From DNA to Protein

Bellringer 11/4/10

1. Based on the picture on the board, where does transcription occur?

2. Where does translation occur?

Section 2: Genes and Proteins• The sequence of nucleotides in DNA contain

information. This information is used to make proteins

• Proteins make cells and regulate their functions.• Proteins are made of subunits/monomers called

amino acids • The sequence of DNA nucleotides determine the

amino acids used to build proteins

RNA-Ribonucleic Acid• Full name: Ribonucleic Acid• In base pairing, thymine (T) is

replaced by uracil• Function: plays a role in making

proteins

• RNA Nucleotide Structure:1. Ribose (sugar)2. Phosphate3. Nitrogen bases

A pairs with U

C pairs with G

Types of RNA

• mRNA: messenger RNA; made from DNA & it carries DNA information from the nucleus to the cytoplasm

• rRNA: ribosomal RNA; combines with ribosomes to make proteins

• tRNA: transfer RNA; carries amino acids to the ribosomes

Comparing DNA and RNADNA RNA

Strands 2 1

Sugar Deoxyribose Ribose

Types of Bases/Base Pairs

A-TC-G

DNA – RNA RNA-RNA

A-U U-AC-G C-GSo why is RNA important? Because DNA is

too big to leave the nucleus and it uses RNA to take its message out into the cytoplasm.

Transcription • Location: Nucleus• Purpose: DNA information is

copied into mRNA. • Caused by RNA Polymerase

(an enzyme)

DNA is safe in the nucleus

Uses mRNA To send a message to the cytoplasm

FYI: How does this happen? – Unzip one gene in DNA – Match up bases to one side of

gene in DNA– A binds with U, C binds with G.– mRNA detaches from the DNA– mRNA moves out of the nucleus

and into the cytoplasm

• DNA: GAG AAC TAG TAC• RNA: CUC UUG AUC AUG

Translation • Location: Cytoplasm at the Ribosomes

• Purpose: tRNA matches to the mRNA to make a specific amino acid chain which is a protein.

How are the Nucleotides of Messenger RNA Translated into a Protein? Events of translation:1. The first three bases of mRNA (codon) join the

ribosome. Its usually AUG – considered the start codon).

2. tRNA brings the “amino acid” down to the ribosome. The three bases on tRNA (anticodon) match the complementary bases on mRNA.

3. Each tRNA has an amino acid, which is determined by its anticodon.Ex: codon (AUG) is for the amino acid - methionine

4. The amino acids are joined by polypeptide bonds.

5. The resulting chain of amino acids are called a PROTEIN.

Codons & Anticodons

• CODON: mRNA bases needed to call an amino acid to the ribosome

• Start codon: AUG and it codes for the amino acid methionine

• Stop codon: mRNA that means the end of the AA chain has been reached

• ANTICODON - segment of three bases on tRNA that is complementary to the mRNA codon.

Practice with Protein Synthesis

ProcessInformation for

processProduct

Type of Base Pairing

Required

Replication(synthesis of

DNA)

Entire length of double helix

DNA DNA with DNA

Transcription (synthesis of

RNA)

Small part of a DNA strand

mRNA DNA with RNA

Translation (synthesis of

protein)

mRNA Protein mRNA with tRNA

But What Happens When Any of These Processes Goes Wrong…

Mutations…

What is a mutation?• Any change in the DNA sequence

What is a mutagen?• Any agent that can cause a change in DNA

How can mutations happen? • Spontaneous mistakes in base pairings• radiation• chemicals• high temperatures

Types of Mutations

–Point Mutation: a change in a single base (like a substitution)

GAG CTC CUC Leucine

Correct DNA Correct mRNA Correct AA

GCG CTC CGC Arginine

A should pair with T, but instead C is mismatched to T

Point mutation mutated mRNA Wrong AA

Mutations

• Example: Sickle Cell Anemia

Frameshift mutation: when one or more

bases are added or deleted from DNA. Correct DNA: ATA CCG TGA TAT GGC ACT

Correct mRNA: UAU GGC ACU

Correct amino acids: Tyrosine Glycine Threonine

Extra inserted base SHIFTS how we read the codons (3 bases), which changes the amino acids

Frameshift mutation ATG ACC GTG Ain DNA: TAC TGG CAC T

Mutated mRNA: UAC UGG CAC U

Wrong amino acids: Tyrosine Tryptophan Histadine

Frameshift Mutations: Insertions

Frameshift Mutations: Deletions

Chromosomal Mutations

• Structural changes in chromosomes

• Caused by four types of mistakes

Insertion- When a part of a chromatid breaks off and is added to its sister chromatid so that the gene is duplicated

Deletion- When a part of a chromosome is left out

Translocation & InversionTranslocation: When a part of the chromosome breaks off and is added to a different chromosome

Inversion: When a part of the chromosome breaks off and is reattached backwards

Mutations

• Frameshift mutations can have catastrophic effects on genes because ALL the codons that follow the shift will be altered, not just one.

• Proofreading enzymes are able to repair some damages to DNA