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Molecular Biology

Introduction: An Overview

What is Molecular Biology?

Molecular Biology the study of biology at the molecular level.

  • Focuses on the properties of individual molecules (nucleic acids & proteins) to explain the structure and function of cells & organism.

    • Cellular processes​ regarding cell division & genomic information (DNA/RNA)

​

Molecular Diagnostics  is the application of molecular concepts via molecular technology to help health providers diagnose & treat diseases.

  • >$3 billion market.

  • Rapidly growing industry at >20% annually 

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The Human Genome Project

Basic Concepts
Hierarchy of Biological Organization
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Small Molecule

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Genes

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Organ 

Organ Systems 

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Protein

Organelle

Cell 

Tissues 

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Organism 

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Replication

Transcription

Translation

Reverse Transcription

RNA

Replication

An Irreversible Process

  • Protein can't be processed back into DNA

The "Central Dogma"

General:

This process happens for most cells

  1. DNA  Replication (repeat as needed)

  2. Transcription: DNA to mRNA

  3. Translation: mRNA translated to synthsize protein

Special:

This process only happens for viruses & under specific conditions in the laboratory

  1. RNA Replication: RNA being copied from RNA

  2. Reverse Transcription

  3. Protein Synthesis

Vocabulary

  • DNA- complete blueprint; stores all the genetic info needed to replicate cells

  • RNA- partial copies of the blueprint that is needed to create specific proteins

  • Protein- the end-product of the "Central Dogma"

    • Structural cell component (part of the cytoskeleton

    • Enzymes (help create everything in the cell) 

Major Cellular Processes

  • Mitosis- process of cell division

  • DNA Replication- to create another copy of DNA

  • DNA Repair- mistakes in the copies need to be fixed

  • Transcription- DNA being transcribed into RNA

  • Translation- Proteins are synthesized from

Prokaryotic vs Eukaryotic Cells
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Prokaryotes

Free-living unicellular organisms that lack a nucleus:

  • "pro"- before

  • "karyon"- nucleus

Characteristics:

  • Nucleoid has DNA- no nuclear membrane

  • Some has plasmid- single circular chromosome

  • Simple organization without any membrane- bound organelles

  • Has Cell (plasma) membrane

  • Most have rigid cell wall

Eukaryotes

Single-celled or multicellular organisms with cells that contain complex, membrane-bound organelles

  • "eu" - true

  • "karyon"- nucleus 

Characteristics:

  • Double-membraned nucleus has DNA​

    • Nucleoplasm- fluid suspending chromosomes & nucleolus inside nucleus

  • No plasmid

  • Complex organization with membran-bound organelles

  • Has cell (plasma) membrane

Prokaryotic Vocabulary

Nucleoid

  • Where bacterial DNA is located

  • Not membrane-bound

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Plasmid

  • Single circular chromosome

Eukaryotic & Prokaryotic Cells

Ribosomes

  • large proteins/ rRNA complexes found in both eukaryotic & prokaryotic cells

  • site of protein synthesis

  • can be free or attached to rough endoplasmic reticulum

  • made of 2 subunits that combine only in the presence of:  

    • mRNA​

    • appropriatly charged transfer RNA (tRNA

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Plasma/ Cell  Membrane

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  • Phospholipid bilayer with associated proteins 

  • Boundary of the cells- provides functional separation between the inside of the cell & the outside environment

    • Selectively allows O2, CO2, & H2O to diffuse​

    • Impermeable to most molecules such as sugars, amino acids, Potassium, Chloride & Sodium ions which enter the cell through channels or transport proteins

    • Contains many proteins which are involved in inter & intracellular communications

Cell Wall

  • Surrounds the cells of plants, many protists, fungi, archaea, and bacteria​

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  • Cell walls in different kingdoms differ in their chemistry

  • Functions as protection as they provide rigidity to the cell

    • Plants derive much of their support from the pressure of their fluid contents against the cell wall​

    • Most prokaryotes have rigid cell walls made of polysaccharides​

      • Protect cell from mechanical injury​

      • Prevent bursting in osmoticaly unbalanced situations

Cytosol

  • Fluid component of the cell cytoplasm, not contained in membrane- bound organelles

    • Consists of cytoskeletal elements such as microfilaments & microtubules​

    • Cytoskeletal fibers provide strength & rigidity

      • Helps control cell movement & chromosomal movement during cell division

  • Site of Ttranscription & translation in prokaryotes

Eukaryotic Vocabulary

Nucleus

  • largest organelle

  • surrounded by double membrane nuclear envelope

  • contains most of the cellular DNA

  • site of cellular RNA synthesis 

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Nucleolus

  • small spherical core inside the nucleus

  • contains ribosomal RNA  (rRNA) & many copies of the genes that encode rRNA

  • site of rRNA transcription & assembly of ribosomal subunits

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Mitochondria

  • "Powerhouse of the Cell"

  • located in cytoplasm

  • bound by double membrane

    • Endosymbiosis Theory-  mitochondria evolved from symbiotic relationship between bacteria & eukaryotic cell creating double membrane

      • Mitochondria also has their own DNA (independent genome and replicate by dividing in two​

  • contains enzymes that drive the:

    • citric acid cycle​

    • the respiratory chain

    • oxidative phosphorylation

      • Oxidation of fatty acids & glucose make cellular ATP (energy)​

Rough Endoplasmic Reticulum

  • a network of membranes where proteins & glycoproteins are made​​​ 

    • external surfaces are studded with ribosomes

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Smooth Endoplasmic Reticulum

  • a network of membranes with no ribosomes

  • site of lipid synthesis

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Vesicle

  • small membrane-bound sacs

  • Spherical in shape

  • Function in transportation in and out of cell

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Lysosome

  • bound by a single membrane & contain hydrolytic enzymes

  • 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

  • Packaging & processing station for the cell

  • Folded membranes are arranged like stacks​

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  • Involved in the sorting of proteins & lipids destined for other cellular compartments or secretion

  • Proteins are transported from the rough ER to the Golgi in small membrane vesicles

Vacuole

  • Storage compartment found in some eukaryotes (plants)

  • Functions as storage for:

    • Water​

    • Ions

    • Waste Products

    • Sucrose

    • Nitrogen- containing compounds

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Genomic Structure

Cistron: old name for a gene

Poly-: more than one

Mono-: one

Prokaryotic Genome Structure

  • Singular circular chromosomes (plasmid)

  • 1 origin of replication

  • Polycistronic genes:

    • mRNA carries the info of several genes, which are translated into several proteins​

  • Coupled transcription/translation​

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Eukaryotic Genome Structure

  • Multiple linear chromosomes

  • Multiple origins of replication per chromosome

    • Interrupted coding sequences:​

      • Introns & exons​

  • Monocistronic genes:

    • One gene contains the genetic information to translate only a single protein​

  • Spacially separated transcription & translation

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Virus

Simple intracellular parasites that cannot replicate on their own

  • Consist of either a DNA or RNA genome

  • Capsid: protein coat that surrounds the virus

    • May have a lipid envelope that surrounds the capsid

Viral Genomic Structure

  • Virus replication depends on host cell metabolism​

  • Bacteriophage- viruses that infect bacteria

  • DNA viruses

    • Can directly integrate into the host genome

  • RNA viruses 

    • First make cDNA

      • ​cDNA or complementary DNA: ​DNA copy of the RNA strand​d

      • Reverse Transcriptase: an enzyme has the ability to make a DNA copy of RNA

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Simple Virus

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Bacteriophage

Sources

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

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