molecular genetics - grace mariniello

DNA —-> RNA —-> Proteins

(transcribing) (translating) 

NUCLEUS RIBOSOME


THREE TYPES OF RNA 


  • mRNA; messenger RNA = uses template to create a strand of corresponding base pairs, acting as instructions to the synthesis of proteins

  • tRNA; transfer RNA = brings the corresponding amino acid to the mRNA, this chain will turn into the primary structure of the final protein

  • rRNA; ribosomal RNA = RNA inside the core of the ribosome that helps structure, this type does not code


The Central Dogma; DNA to RNA to PROTEINS


TRANSCRIPTION


  1. DNA double helix

    1. DNA contains a gene; strand of nucleotides acting as a region for transcription 

    2. Begins with a promoter and ends with a terminator; the starting codon and the stop codon 

  2. RNA polymerase

    1. The RNA polymerase binds to the promoter (a transcription factor and recognition site)

  3. Elongation occurs

    1. The DNA double helix unwinds and mRNA is is made from the template strand in a 5’ to 3’ order

  4. Intron splicing

    1. Exons which code fo the protein are kept, introns are removed along with modifications adding a 5’ cap and a 3’ poly-A-tail

    2. Moved by a complex of proteins and RNA called a spliceosome

  5. Exits through a nuclear pore

    1. Once a mature mRNA is created


TRANSLATION


  1. Ribosomal unit - INITIATION

    1. A site where tRNA uses the mRNA to find and bring the corresponding amino acid, in the large ribosomal subunit there is the E, P, or A sites

    2. 4 sides; the anticodon which reads the mRNA, two others, and then the side with the amino acid which is on the 3’ side, all have hydrogen bonding

  2. Amino Acid Bonding - ELONGATION

    1. The amino acids bond to the previous one until a full polypeptide is formed AKA the primary structure of a protein

  3. Stop Codon - TERMINATION

    1. The stop codons hydrolyzes the bond between tRNA and the subunit, allowing them to dissociate


MUTATIONS


  1. Point mutations - base substitutions

    1. Only one real effect which is one amino acid change

      1. Missense Point Mutations

        1. Changes one nitrogen base causing an amino acid to change

          1. Transversion mutation is when one purine (A, G) is swapped for a pyrimidine (C, T)

          2. Transition mutation is when one purine or pyrimidine is swapped with the other (A to G and C to T)

      2. Silent Point Mutation

        1. Changes one nitrogen base that ends up not affecting the amino

      3. Nonsense Point Mutations

        1. Changes a base that instead codes for a STOP codon

 

  1. Frameshift mutations - inserts and deletions

    1. Normally fatal because they stop the protein from functioning due to the effect on the primary structure

      1. Deletions and insertions that are in groups of three or are divisible by 3 then it is not a frameshift

Mutations: 

  • Transition, Transversion, Insertion, Deletion

    • Sorted into point mutations, insertion, deletion

      • Results:

        • Missense, silent, nonsense, frameshift, insertion, or deletion.


GENE REGULATION


Operons - a process of regulating and maintaining the process of protein synthesis by allowing or not allowing the binding of RNA 


PARTS IN AN OPERON PROCESS >> (trp and lac or negative operons, positive use activator proteins; when activated then they attach they turn on the gene transcription. Not activated turns off the gene because the RNA polymerase can not bond)


  • DNA strand - strand where the person process takes place

  • Regulator gene - gene right before the promoter that codes for the repressor molecule

    • TWO MAIN FUNCTIONS

      • Turning the gene on and off

      • Recruiting enzymes to add and remove tags

  • Promoter - initiating region on the DNA strand where the RNA polymerase is able to bind

  • Operator - where the repressor molecule will bind to stop the transcribing 

  • Gene - the region on the DNA of transcribing

  • Repressor - molecule that binds to the operator to stop the process

  • RNA polymerase - binds to the promoter and reads the base sequence in 3’ to 5’ order


Repressible operons (TRP OPERONS) - produces enzyme that synthesizes tryptophan

  • When there is no trp present, the transcribing continue

  • When there is trp present, it binds to the repressor molecule, activating it by changing its shape when it binds. Allowing it to bind to the operator and stop transcription


>>WHEN TOO MUCH TRP IS BEING PRODUCED BY TRANSCRIBING IT IS TURNED OFF BY THE REPRESSOR<<


Inducible operons (LAC OPERONS) - produces enzymes that metabolize lactose

  • When there is no lac present, the repressor is active and bind to the operator, stopping the transcribing by RNA polymerase

  • When there is lac present it binds to the repressor which changes the shape, unbinding it from the operator and allowing transcribing


>>WHEN TOO MUCH LAC HAS ACCUMULATED IT TURNS ON TRANSCRIPTION TO METABOLIZE THE SURPLUS<<



Epigenetics


EPIGENOME - structure of DNA and histone covered in series of chemical tags

EPIGENETIC TAGS - “long term memory” help the gene stay on correct function

GENOME - an organism's complete set of DNA 

EPIGENETIC PROFILE - a collections of epigenetic tags that determine if the gene is off or on


  1. DNA wraps tightly around the protein histones

  2. Both these are covered in a series of chemical tags

    1. Called an epigenome

    2. Epigenome changes the physical structure of a genome

  3. Epigenetics pick up signals from the environment

    1. These signals are brought to the DNA by proteins

    2. Stress; Diet; Toxins: Physical Activity


  • DNA is fixed but the epigenome is flexible 


Tightly wrapped —> inactive gene and no reading

Relaxed unwrapped —> active and can be read easily


Experience can be passed on to the daughter cells

  • EPIGENETIC INHERITANCE 


  • Parents experience through life can be passed down through epigenetic tags

  • Although reprogramming occurs for the reproductive cells to meet and divide epigenetic codes can bypass both the egg and the sperm to avoid the reprogramming in early development


What con conflict with the idea of Epigenetic Inheritance


  • Genetic changes

    • In larger animals genetic changes or mutations would be hard to notice

  • Direct exposure

    • Inheritance must pass through multiple generations withouts direct exposure that can affect and influence