-permeable: Cell membranes allow some materials to pass through them and prevent others from doing so. Regulators like hormones can change permeability of a cell membrane. Transport across membrane can be Passive or Active. RER SER

1. Rough ER, ribosome fixed 1. Smooth ER, no ribosome fixed

2. Flat sacs 2. Tubular sacs

3. Synthesis of membrane proteins 3. Synthesis of Lipids, steroids

4. Synthesis of secretory proteins 4. Detoxification of drugs

Passive Transport includes , and . Diffusion: All fluids (liquids + gases) move from area of higher to area of lower concentration (concentration gradient). This movement of substances is called Diffusion. It can be through cell membranes. For example, spreading of fragrance, dissolving of ink drop in water, movement of O2 and CO2 between lungs and blood. Osmosis is always the net movement of water through cell membrane from its higher concentration (dilute ) to its lower concentration (concentrated solution) when the 2 are separated by semi-permeable membrane. For example, absorption of water by roots of plants. Facilitated diffusion is faster than normal diffusion but needs a carrier protein though no ATP needed. For example, absorption of glucose and amino acids in intestine.

Diffusion versus Osmosis RER SER

1. Rough ER, ribosome fixed 1. Smooth ER, no ribosome fixed

2. Flat sacs 2. Tubular sacs

3. Synthesis of membrane proteins 3. Synthesis of Lipids, steroids

4. Synthesis of secretory proteins 4. Detoxification of drugs

Active Transport Only can operate against concentration gradient. It is the fastest mode of transport. Fig 3-9, Na+ - K+ pump It always consumes ATP directly or indirectly. It always needs one or more transport proteins. For example absorption of minerals by plant roots, absorption of nutrients when their concentration is already higher inside the cells.

Vesicular Transport Large molecules like proteins cannot transport through membrane by passive or active transport discussed so far. These are packed into membrane bound sacs and transported across cell membrane. is the bulk transport into the cell in a membrane bound vesicle. is bringing solids in a vesicle. For example, white blood cells eat bacteria. is bringing in liquid bound in sac the process is called. : When the cells releases solid or liquid in sacs the process is called exocytosis. For example, gland cells secrete hormones by sending secretory vesicles to cell membrane. Recap 3 Cell Transport 1. Movement of solute from high to low concentration is ------2. Net Movement of water across cell membrane (from low concentration solution to high concentration solution) is ------3. ------can operate against concentration gradient and needs both a carrier protein and ATP. 4. ------moves along the concentration gradient and needs a carrier protein but no ATP. 5. Vesicular transport of solids into the cell in a vesicle is ------and of liquids is ------6. Movement of water is A  B or B  A

A. 5.2% glucose solution B. 3.5 % glucose solution

7. Eating of bacteria by a White Blood Cell is ------

Protein Synthesis 2 main processes occur during protein synthesis. Transcription Translation DNA ------m-RNA ------Protein Transcription: Cell uses information in DNA to form m-RNA in presence of RNA polymerase and special proteins. It takes place inside nucleus and m-RNA leaves through nuclear pores to enter cytoplasm. Translation: 2 sub-units of ribosome attach at one end of m-RNA. Then, t-RNA molecules bring required amino acids to ribosome/m-RNA complex. Codon of m-RNA and anticodon of t-RNA need to be complementary to get incorporated in polypeptide chain. As ribosome moves over m-RNA, a new is added to the chain at each step. Polypeptide chain undergoes coiling to get specific 3-D shape of protein. Recap 4 Protein Synthesis 1. DNA  m-RNA is ------2. m-RNA  protein is ------3. Translation takes place in ------4. Transcription takes place in ------5. t-RNA brings ------to m-RNA-ribosome complex 6. A ------is a triplet of N-bases of m-RNA and has information for 1 amino acids. 7. In DNA adenine binds to ------8. In DNA cytosine binds to ------