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General cell Structure

Structure / April 25, 2018

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Cell structure[edit]

What is a cell? The word cell comes from the Latin word "cella", meaning "small room", and it was first coined by a microscopist observing the structure of cork. The cell is the basic unit of all living things, and all organisms are composed of one or more cells. Cells are so basic and critical to the study of life, in fact, that they are often referred to as "the building blocks of life". Organisms - bacteria, amoebae and yeasts, for example - may consist of as few as one cell, while a typical human body contains about a trillion cells.

According to Cell Theory, first proposed by Schleiden and Schwann in 1839, all life consists of cells. The theory also states that all cells come from previously living cells, all vital functions (chemical reactions) of organisms are carried out inside of cells, and that cells contain necessary hereditary information to carry out necessary functions and replicate themselves. It is the basis of human life.

All cells contain:

Lipid bilayer boundary (plasma membrane) Cytoplasm DNA (hereditary information) Ribosomes for protein synthesis

Eukaryotic cells also contain:

At least one nucleus Mitochondria for cell respiration and energy

Cells may also contain:

Lysosomes Peroxisomes Vacuoles Cell walls


Plasma Membrane Phospholipid bilayer, which contains great amount of proteins, the most important functions are the following:
    It selectively isolates the content of the cell of the external atmosphere. It regulates the interchange of substances between the cytoplasm and the environment. Communicates with other cells.
Model of the fluid mosaic Describes the structure of the plasma membrane, this model was developed in 1972 by cellular biologists J. Singer and L. Nicholson. Phospholipid bilayer Is in the plasma membrane and produces the fluid part of membranes. Proteins Long chains of amino acids. Glucose proteins Proteins together with carbohydrates in the plasma membrane, mostly in the outer parts of the cell. Functions of proteins Transport oxygen, they are components of hair and nails, and allow the cell interact with its environment. Transport Proteins Regulate the movement of soluble water molecules, through the plasma membrane. Some transport proteins called channel proteins form pores or channels in the membrane so that water soluble molecules pass. Carrying proteins Have union sites that can hold specific molecules. Reception proteins They activate cellular responses when specific molecules join. Proteins of recognition They work as identifiers and as place of union to the cellular surface. Fluid It is any substance that can move or change of form. Concentration Number of molecules in a determined unit of volume. Gradient Physical difference between two regions of space, in such a way that the molecules tend to move in response to the gradients. Diffusion Movement of the molecules in a fluid, from the regions of high concentration to those of low concentration. Passive transport Movement of substances in a membrane that doesn’t need to use energy. Simple diffusion Diffusion of water, gases or molecules across the membrane. Facilitated diffusion Diffusion of molecules across the membranes with the participation of proteins. Osmosis Diffusion of the water across a membrane with differential permeability. Transport that needs energy Movement of substances across a membrane generally in opposition to a gradient of concentration with the requirement of energy. Active transport Movement of small molecules using energy (ATP). Endocytosis Movement of big particles towards the interior of the cell using energy. The cells enclose particles or liquids. Pinocytosis (Literally cell drinking) Form in which the cell introduces liquids. Phagocytosis Way of eating of the cells. It feeds in this case of big particles or entire microorganisms. Pseudopodia False feet (the amoeba). Exocytosis Movement of materials out of the cell with the use of energy. It throws waste material. Isotonic The cytoplasm fluid of the interior of the cells is the same that the outer. Hypertonic solution The solutions that have a higher concentration of dissolved particles than the cellular cytoplasm and that therefore water of the cells goes out with osmosis. Hypotonic The solutions with a concentration of dissolved particles lower than the cytoplasm of a cell and that therefore do that water enters the cell with osmosis. Swelling Pressure of the water inside the vacuole. Endoplasmic Reticulum It is the place of the synthesis of the cellular membrane.

Structure and function of the cell[edit]

Rudolf Virchow Zoologist, who proposed the postulates of the cellular theory, observes that the living cells could grow and be in two places at the same time, he proposed that all the cells come from other equal cells and proposed 3 postulates:
    Every living organism is formed from one or more cells The smallest organisms are unicellular and these in turn are the functional units of the multicellular organisms. All the cells come from preexisting cells.

Common characteristics of all the cells[edit]

Molecular components Proteins, amino acids, lipids, sweeten, DNA, RNA. Structural components Plasmatic membrane, citoplasm, ribosomes. Robert Hooke He postuled for the first time the term cell Prokaryotes Their genetic material is not enclosed in a membrane ex. Bacterias Eukaryotes Their genetic material is contained inside a nucleus closed by a membrane

History of cell knowledge[edit]

The optical microscope was first invented in 17th century. Shortly thereafter scientists began to examine living and dead biological tissues in order to better understand the science of life. Some of the most relevant discovery milestones of the time period include:

The invention of the microscope, which allowed scientists for the first time to see biological cells Robert Hooke in 1665 looked at cork under a microscope and described what he called cork "cells" Anton van Leeuwenhoek called the single-celled organisms that he saw under the microscope "animalcules" Matthias Jakob Schleiden, a botanist, in 1838 determined that all plants consist of cells Theodor Schwann, a zoologist, in 1839 determined that all animals consist of cells Rudolf Virchow proposed the theory that all cells arise from previously existing cells

In 1838, the botanist Matthias Jakob Schleiden and the physiologist Theodor Schwann discovered that both plant cells and animal cells had nuclei. Based on their observations, the two scientists conceived of the hypothesis that all living things were composed of cells. In 1839, Schwann published 'Microscopic Investigations on the Accordance in the Structure and Growth of Plants and Animals', which contained the first statement of their joint cell theory.

Cell Theory[edit]

Schleiden and Schwann proposed spontaneous generation as the method for cell origination, but spontaneous generation (also called abiogenesis) was later disproven. Rudolf Virchow famously stated "Omnis cellula e cellula"... "All cells only arise from pre-existing cells." The parts of the theory that did not have to do with the origin of cells, however, held up to scientific scrutiny and are widely agreed upon by the scientific community today.

The generally accepted portions of the modern Cell Theory are as follows: (1) The cell is the fundamental unit of structure and function in living things. (2) All organisms are made up of one or more cells. (3) Cells arise from other cells through cellular division. (4) Cells carry genetic material passed to daughter cells during cellular division. (5) All cells are essentially the same in chemical composition. (6) Energy flow (metabolism and biochemistry) occurs within cells.


Allow greater resolution, can see finer detail Eye: resolution of ~ 100 μm Light microscope: resolution of ~ 200 nm Limited to cells are larger organelles within cells Confocal microscopy: 2 dimension view Electron microscope: resolution of ~0.2 nm Laser tweezers: move cell contents

Cell size[edit]

One may wonder why all cells are so small. If being able to store nutrients is beneficial to the cell, how come there are no animals existing in nature with huge cells? Physical limitations prevent this from occurring. A cell must be able to diffuse gases and nutrients in and out of the cell. A cell's surface area does not increase as quickly as its volume, and as a result a large cell may require more input of a substance or output of a substance than it is reasonably able to perform. Worse, the distance between two points within the cell can be large enough that regions of the cell would have trouble communicating, and it takes a relatively long time for substances to travel across the cell.

That is not to say large cells don't exist. They are, once again, less efficient at exchanging materials within themselves and with their environment, but they are still functional. These cells typically have more than one copy of their genetic information, so they can manufacture proteins locally within different parts of the cell.

Key concepts: Cell size:

Is limited by need for regions of cell to communicate Diffuse oxygen and other gases Transport of mRNA and proteins Surface area to volume ratio limited Larger cells typically: Have extra copies of genetic information Have slower communication between parts of cell

Structure of Eukaryotic cells[edit]

Eukaryotic cells feature membrane delimited nucleii containing two or more linear chromosomes; numerous membrane-bound cytoplasmic organelles: mitochondria, RER, SER, lysosomes, vacuoles, chloroplasts; ribosomes and a cytoskeleton. Also, plants, fungi, and some protists have a cell wall.

Structure of the nucleus[edit]

The nucleus is the round object in the cell that holds the genetic information (DNA) of the cell. It is surrounded by a nuclear envelope and has a nucleolus inside.