Cell Structures Unit B1 Analyse the functional interrelationships of cell structures
Students who have fully met the prescribed learning outcomes (PLO’s) are able to:
B1. Analyze the functional interrelationships of cell structures.
Describe the following cell structures and their functions:
mitochondria, cristae and matrix
nucleus, nuclear pore, nucleolus, chromatin, nuclear envelope, and chromosomes
smooth and rough endoplasmic reticulum
State the balanced chemical equation for cellular respiration.
C 6 H 12 O 6 (aq) + 6O 2 (g) -> 6CO 2 (g) + 6H 2 O (l)
Describe how the following organelles function to compartmentalize the cell and move materials through it:
-Rough and smooth endoplasmic reticulum
Identify cell structures depicted in diagrams and electron micrographs .
So lets begin…
The “gatekeeper” of the cell; Composed of a flexible phospholipid bilayer with protein molecules partially or entirely embedded; Carbohydrate chains (composed of C 6 H 12 O 6 ) attached to proteins and lipids on the outside of the membrane are called glycoproteins and glycolipids .
Functions: only 4 for now.
Separates contents of cell from environment.
Regulates entrance/exit of molecules via diffusion, osmosis, endocytosis, exocytosis, phagocytosis and/or pinocytosis.
Cell recognition of foreign cells and microorganisms by glycoproteins or glycolipids.
Compartmentalizes or divides cell to serve as partitions, or regions for specific reactions within the cell.
Function: provides support and rigidity
Found in plants and algae containing the pigment, chlorophyll
Contains its own DNA
Bound by a double phospholipid membrane; consists of flattened membranous sacs and fluid.
Site of photosynthesis
Converts sun energy into glucose
Cyto – Greek for “cell”
3-D network of protein fibres connected to most organelles
Actin (red) and Microtubules (green)
So what does the cytoskeleton do?
Provides framework within cytoplasm for organelle movement
Provides support for cell shape
Provides for movement of substances within cells
Also called: Cytosol
Well “plasm” means “fluid substance”
Compartments bounded by cell membrane
Contains: water, many organelles, dissolved gasses, ions, enzymes, proteins, nucleotides, amino acids, sugars, carbohydrates, organic molecules, etc.
Compartments allow metabolic reactions to occur and suspends organelles
Assists in the production and distribution of molecules via compartmentalization
Helps materials move around the cell by moving and churning through cytoplasmic streaming
The first phase of energy production (glycolysis) takes place here
Consists of 6 or more stacked, flattened membranous sacs called “saccules”.
One side faces the nucleus and the ER and the other side faces the cell membrane.
Small membranous sacs occur at edges called vesicles .
Modifies/process , packages , stores and distributes proteins produced by ribosomes on ER into vesicles to be exported or transported to other sites in the cell, e.g. hydrolytic enzymes (proteins) into lysosomes.
Golgi Bodies Function
Small membrane-enclosed sacs that are pinched off portions of membranes moving from the site of one membrane to another
(Note: the flexibility of the phospholipid bilayer allows for this to occur).
Cellular processes which make use of vesicles include the following:
autolysis, intracellular digestion, pinocytosis and phagocytosis, packaging of neurotransmitters and viruses, storage of Ca 2+ in muscle cells or macromolecules in liver & muscle cells and plant cells, production of cell products in the rER and sER, storage and modification of cell products from Golgi bodies, detoxification of alcohol and drugs into H 2 O-soluble products, and breaking down H 2 O 2 (hydrogen peroxide: a toxic byproduct made by many enzymes) into H 2 O + O 2 via the enzyme catal ase (i.e. in peroxisomes) located in the liver
Two types of vesicles
Membrane-bound sacs/vesicles contains products/molecules for secretion, e.g. proteins (enzymes, keratin, collagen, hemoglobin, membrane proteins etc.), enzymes (DNA/RNA polymerase, hydrolytic enzymes, amylase, pepsin, maltase, etc.), hormones (testosterone, estrogen, thyroxin etc.), phospholipids and steroids (sex hormones, aldosterone etc.) produced and released from ribosomes/rER and sER to the Golgi bodies.
Modified and repackaged proteins, steroids, hormones etc. from Golgi body are taken in secretory vesicles to the cell membrane for secretion via exocytosis .
Membrane-bound sacs/vesicles formed by Golgi apparatus, which contain hydrolytic enzymes .
Hydrolytic enzymes break down polymers into monomers/unit molecules
Destruction of cells by hydrolytic enzymes during development and metamorphosis, i.e. “suicide bags”.
Used for intracellular digestion of food-filled vesicles/vacuoles by hydrolytic enzymes into simple molecules/monomers, e.g. polypeptides into amino acids.
4 H 2 O + ○-○-○-○-○ + hydrolytic enzymes ○ ○ ○
Auto digestion of damaged/worn cell parts by hydrolytic enzymes for recycling, e.g. mitochondria, red blood cells etc.
A larger membrane-enclosed sac.
Storage of macromolecules such as a food vacuole formed by phagocytosis.
Storage of water and/or waste products.
The “ powerhouse ” of the cell
Membrane-bound organelle with its own DNA (deoxyribonucleic acid, i.e. mDNA (mitochondrial DNA)
Contains 2 membranes: an inner folded/convoluted membrane called cristae and a smooth outer membrane.
The matrix is the inner fluid-filled space containing DNA, RNA, ribosomes, proteins, enzymes, H+/protons etc. (Note: membranes are also composed of phospholipids and proteins)
Undergoes process of aerobic cellular respiration . See balanced chemical equation below. (Mitochondria are very active and numerous in muscle cells, cardiac cells, neuron cells, sperm cells and proximal and distal convoluted tubule cells of the nephron/kidney).
C 6 H 12 O 6 + 6O 2 6H 2 O + ATP + 6CO 2
Aerobic cellular respiration
C 6 H 12 O 6 + 6O 2 6H 2 O + ATP + 6CO 2
C 6 H 12 O 6 = glucose/carbohydrate
ATP = A denosine t ri p hosphate
The cells energy source for cellular activities such as: cellular respiration, DNA replication, protein synthesis, hydrolysis & dehydration syntheses, enzymatic reactions, active transport, endo/exocytosis, pino/phagocytosis, nerve transmission, Na+/K+ pumps, cellular detoxification, sperm motility, organelle movement, muscle contraction etc.
Cristae – the folds
increases surface area for cellular respiration and the production of ATP with the aid of several proteins and complexes (e.g. ATP complexes, transport proteins/electron transport chains).
Matrix – the space between the folds
Assists in the chemical production of ATP/the metabolic/oxidative breakdown of C 6 H 12 O 6 via several enzymes.
Contains mitochondrial DNA, RNA, ribosomes, proteins, enzymes etc. necessary for their own protein synthesis.
Enzymes = proteins that are required to catalyze/speed up the rate of reaction.
Large membrane-bound organelle consisting of two layers of phospholipids similar to the cell membrane; contains the chromatin/ chromosomes of the cell.
Stores genetic information as DNA (deoxyribonucleic acid).
Contains genetic information for making proteins.
Controls all cellular activities and protein synthesis
Nuclear envelope/membrane and nuclear pores
Double membrane consisting of phospholipids and many protein pores / nuclear pores surrounding the nucleus.
Forms a boundary separating contents of nucleus from cytoplasm.
Allows transfer of molecules between nucleolus and cytoplasm through the nuclear pores , e.g. nucleotides, mRNA, rRNA and proteins/enzymes.
Found within the nucleus; consists of 2 or more darker, spherical bodies in non-dividing cells.
Contains rRNA (ribosomal ribonucleic acid), proteins and ribosomal DNA.
Ribosome synthesis (produces rRNA which is a necessary subunit for the formation of ribosomes).
Chromatin are masses of fine fibres (long, double-stranded molecule of DNA and proteins) in the nucleus of a non-dividing cell.
Contains all the genetic information that condenses during cell division to make chromosomes.
Chromosomes are rod-like, coiled structures composed of chromatin fibres found within the nucleus .
Chromosomes remain condensed and visible in the nucleus just prior to cell division.
Humans have 46 chromosomes except in gamete cells.
Contains all the genetic information in triplet codes,
e.g. CAT GAG TCA.
Made of 2 sub-units, rRNA (ribosomal RNA) and proteins and therefore are not membrane-bound.
rRNA sub-unit is produced by the nucleolus.
They may be free, i.e. suspended in the cytoplasm or attached to the rough endoplasmic reticulum.
Site of protein synthesis . Produces secretory proteins or polypeptides, such as enzymes (as they are required for all chemical reactions), Hb, glycoproteins etc (See Unit B4).
1 = large sub-unit 2 = small sub-unit
A linear collection of several ribosomes attached to one mRNA.
Produces many copies of polypeptides (via protein synthesis) when attached to the mRNA, e.g. the protein pigment Hb (hemoglobin) is formed by polysomes.
Consists of tubular canals that attaches to the nuclear envelope and branch out throughout the cytoplasm thus increasing surface area. Most eukaryotic cells contain ER.
There are 2 types: smooth and rough
Smooth Endoplasmic Reticulum
Appears smooth because it lacks ribosomes.
Abundant in testes (interstitial cells), ovaries, adrenal glands and liver.
Synthesizes sex hormones (e.g. testosterone, estrogen)/steroids, aldosterone, membrane lipids (phospholipids, i.e. assembly of glycerol and fatty acids) and packages them into vesicles.
Detoxifies alcohol, drugs and poisons in the liver with the help of enzymes into H 2 O-soluble products.
Rough Endoplasmic Reticulum
Have ribosomes (produced by nucleolus) attached to an extensive membranous network of tubules and sacs.
Abundant in villi (small intestines) for the production of digestive enzymes, red bone marrow for RBC and WBC production etc.
Attached ribosomes produce proteins, which are then transported throughout the cell in tubules/canals to be exported out.
For some extra fun….
There are a few additional structures to know.
Cilia and Flagella
Cilia are short organelles and more numerous than flagella.
E.g. they line the nasal passageway and respiratory tract, sweeping the mucus & trapped foreign materials. In the fallopian tube, cilia help to sweep the egg along. (See C8 &15)
Flagella are long, hair like organelles which permit movement for sperm cells.
Cilia line the upper respiratory tract (400x)
Microscopic finger-like extensions of the cell membrane composed of cytoskeleton filaments.
To increase surface area for absorption and secretion of molecules and enzymatic activity. E.g. abundant in epithelial cells of intestinal villi, and proximal convoluted tubule cells of the nephron/kidney. (See C1 & 13)
Note: all the above structures require the use of ATP.
Time to get creative!!
How it works….
The cell is divided into several compartments containing organelles & enzymes. This increases the surface area for each compartment to perform specific functions and thus become specialized.
*-The following membrane-bound structures, nucleus / nuclear envelope , ER (rough and smooth), Golgi bodies , vesicles , vacuoles and lysosomes , have a functional interrelationship. They function together in the synthesis and transport of molecules within the cell or for export out of the cell. For example, the production, distribution and secretion of a protein such as enzymes, hemoglobin, keratin, collagen etc. See the following description and diagram:
1.) Nucleus contains genetic code for a protein.
2.) Ribosomes produce proteins (protein synthesis).
3.) Rough ER temporarily stores proteins or enzymes (made by ribosomes) in the tubules, travels through the ER, and pinches off to form vesicles .
4.) Vesicles migrate (assisted by microtubules/cytoskeleton ) to the Golgi bodies from the ER and the Golgi modifies and repackages proteins into another vesicle . Depending on the substances within the vesicle, it can be…….
5a.) Secretory vesicles containing secretory proteins are moved by microtubules/cytoskeleton to the cell membrane . Vesicles fuse with cell membrane and release the proteins through exocytosis OR,
b.) Lysosome vesicles containing hydrolytic enzymes (proteins) are retained in the cell to fuse with a food vacuole/vesicle (cell membrane folds in and around food/molecules producing a vacuole/vesicle through endocytosis ) and breaks down the macromolecules into smaller molecules, i.e. intracellular digestion .