Protein Synthesis, Mutations and Genetics Biology 30

What is Genetic Code?

The order if the base pairs in a DNA molecule makes up the genetic code of an organism

• The order of nucleotides in a gene provides the information, written in genetic code, that is necessary to build a protein

The way information in a gene is converted into a specific chromosome or trait is called Gene Expression

What is a Protein?

Long chain of amino acids (monomers)

Every protein has to be coded for in DNA

The function of a protein is dependent on its shape

• Uses: muscle, enzymes, hormones, cell membranes etc

The theory that information flows from DNA to RNA to protein is reffered to as “central dogma”

Protein = polypeptide (many amino acids)

What is Central Dogma?

Has 2 main stages: Transcription and Translation

During gene expression, DNA is copied into an RNA molecule (mRNA) in a process called transcription

The second step of gene expression is called translation

What is Gene expression?

Transcription:

• DNA is copied to a special type of RNA molecule calledd messenger RNA (mRNA)

• This happens in nucleus —> DNA doesnt leave nucleus

Translation:

• The mRNA migrates to the cytoplasm of the cell. Here the sequence of nucleotides on the mRNA molecule directs the synthesis of a polypeptide chain (string of amino acids) with the help of transfer RNA (bring amino acids) (tRNA) and ribosomal (rRNA)

  • Ribosomes are made up of ribosomal RNA

What is RNA?

Ribonucleic acid

Different sugar (ribose sugar —> 5 carbon sugar)

Single stranded

Thymine is replaced by uracil

• A pairs with U

• G pairs with C

What are the types of RNA?

mRNA: messenger —> takes code from nucleus to cytoplasm —> single stranded

tRNA: transfer —> carries specific amino acids to ribosome (rRNA) —> 20 different tRNA molecules each specific to the 20 amino acids)

mRNA codon: triplet of nucleic acids (nucleotides)

What are Codons and Anticodons?

Codon: a code of mRNA which is made up of 3 nitrogenous bases that code for a specific amino acid.

More than 1 codon can code for an amino acid, they serve as stop signals to end synthesis of a polypeptide

• 64 codons only 20 amino acids —> repeat some

  • Start codon: start synthesis of protein (AUG)

  • Stop codon: stop synthesis of protein (UAA, UAG, UGA)

What is RNA polymerase?

Binds to DNA and begins the transcription process. Many RNA polymerase can bond to multiple sites on the DNA at the same time for efficieny

What is the first step of Transcription?

Initiation: RNA polymerase (enzyme) binds to DNA at a specific site near the beginning of a gene

A sequence of nucleotides (sequence of A & T) acts as promoter side —> side that indicates to the RNA polymerase where to bind

• looks for this to know where to start

• Ex. TTATTAAATTAT

What is the second step of Transcription?

Elongation: RNA polymerase builds single stranded RNA In a 5’-3’ direction

• Transcribed DNA strand = template strand

• use 3’-5’ side of DNA. RNA runs 3’-5’ and new mRNA is built from 5’-3’

What is the third step of Transcription?

Termination: synthesis of mRNA continues until a terminaion sequence is reached the mRNA disconnects

• mRNA moves to the cytoplasm to start to make protein

What are Amino acids?

20 different amino acids make up proteins

Proteins can have various amounts of amino acids and the sequence of amino acids can vary

• shape determines function

What is Translation?

mRNA code is read in groups of 3 nucleotides = codon

• 4³ = 64 possibilites (4 bases)

• Start codon —> AUG (methianine)

• Stop codon —> UAA, UAG, UGA

  • Dont code for amino acids just signal to ribosome that its the end of protein

What is the first step of Translation?

Initiation:

• ribosome binds to mRNA

• 2 subunits clamp mRNA between it

• ribosome moves in 5’-3’ direction until it finds a start

What is the second step of Translation?

Elongation:

• tRNA with complementary start codon attaches to mRNA

• next in line enter the next site

• peptide bond forms between 2 amino acids

• ribosome shifts over 1 codon

What is the third step of Translation?

Termination:

• When a stop codon is reached, the ribosome mRNA complex breaks apart, releasing the polypeptide

• mRNA can be reused

What are the Nucleic Acids involved in Gene Expression?

DNA: double helix —> stores genetic information (how to code for protein)

mRNA (messenger): linear single strand —> carries genetic information from DNA to the protein synthesis equipment. IN eukaryotes, the mRNA is processed before it moves to the cytoplasm for translation (nucleus —> cytoplasm)

tRNA (transfer): lobed shaped —> carries a particular amino acid to the correct codon site in the protein synthesis equipment

rRNA (ribosomal): linear single strand —> combines with a complex of proteins to form a ribosome, the main structure of protein synthesis

What are mutations?

A permanent change in the genetic material of an organism

• All mutations are inheritable and are copied during DNA replication and passed on to daughter cells (when cells divide)

• Mutations are only passed on to offspring if the mutation affects the genetic information in the gametes

What are the 2 catergories of mutations?

Induced:caused by a mutagen

• chemical: pesticide etc

• physical: UV radiation, x rays etc

Spontaneous: DNA replicates and mistakes is made and NOT caught

• DNA polymerase misses mistakes

What are Somatic Cells and Gametes?

Somatic (Somatocytes) cell: any cell but gametes —> body cells

• If mutate, can NOT be passed onto offspring only passed to daughter cells from division

Gametes (germ cells): reproductive cells (egg/sperm cells)

• if mutate, CAN be passed onto offpsring

What are Missense Mutations?

Results in the single substitution of one amino aid in the polypeptide

• This substitution may lead to slightly altered by still functional protein

What are Nonsense mutations?

Renders the gene unable to code for a functional polypeptide

• converts a codon for an amino acid into stop codon

What are deletion mutations?

Elimination of a base pair or group of base pairs in a DNA sequence

• leads to frameshift

What are insertion mutations?

Placement of an extra nucleotide in DNA sequence

• lead to frameshift

What are frameshift mutationS?

Causes the reading frame of codons to change (insertion or deletion of any # but 3 nucleotides)

• if 3 added usually still functional

What are Translocation mutations?

Transfer of a fragment of DNA from one site in the genome to another location

• transfer location of genes (found in chromosome)

What are inversion mutations?

Reversal of a segment of DNA within a chromosome

What are substition?

One nitrogenous base is replaced with a different nitrogenous base

What are restriction endonucleus?

Restriction enzyme is an enzyme that cuts double stranded or single stranded DNA at a specific recognition nuceltoide sequence known as restriction sites

Occurs in viruses and bacteria

What is the importance of restriction endonucleuoses?

Valuble because any 2 fragments of DNA produced by the same restriction endonuceliasas can be joined together

Restriction endonucleases are fundamental in genetic engineering

Asexual reproduction: increases variation

How does restriction endonucleases work?

The target sequence of the restriction endonucleases is known as EcoR1 —> GAATTC

Wherever this sequence appears on one strand of DNA molecule, the same sequcen will apeear runnin gin opposite direction on complementary strand

The result is s set of fragments with exposed complemetary nucleotide sequences

These “sticky ends” may base pair with another trhough assistance of DNA ligase

• make phosphodiester bonds

• restriciton enzyme cuts

• DNA ligase glues

What is sorting and analyzing DNA?

Gel electrophoresis: is used to seperate molcuels accoridng to their mass and change

• it can be used to seperate fragments of DNA by creating a DNA fingerprint

What is recombinant DNA technology?

Is the process of transferring genes from one organism to another organism

thsi enables the "“genetically modifited organism” (GMO) to produce new proteins creating a desried effect

• restriction enxymes cut DNA —> glue DNA with ligase = recombinatn DNA technoloy

What is gene therapy?

Gene therapy is medical technology trhough which genes are inserted into a personas cells tp treat a genetic disorder. The genes act as medicine for the disorder

• not modifying just inserting and treating

The therapeutic genes are placed inside a virus that has been rendered harmless, and the viral capsule releases the genes into the cells of patient

Ex. person with hemophelia (no bloodclotting factors) get gene with factor injected with gene to make blood clotting factor

What are silent mutations?

Does not result in a change for the amino acid coded for

• has no effect on the cells metabolism (neutral mutation)