The Cell – Structure, and Functions (Synopsis Points) – This is the basic points of the Cell. This point helps to review your basics. Just read carefully. This points made from previous topics in this blog.

The Cell - Structure and Functions (basic synopsis)

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I. All Organisms are Made up of Cells

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  • The cell is the basic unit of structure & function.
  • The cell is the smallest unit that can still carry on all life processes.
  • Both unicellular (one-celled) and multicellular (many-celled) organisms are composed of cells.
  • Before the 17th century, no one knew cells existed.
  • Most cells are too small to be seen with the unaided eye.
  • In the early 17th century microscopes were invented & cells were seen for the 1st time.
  • Anton Von Leeuwenhoek, a Dutchman, made the 1st hand-held microscope & viewed microscopic organisms in water & bacteria from his teeth.
  • In 1665, an English scientist named Robert Hooke made an improved microscope and viewed thin slices of cork viewing plant cell walls.
  • Hooke named what he saw “cells”.
  • In the 1830’s, Matthias Schleiden (botanist studying plants) & Theodore Schwann (zoologist studying animals) stated that all living things were made of cells.
  • In 1855, Rudolf Virchow stated that cells only arise from pre-existing cells.
  • Virchow’s idea contradicted the idea of spontaneous generation (the idea that nonliving things could give rise to organisms).
  • The combined work of Schleiden, Schwann, & Virchow is known as the Cell Theory.

 

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II. Principles of the Cell Theory

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  • All living things are made of one or more cells
  • Cells are the basic unit of structure & function in organisms
  • Cells come only from the reproduction of existing cells

 

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III. Cell Diversity

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  • Not all cells are alike
  • Cells differ in size, shape, and function
  • The female egg cell is the largest cell in the body & can be seen without a microscope
  • Bacterial cells are some of the smallest cells & are only visible with a microscopeRelative sizes of cells and their components
  • Cells need surface area of their cell membrane large enough to adequately exchange materials with the environment (wastes, gases such as O2 & CO2, and nutrients)
  • Cells are limited in size by the ratio between their outer surface area & their volume
  • Small cells have more surface area for their volume of cytoplasm than large cells
  • As cells grow, the amount of surface area becomes too small to allow materials to enter & leave the cell quickly enough

cell size and its dimensions

  • Cell size is also limited by the amount of cytoplasmic activity that the cell’s nucleus can control
  • Cells come in a variety of shapes, & the shape helps determine the function of the cell (e.g. Nerve cells are long to transmit messages in the body, while red blood cells are disk-shaped to move through blood vessels)

cell types in eukaryotes

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IV. Prokaryotes

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  • Prokaryotic cells are less complex
  • Unicellular
  • Do not have a nucleus & any membrane-bound organelles
  • Most have a cell wall surrounding the cell membrane & a single, looped chromosome (genetic material) in the cytoplasm
  • Include bacteria & blue-green bacteria
  • Found in the kingdom Monera

Prokaryotic cell structure

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V. Eukaryotes

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  • More complex cells
  • Includes both unicellular & multicellular organisms
  • Do have a true nucleus & membrane-bound organelles
  • Organelles are internal structures in cell’s that perform specific functionsshapes of Cell and organelles
  • Organelles are surrounded by a single or double membrane
  • Entire eukaryotic cell surrounded by a thin cell membrane that controls what enters & leaves the cell
  • Nucleus is located in the center of the cell
  • The nucleus contains the genetic material (DNA) & controls the cell’s activities
  • Eukaryotes include plant cells, animal cells, fungi, algae, & protests
  • Prokaryotes or bacteria lack a nucleus
  • Found in the kingdoms Protista, Fungi, Plantae, & Animalia

Eukaryotic cell structure

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VI. Cell Membrane

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  • Separates the cytoplasm of the cell from its environment
  • Protects the cell & controls what enters and leaves
  • Cell membranes are selectively permeable only allowing certain materials to enter or leave
  • Composed of a lipid bilayer made of phospholipid molecules
  • The hydrophilic head of a phospholipid is polar & composed of a glycerol & phosphate group and points to the aqueous cytoplasm and external environment.
  • The two hydrophobic tails are nonpolar point toward each other in the center of the membrane & are composed of two fatty acids

Cell membrane structure

  • When phospholipids are placed in water, they line up on the water’s surface with their heads sticking into the water & their tails pointing upward from the surface.
  • The inside of the cell or cytoplasm is an aqueous or watery environment & so is the outside of the cell. Phospholipid “heads” point toward the water.
  • Phospholipid “tails” are sandwiched inside the lipid bilayer.
  • The Cell - Structure and Functions (Synopsis Points) The cell membrane is constantly breaking down & being reformed inside living cells.
  • Certain small molecules such as CO2, H2O, & O2 can easily pass through the phospholipids
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VII. Membrane Proteins

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  • A variety of protein molecules are embedded in the cell’s lipid bilayer.
  • Some proteins called peripheral proteins are attached to the external & internal surface of the cell membrane
  • Integral proteins or transmembrane proteins are embedded & extend across the entire cell membrane. These are exposed to both the inside of the cell & the exterior environment.
  • Other integral proteins extend only to the inside or only to the exterior surface.
  • Cell membrane proteins help move materials into & out of the cell.
  • Some integral proteins called channel proteins have holes or pores through them so certain substances can cross the cell membrane.
  • Channel proteins help move ions (charged particles) such as Na+, Ca+, & K+ across the cell membrane
  • Transmembrane proteins bind to a substance on one side of the membrane & carry it to the other side. e.g. glucose
  • Some embedded, integral proteins have carbohydrate chains attached to them to serve as chemical signals to help cells recognize each other or for hormones or viruses to attach
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VIII. Fluid Mosaic Model

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  • The phospholipids & proteins in a cell membrane can drift or move side to side making the membrane appear “fluid”.
  • The proteins embedded in the cell membrane form patterns or mosaics.
  • Because the membrane is fluid with a pattern or mosaic of proteins, the modern view of the cell membrane is called the fluid mosaic model.

fluid mosaic model

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IX. Internal Cell Structure & Organelles of Eukaryotes

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  • Cytoplasm includes everything between the nucleus and cell membrane.
  • Cytoplasm is composed of organelles & cytosol (jellylike material consisting of main water along with proteins.
  • Eukaryotes have membrane-bound organelles; prokaryotes do not.

Cell Organelles table

  • Mitochondria are large organelles with double membranes where cellular respiration (breaking down glucose to get energy) occurs
    • Energy from glucose is used to make ATP or adenosine triphosphate
    • Cells use the ATP molecule for energy
    • More active cells like muscle cells have more mitochondria
    • Outer membrane is smooth, while inner membrane has long folds called cristae
    • Have their own DNA to make more mitochondria when needed

Mitochondria outer line structure

  • Ribosomes are not surrounded by a membrane & are where proteins are made in the cytoplasm (protein synthesis)
    • Most numerous organelle
  • Endoplasmic Reticulum
    • May be free in the cytoplasm or attached to the rough ER (endoplasmic reticulum)
    • Endoplasmic reticulum is membranous tubules & sacs that transport molecules from one part of the cell to another
    • Smooth ER lacks ribosomes & helps break down poisons, wastes, & other toxic chemicals
    • Smooth ER also helps process carbohydrates & lipids (fats).
    • The ER network connects the nucleus with the cell membraneEndoplasmic reticulum

rough ER in ribosomesG. Golgi Apparatus modifies, packages, & helps secrete cell products such as proteins and hormones

  • Consists of a stack of flattened sacs called cisternae
  • Receives products made by the ER

The cell - structure and functions (Synopsis points)

H. Lysosomes are small organelles containing hydrolytic enzymes to digest materials for the cell

  • Single membrane
  • Formed from the ends of Golgi that pinch off
  • Found in most cells except plant cells

I. Cytoskeleton consists of a network of long protein tubes & strands in the cytoplasm to give cells shape and helps move organelles

  • Composed of 2 protein structures — microtubules, intermediate filaments, & microfilaments
  • Microfilaments are rope-like structures made of 2 twisted strands of the protein actin capable of contracting to cause cellular movement (muscle cells have many microfilaments)
  • Microtubules are larger, hollow tubules of the protein called tubulin that maintain cell shape, serve as tracks for organelle movement, & help cells divide by forming spindle fibers that separate chromosome pairs

J. Cilia are short, more numerous hair-like structures made of bundles of microtubules to help cells move

1. Line respiratory tract to remove dust & move paramecia

The cell - structure and functions (Synopsis points)

K. Flagella are long whip-like tails of microtubules bundles used for movement (usually 1-3 in number) –  Help sperm cells swimming to reach ovule.

L. Nucleus (nuclei) in the middle of the cell contains DNA (hereditary material of the cell) & acts as the control center

  • Most cells have 1 nucleolus, but some have several
  • Has a protein skeleton to keep its shape
  • Surrounded by a double layer called the nuclear envelope containing pores
  • Chromatin is the long strand of DNA in the nucleus, which coils during cell division to make chromosomes
  • Nucleolus (nucleoli) inside the nucleus makes ribosomes & disappears during cell division

Structure of Nucleus

M. Cell walls are nonliving, protective layers around the cell membrane in plants, bacteria, & fungi

cell wall (Microscopic view)

  • Fungal cell walls are made of chitin, while plant cell walls are made of cellulose
  • Consist of a primary cell wall made first and a woody secondary cell wall in some plants

N. Vacuoles are the largest organelle in plants taking up most of the space

  1. Serves as a storage area for proteins, ions, wastes, and cellular products such as glucose
  2. May contain poisons to keep animals from eating them
  3. Animal vacuoles are smaller & used for digestion

O. Plastids in plants make or store food & contain pigments to trap sunlight

  • Chloroplast is a plastid that captures sunlight to make O2 and glucose during photosynthesis; contains chlorophyll
    • Double membrane organelle with an inner system of membranous sacs called thylakoids
    • Thylakoids made of stacks of grana containing chlorophyll
  • Other plastids contain red, orange, and yellow pigments
  • Found in plants, algae, & seaweed

The cell - structure and functions (Synopsis points)

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X. Multicellular Organization

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  • Cells are specialized to perform one or a few functions in multicellular organisms
  • Cells in multicellular organisms depend on each other
  • The levels of organization include:

Cells –> Tissues –> Organs –> Systems –> Organism

  • Tissues are groups of cells that perform a particular function (e.g. Muscle)
  • Organs are groups of tissues working together to do a job (e.g. heart, lungs, kidneys, brain)
  • Systems are made of several organs working together to carry out a life process (e.g. Respiratory system for breathing)
  • Plants have specialized tissues & organs different from animals
  • Dermal tissue forms the outer covering of plants
  • Ground tissue makes up roots & stems
  • Vascular tissue transports food & water
  • The four plant organs are the root, stem, leaf, & flower
  • Colonial organisms are made of cells living closely together in a connected group but without tissues & organs (e.g. Volvox).

Source: Reference Notes