Cells and tissue Flashcards
Cells
Smallest living unit of an organism.
Made up of chemicals (atoms and molecules).
Similar cells combine to make tissue.
Two general classes of cells
Sex cells (ovum and sperm).
Somatic cells (every other cell in the body
Regions of Somatic cells
Intercellular: inside the cells
Extracellular: outside the cell
Main components of a somatic cell
Nucleus (control centre)
Plasma membrane (outer boundary)
Cytoplasm (everything in between the nucleus and the plasma membrane)
Plasma membrane
The physical barrier between the intercellular (cytoplasm) and extracellular environments.
The plasma membrane is made of a phospholipid bilayer (two layers of phospholipids) that is very thin. In each half of the phospholipid bilayer, the phospholipids lie with their hydrophilic (water loving) heads at the membrane surface and their hydrophobic (water hating) tails on the inside; this structure thereby protects the hydrophobic tails from being exposed to water. The hydrophobic layer in the centre of the plasma membrane isolates the cytoplasm from the extracellular fluid. It is important that this isolation is maintained as the composition of the cytoplasm is very different from that of the extracellular fluid.
It’s responsible for regulating the exchange of substances between these environments.
The plasma membrane is 42% lipids. Phospholipids form a bilayer, also known as a double layer, where the exterior surfaces are hydrophilic or also known as water loving, and the interior surfaces are hydrophobic, or fearful of water.
The plasma membrane is 5% proteins. These can be integral, or transmembrane proteins which span the membrane and can be receptors, carriers, or channels. These can also be peripheral proteins, which are bound to the inner or outer surface of the membrane, and function to anchor enzymes.
The plasma membrane is 3% carbohydrates. These form complex molecules such as glycolipids, and glycoproteins. These function in lubrication, protection, anchoring, and cell movement.
The cytoplasm
The cytoplasm consists of the cytosol and organelles.
The cytosol is the fluid inside the cell, and contains dissolved ions, nutrients, proteins, and waste products of the cell.
The organelles are the structures in the cell that are suspended in the cytosol. Each organelle has a specific function:
-The mitochondrion
-The smooth endoplasmic reticulum
-Ribosomes
-The rough endoplasmic reticulum
-The Golgi Apparatus
-The peroxisomes
-The secretory vesicles
-The lysosomes
-The centrioles
-The microtubules
The mitochondrion
The mitochondrion is the powerhouse of the cell. It produces ATP - the energy for the cell.
The smooth endoplasmic reticulum
The smooth endoplasmic reticulum produces fats and steroid hormones. It appears to be smooth, as it doesn’t contain any ribosomes.
Ribosomes
The ribosomes make protein. They can be attached to the rough endoplasmic reticulum or they can be free-floating in the cell.
The rough endoplasmic reticulum
The rough endoplasmic reticulum is involved with protein production. It folds, runs quality-control and dispatch with the proteins. It appears to be rough as it studded with ribosomes.
The Golgi Apparatus
The Golgi Apparatus modifies, sorts, and packages the proteins ready for secretion.
The peroxisomes
The peroxisomes break down fatty acids.
The secretory vesicles
The secretory vesicles store molecules and proteins produced by the endoplasmic reticula and Golgi apparatus, until they’re ready to be released by the cell.
The lysosomes
The lysosomes are involved in digestion and waste removal.
The centrioles
The centrioles help with cell division
The microtubules
The microtubules are part of the cytoskeleton; they play a structural role in maintaining cell shape. They also act like a conveyor belt inside the cell transporting organelles, vesicles, granules and chromosomes through the cell.
The nucleus
The nucleus is the control center of the cell. It contains the DNA, or genetic material that codes for every protein that the cell produces.
Protein synthesis
Protein synthesis begins with nucleic acids. Nucleic acids are long chains of nucleotides.
There are two types of nucleic acids; deoxyribonucleic acid, or DNA, and ribonucleic acid, or RNA.
DNA is a genetic code and it is the recipe for every protein we make. RNA is the template produced from DNA that is read by the ribosomes so that they can add the appropriate amino acids to the protein chain. RNA comes from DNA in a process called transcription (in the nucleus), and proteins are produced from RNA template in a process called translation, which occurs on ribosomes. From here proteins are either released into the cytosol, or go through the rough endoplasmic reticulum and Golgi apparatus for processing, packaging, and dispatch.
deoxyribonucleic acid, or DNA
DNA is the recipe for who we are, our characteristics, things like hair colour, eye colour, height, organ function, cellular function, and essentially everything about us comes from our DNA sequence.
DNA has two strands of nucleotide molecules arranged in a helix structure. The nucleotides, or phosphate sugars, in DNA are adenine, or A, cytosine, or C, guanine, G, and thymine, T. Every protein in our body is coded for by DNA.
Genes are sections of DNA strands that specify the amino acids that are required to make a specific protein. Each gene has multiple forms, or versions. These are called alleles and are inherited from your parents. The version you get is what makes you look and work the way you do. Variations in alleles contribute to individuality, which means that people and animals are never 100% identical.
ribonucleic acid, or RNA
RNA is the template that is produced from DNA to inform the ribosomes which amino acids to add to the polypeptide chain of the protein. RNA is a chain of nucleotide molecules but it consists of only one strand, not two like DNA. It uses the same nucleotides with the exception of thymine, which is replaced by uracil, or U.
Mitosis (cell division)
The cell cycle, or cell division cycle, is the sequence of events that takes place in a cell leading to its division; a copying of its DNA, or DNA replication, in order to produce two daughter cells.
Cells that continually wear away, such as those of the skin and in the intestine, are continuously dividing to replace themselves.
Other cells stop dividing once mature, but retain the capacity to divide rapidly if the organ or tissue becomes damaged, such as the liver.
There are cells that once mature, no longer have the capacity to divide, such as nervous tissue, skeletal muscle, and cardiac muscle. Damage to these cells, is replaced by fibrosis, or scar tissue.
Cell cycle phases
The cell cycle is the sequence of events that takes place in a cell leading to its DNA replication and division to produce two daughter cells. Most of the cell cycle consists of interphase where the cell replicates DNA and organelles ready to divide.
The mitotic phase occurs once all the preparations are complete, and during this phase the cell divides in two, producing two daughter cells.
Interphase
Interphase is the period from the formation of the cell, until it starts dividing, and includes G1 or Gap 1, a growth phase, ‘S’ the synthesis phase, where DNA is replicated, and G2 or Gap 2 where growth and final preparation for division occur.
Interphase refers to all stages of the cell cycle, other than mitosis. During interphase, cellular organelles double in number, the DNA replicates, and protein synthesis occurs. The chromosomes are not visible and the DNA appears as uncoiled chromatin. This is how cells look most of the time.
The miotic phase
The mitotic phase is the period where cells are actively splitting the replicated DNA and organelles, into two new cells. Cells that permanently cease dividing are said to be in G0 or Gap zero. Cells that remain in this phase, include neurons, skeletal muscle, and cardiac muscle.
Subphases include:
Prophase
prometaphase
metaphase
anaphase
telophase
Prophase
The first sub phase of the mitotic phase in the cell cycle, is prophase, where chromosomes become condensed and take on their traditional X configuration, and the nucleolus disappears.
Chromatin condenses into chromosomes and centrioles move towards opposite poles of cell.
Prometaphase
The centrioles move to opposite ends of the nucleus, and a mitotic spindle begins to form, during prometaphase, an intermediate step between prophase and metaphase, the nuclear envelope disappears.
Metaphase
Chromosomes line up along the metaphase plate, or the equator of the spindle, which is an imaginary plane.
Chromatids move to central zone.
Anaphase
The chromosomes separate and move towards the poles of the cell.
Centromere of each chromatid pair splits and chromatids separate.
Telophase
The chromosomes have reached opposite poles of the cell, and the nuclear envelope begins to form around them. The nucleoli start to reappear at this point, and the spindle breaks down and disappears. For a very short time the cell is actually binuclear or has two nuclei.
Cytokinesis
Cytokinesis is the term used to describe the cytoplasm dividing in two, which usually occurs immediately following telophase. Once complete there are two identical daughter cells which have originated from the original cell.
Membrane transport
Both nutrients ,and waste products from the cell, need to be transported across the plasma membrane. The plasma membrane is therefore selectively permeable as it allows the passage of some substances, but prevents the passage of other substances.
Transport, or movement of substances across the plasma membrane, can be either passive or active.
Passive transport
Passive transport does not require any energy expenditure.
Diffusion is a type of passive transport therefore no energy is required for this to occur.
There is a net movement of a substance down a concentration gradient, meaning from an area of higher concentration, to an area of lower concentration. An example of this is gas exchange with oxygen and carbon dioxide. There are a number of mechanisms by which this occurs, as not all substances can pass through a lipid membrane. These are:
-simple diffusion
-carrier mediated facilitated diffusion
-channel mediated facilitated diffusion
-osmosis.
Active transport
Active transport requires the cell to use ATP, or cellular energy for transport to occur.
Types of active transport include:
-Primary active transport
-secondary active transport
Transport can also be vesicular: endocytosis or exocytosis
Simple diffusion
In simple diffusion, nonpolar and lipid soluble plasma membrane are compatible substances, and able to diffuse directly across the plasma membrane. Substances able to move across the plasma membrane this way, include oxygen, carbon dioxide, and soluble vitamins.
Substances moved down a concentration gradient, for example oxygen concentration is high in the blood in the capillaries and low in the cells, therefore oxygen will move into the cells from the blood by simple diffusion, moving from the area of higher concentration, to the area of lower concentration.
Carrier mediated facilitated diffusion
Carrier mediated facilitated diffusion refers to specific ions or molecules being carried across the plasma membrane by integral proteins in the plasma membrane.
This occurs when the substance to be transported is water-soluble and is not compatible with the lipid structure of the plasma membrane.
These integral proteins are called carriers and when specific molecules bind the carrier changes shape, allowing the molecules to be encased by the carrier, then released on the other side of the membrane.
This type of transport is still passive, as substances are still moving down a concentration gradient. The difference is, they require an aqueous environment to cross through.
One example of this type of membrane transport are glucose transporters. The movement does not require energy as the glucose is moving down a concentration gradient.
Channel mediated facilitated diffusion
Channels are transmembrane proteins, able to transport substances through an aqueous, or water-soluble, environment across a membrane. These channels are selective for size and charge.
Leakage channels are always open, and allow molecules to move across concentration gradients.
Gated channels are controlled by signals; these can be
Chemical signals - through ligand gated channels that require a specific chemical to bind to the receptor to open the channel,
Mechanical signals - through mechanically gated channels that require pressure or other mechanical force to open the channel, or
Electrical signals, through voltage-gated channels that require a change in membrane potential to open the channel.
Osmosis
Osmosis is the diffusion of a solvent, as opposed to a molecule through a selectively permeable membrane. Solvents such as water, move from areas of low molecule concentration, or high amount of solvent, to areas of high molecule concentration, or low amount of solvent.
Primary active transport
Active transport requires ATP to provide energy, to move substances or molecules across a membrane. As energy is used, substances can be moved irrespective of the intracellular and extracellular concentration of the substance.
An example of this is the sodium potassium pump. Intracellular sodium is exchanged for extracellular potassium, and ATP is required for this process.
Secondary active transport
Secondary active transport is a consequent mechanism following primary active transport. Secondary active transport involves the movement of ions down a concentration gradient that has actually been created by the primary and active transport mechanism. This process allows for the cotransport of other charged molecules, either in the same direction ‘Symport’ or the opposite direction ‘Antiport’.
Endocytosis (vesicular)
Endocytosis is the process of transporting substances from the extracellular fluid to inside the cell. Vesicles generally form at the plasma membrane and bring fluids or solids into the cell.
Exocytosis (vesicular)
Exocytosis is the functional opposite of endocytosis. During exocytosis vesicles form inside the cell, and contain substances to be released. The vesicles fuse with and become part of the plasma membrane. The contents are then released into the extracellular fluid.
Tissues
Tissues are specialised groups of cells working together to perform specific functions. The study of tissue is called histology.
four primary tissue types; epithelial
connective
muscle
neural tissue
Epithelial tissue
Epithelial tissue usually covers exposed surfaces. The function of epithelial tissue is dictated by the shape and number of cell layers.
First part of name is number of layers. Simple refers to one single layer. Stratified refers to multiple layers of cells.
Second part of name refers to cell shape.
-Squamous are thin and flat.
-Cuboidal are short square shaped.
-Columnar are tall thin cells.
Are avascular (contain no blood vessels), must receive nutrients through diffusion or absorption.
Capable of regenerating.
Simple squamous epithelium
Simple squamous epithelium usually has the function of creating a frictionless surface, or allowing diffusion or exchange. The single layer, and thin nature of the cells, makes it easy for substances to pass across the cell, and the smooth surface reduces friction. These cells can be found live in cavities, blood vessels, and at the gas exchange surface in the lungs.
Stratified squamous epithelium
Stratified squamous epithelium is usually found in areas where abrasion may occur. The multiple layers allow the top layer of cells to be removed, without any damage to underlying tissue. This type of epithelium can be found on the surface of the skin, and in the mouth.
Simple cuboidal epithelium
Simple cuboidal epithelium are usually found lining ducts and glands, and usually secrete or absorb substances.
Stratified cuboidal
Stratified cuboidal is rare; it can be found along ducts of sweat glands and mammary glands.
Simple columnar epithelium
Simple columnar epithelium is involved in secretion and absorption. These cells have enough space to store produced substances waiting for secretion, or absorbed substances.
Stratified columnar epithelium
Stratified columnar epithelium is rare. This is only found lining large ducts such as in the pancreas or saliva glands.
Pseudostratified columnar epithelium
Pseudostratified columnar epithelium lines the respiratory tract. It looks like multiple layers of cells, but every cell is actually in contact with the basement membrane.
Transitional epithelium
Transitional epithelium has the ability to stretch and recoil. It is found lining the bladder. As the bladder fills with urine, the transitional epithelial cells flatten. When empty the cells return to their original shape.
Connective tissue
Connective tissue usually fills internal spaces and provide structural support for other tissues. It is also able to transport materials within the body, and is able to store energy.
Most connective tissues consist of specialised cells, as well as extracellular protein fibres, such as collagen fibres, reticular fibres, or elastic fibres, and ground substance or fluid which makes up the matrix. Connective tissue can be divided into different classifications.
The first type is connective tissue proper. This type can be described as either loose, or dense.
Loose connective tissue proper has an open mesh type of structure, and includes adipose tissue, which stores fat.
Dense connective tissue proper has a more condensed structure, and includes ligaments.
Fluid connective tissue includes blood and lymph.
Supporting connective tissue includes bone and cartilage.
Muscle tissue
Muscle tissue can be skeletal, cardiac, or smooth.
Skeletal muscle is involved in voluntary contraction, and is associated with movement.
Cardiac muscle is located in the heart, and provides the contractility of the walls of the heart.
Smooth muscle is usually incorporated into the walls of organs, and the involuntary contraction is generally associated with the organ function, or regulating the organ.
Neural tissue
Neural tissue is specialised to carry electrical impulses, from one part of the body to another. This tissue is specific to the nervous system.
