Bio NOTES: Protein Synthesis

Protein Synthesis occurs in 2 parts: • part I - transcription• part II - translation

• the sequence of nucleotides in DNA codes for proteins

• proteins are very important for all life’s functions

Remember…

• DNA contains the instructions for making proteins

DNA makes proteins through a process called protein synthesis, which occurs in the ribosome.

DNA can’t do it alone so it gets help from another

nucleic acid - RNA.

Types of RNA• mRNA – messenger RNA

• tRNA – transfer RNA

• rRNA – ribosomal RNA

takes DNA information from nucleus to the ribosome

transfers or transports amino acids to the ribosome

used in making ribosomes

What is RNA?• RNA stands for ribonucleic acid• It is made of ribose sugars, phosphates, and nitrogen bases

• There is NO thymine in RNA – only adenine, cytosine, guanine and uracil

- uracil takes the place of thymine

A pairs with U C pairs with G

• RNA is single-stranded

Part I: Transcription

• occurs in the nucleustranscription = process where DNA is copied into mRNA

DNA cannot leave the nucleus but the message of DNA needsto get out of the nucleus

mRNA can take message of DNA out of the nucleus

1. DNA unzips2. mRNA bases pair with one of the DNA strands3. a single-stranded mRNA is made4. mRNA leaves the nucleus5. DNA zips back up

Steps of Transcription:

What is the message of DNA?? the order of nucleotides that determine a specific protein

Part I: TranscriptionA

T

G

G

C

A

DNA mRNAU

A

C

C

G

U

triplet codontriplet = 3 nucleotides on a DNA molecule

codon = 3 nucleotides on an mRNA molecule

DNA (triplets)mRNA (codons)

ATT CCT GAG TTC

UAA GGA CUC AAG

Each codon codes for a specific amino acid. The sequence ofamino acids determines the type of protein to be made. Remember that amino acids are the monomers of proteins.

All organisms use the same genetic code for amino acids andassembling proteins. That is why the genetic code is said tobe universal. mRNA codon: UUG

amino acid: leucine*See Genetic Code*

The Genetic Code

1. UUC

2. CCCProline

Phenylalanine

3. AGCSerine

4. UGAStop

Part II: Translation

• occurs in the ribosomes of the cytoplasm

1. The mRNA strand attaches to a ribosome in the cytoplasm2. tRNAs carry specific amino acids to the ribosome3. The tRNA anticodon pairs with the correct mRNA codon4. The ribosome slides along the mRNA to the next codon while the tRNAs bring more amino acids5. The amino acids are joined together by peptide bonds6. Continues until a STOP codon is reached

translation = process where the cell uses information from mRNA to produce proteins

Steps of Translation:

Part II: Translation mRNA

A

U

G

C

G

U

codonU

A

C

tRNA

Startcodon = 3 nucleotides on an mRNA molecule

anticodon = 3 nucleotides on a tRNA molecule

anticodon

tRNA is responsible for bringing amino acids to theribosome. tRNA has an anticodon, which is the opposite ofthe mRNA codon.It is important to remember that the mRNA codon determines the amino acid, NOT the tRNA anticodon.

mRNA:

tRNA:aminoacid:

U U A C G A A G C U C G

A A U G C U U C G A G C

Leucine - Arginine - Serine - Serine

DNA:

mRNA:

tRNA:

amino acids:

TAC AAG CTT GGG ATA CGC TAA ATT

UUC GAA CCC UAU GCG AUU UAA

AAG CUU GGG AUA CGC UAA AUU

Phenylalanine - Glutamic Acid - Proline - Tyrosine - Alanine - Isoleucine - Stop

**Remember – use the mRNA codons to determine the amino acids!!

Complete the Following Chart:

AUG

UAC

Start -