Molecular Biology
Introduction: An Overview
What is Molecular Biology?
Molecular Biology the study of biology at the molecular level.
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Focuses on the properties of individual molecules (nucleic acids & proteins) to explain the structure and function of cells & organism.
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Cellular processes​ regarding cell division & genomic information (DNA/RNA)
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Molecular Diagnostics is the application of molecular concepts via molecular technology to help health providers diagnose & treat diseases.
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>$3 billion market.
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Rapidly growing industry at >20% annually

The Human Genome Project
Basic Concepts
Hierarchy of Biological Organization

Small Molecule

Genes


Organ
Organ Systems




Protein
Organelle
Cell
Tissues

Organism

Replication
Transcription
Translation
Reverse Transcription
RNA
Replication
An Irreversible Process
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Protein can't be processed back into DNA
The "Central Dogma"
General:
This process happens for most cells
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DNA Replication (repeat as needed)
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Transcription: DNA to mRNA
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Translation: mRNA translated to synthsize protein
Special:
This process only happens for viruses & under specific conditions in the laboratory
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RNA Replication: RNA being copied from RNA
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Reverse Transcription
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Protein Synthesis
Vocabulary
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DNA- complete blueprint; stores all the genetic info needed to replicate cells
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RNA- partial copies of the blueprint that is needed to create specific proteins
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Protein- the end-product of the "Central Dogma"
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Structural cell component (part of the cytoskeleton
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Enzymes (help create everything in the cell)
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Major Cellular Processes
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Mitosis- process of cell division
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DNA Replication- to create another copy of DNA
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DNA Repair- mistakes in the copies need to be fixed
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Transcription- DNA being transcribed into RNA
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Translation- Proteins are synthesized from
Prokaryotic vs Eukaryotic Cells


Prokaryotes
Free-living unicellular organisms that lack a nucleus:
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"pro"- before
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"karyon"- nucleus
Characteristics:
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Nucleoid has DNA- no nuclear membrane
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Some has plasmid- single circular chromosome
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Simple organization without any membrane- bound organelles
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Has Cell (plasma) membrane
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Most have rigid cell wall
Eukaryotes
Single-celled or multicellular organisms with cells that contain complex, membrane-bound organelles
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"eu" - true
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"karyon"- nucleus
Characteristics:
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Double-membraned nucleus has DNA​
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Nucleoplasm- fluid suspending chromosomes & nucleolus inside nucleus
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No plasmid
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Complex organization with membran-bound organelles
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Has cell (plasma) membrane
Prokaryotic Vocabulary
Nucleoid
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Where bacterial DNA is located
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Not membrane-bound


Plasmid
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Single circular chromosome
Eukaryotic & Prokaryotic Cells
Ribosomes
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large proteins/ rRNA complexes found in both eukaryotic & prokaryotic cells
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site of protein synthesis
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can be free or attached to rough endoplasmic reticulum
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made of 2 subunits that combine only in the presence of:
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mRNA​
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appropriatly charged transfer RNA (tRNA
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Plasma/ Cell Membrane

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Phospholipid bilayer with associated proteins
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Boundary of the cells- provides functional separation between the inside of the cell & the outside environment
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Selectively allows O2, CO2, & H2O to diffuse​
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Impermeable to most molecules such as sugars, amino acids, Potassium, Chloride & Sodium ions which enter the cell through channels or transport proteins
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Contains many proteins which are involved in inter & intracellular communications
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Cell Wall
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Surrounds the cells of plants, many protists, fungi, archaea, and bacteria​

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Cell walls in different kingdoms differ in their chemistry
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Functions as protection as they provide rigidity to the cell
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Plants derive much of their support from the pressure of their fluid contents against the cell wall​
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Most prokaryotes have rigid cell walls made of polysaccharides​
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Protect cell from mechanical injury​
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Prevent bursting in osmoticaly unbalanced situations
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Cytosol
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Fluid component of the cell cytoplasm, not contained in membrane- bound organelles
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Consists of cytoskeletal elements such as microfilaments & microtubules​
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Cytoskeletal fibers provide strength & rigidity
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Helps control cell movement & chromosomal movement during cell division
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Site of Ttranscription & translation in prokaryotes
Eukaryotic Vocabulary
Nucleus
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largest organelle
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surrounded by double membrane nuclear envelope
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contains most of the cellular DNA
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site of cellular RNA synthesis

Nucleolus
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small spherical core inside the nucleus
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contains ribosomal RNA (rRNA) & many copies of the genes that encode rRNA
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site of rRNA transcription & assembly of ribosomal subunits

Mitochondria
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"Powerhouse of the Cell"
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located in cytoplasm
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bound by double membrane
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Endosymbiosis Theory- mitochondria evolved from symbiotic relationship between bacteria & eukaryotic cell creating double membrane
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Mitochondria also has their own DNA (independent genome and replicate by dividing in two​
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contains enzymes that drive the:
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citric acid cycle​
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the respiratory chain
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oxidative phosphorylation
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Oxidation of fatty acids & glucose make cellular ATP (energy)​
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Rough Endoplasmic Reticulum
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a network of membranes where proteins & glycoproteins are made​​​
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external surfaces are studded with ribosomes
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Smooth Endoplasmic Reticulum
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a network of membranes with no ribosomes
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site of lipid synthesis

Vesicle
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small membrane-bound sacs
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Spherical in shape
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Function in transportation in and out of cell

Lysosome
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bound by a single membrane & contain hydrolytic enzymes
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internal pH of the lysosome is acidic: pH 4-5

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Collaborates with vesicle formed by endocytosis & phagocytosis to digest material imported from the environment
Golgi Apparatus/ Bodies
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Packaging & processing station for the cell
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Folded membranes are arranged like stacks​

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Involved in the sorting of proteins & lipids destined for other cellular compartments or secretion
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Proteins are transported from the rough ER to the Golgi in small membrane vesicles
Vacuole
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Storage compartment found in some eukaryotes (plants)
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Functions as storage for:
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Water​
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Ions
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Waste Products
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Sucrose
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Nitrogen- containing compounds
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Genomic Structure
Cistron: old name for a gene
Poly-: more than one
Mono-: one
Prokaryotic Genome Structure
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Singular circular chromosomes (plasmid)
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1 origin of replication
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Polycistronic genes:
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mRNA carries the info of several genes, which are translated into several proteins​
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Coupled transcription/translation​

Eukaryotic Genome Structure
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Multiple linear chromosomes
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Multiple origins of replication per chromosome
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Interrupted coding sequences:​
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Introns & exons​
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Monocistronic genes:
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One gene contains the genetic information to translate only a single protein​
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Spacially separated transcription & translation


Virus
Simple intracellular parasites that cannot replicate on their own
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Consist of either a DNA or RNA genome
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Capsid: protein coat that surrounds the virus
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May have a lipid envelope that surrounds the capsid
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Viral Genomic Structure
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Virus replication depends on host cell metabolism​
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Bacteriophage- viruses that infect bacteria
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DNA viruses
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Can directly integrate into the host genome
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RNA viruses
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First make cDNA
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​cDNA or complementary DNA: ​DNA copy of the RNA strand​d
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Reverse Transcriptase: an enzyme has the ability to make a DNA copy of RNA
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Simple Virus

Bacteriophage
Sources
Zhang, J. (2020). CLLS3307: Molecular Biology, week 1 [PowerPoint slides].