Download Cell, Mitosis and Cell Membrane Transport

Cell, Mitosis and Cell Membrane 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, Cytoplasm and Nucleus
Cytoplasm – Cytosol and Cell Organelles
Nucleus – Nuclear Envelope, Nucleoplasm and Chromatin (DNA + Histones)
Cell Membrane
All cells are covered with a thin covering of a double layer of Phospholipids and associated Proteins
present here and there.
Each phospholipid 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 water 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 molecules and
membranes only (sub-cellular).
Double Membrane bound Organelles: Mitochondria, Endoplasmic Reticulum, Golgi Body, and Nucleus.
Single Membrane bound Organelles: Lysosomes, Peroxisomes, Vacuoles
Organelles lacking any membrane: Ribosomes, Centrioles, Nucleolus
Nucleus and Ribosomes 1
Genetic Control of the Cell
Nucleus: 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 organelle in cells. Ribosomes are the site of protein synthesis.
Each ribosome 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, Golgi Apparatus, 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 steroids, detoxification, and cellular
transportation. It transports
RER
SER
materials inside the cell by
transport vesicles.
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
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 enzymes, 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 Lysosome joins a food
vacuole to digest the materials inside vacuole. Lysosomes are absent in most plant cells.
Mitochondria
Energy Conversion
Mitochondria (sing. Mitochondrion): 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 glucose 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 Cytoskeleton
Cell Shape and Movement
Maintaining Cell Shape: The shape of the cell is maintained by Intermediate Filaments, the thick ropes
of twisted protein fibers, Microtubules, the hollow organelles and Microfilaments, 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 Histone proteins.
Most of the time the chromatin fibers exist as a diffuse network (not visible even under electron
microscope).
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.
Centrosomes 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 centrosome 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 wall.
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
Passive Transport includes Diffusion, Osmosis and Facilitated Diffusion.
Diffusion: All fluids (liquids + gases) move from area of higher concentration 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 solution) to its lower concentration (concentrated solution) when the 2 solutions 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.
RER
Diffusion versus Osmosis
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 active transport 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.
Endocytosis is the bulk transport into the cell in a membrane bound vesicle. Phagocytosis is bringing
solids in a vesicle. For example, white blood cells eat bacteria. Pinocytosis is bringing in liquid bound in
sac the process is called.
Exocytosis: 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 enzyme 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 amino
acid 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 --------