Protein Synthesis

Genes Proteins

Genes: a sequence of nucleotides in DNA that performs a specific function.Each gene contains the instructions to build a specific protein.It is the proteins that our bodies make that give us our traits – freckles, brown eyes, blond hair, etc.

Proteins

Proteins: complex molecules composed of amino acids. There are 20 different amino acids.Different combinations of these 20 amino acids create different proteins.Proteins are made outside the nucleus by organelles called ribosomes.

Remember…

Genes are located on chromosomes. Chromosomes are made up of coiled DNA. Therefore, genes are made up of sections of DNA. Genes contain the instructions to make specific proteins which give us our genetic traits.

???

Proteins are not made inside the nucleus, and DNA cannot exit the nucleus! So how can the instructions from the genes actually make proteins to give us our traits if they are in two places?!

This is where the process of Protein Synthesis comes in!

(without protein synthesis, our cells would not operate, genes would not be expressed, cells would die, etc.)

DNA, RNA, & ProteinsFor proteins to be created - it starts with the DNA. DNA strand is transcribed into a language that

is understood outside the nucleus. It is transcribed into “messenger RNA”.The mRNA strand is able to exit the nucleus,

carrying the instructions from the gene (DNA). Ribosomes translate the RNA code and begin

making the necessary proteins.

Transcription & TranslationTranscription: involves the copying of the information in DNA into messenger RNA. When you transcribe, you copy from one medium to

another. Translation: involves ribosomes using the messenger RNA as blueprint to synthesize a protein composed of amino acids.When you translate, you convert into a different

language.

The basics of protein synthesis

DNA is transcribed into complementary messenger RNA, and ribosomes translate messenger RNA into specific sequences of amino acids, which are used to build proteins!

Protein Synthesis – Two Stages(the details)

Protein Synthesis involves two main steps:TranscriptionTranslation

Step 1: TranscriptionOccurs in the nucleus and results in the formation of messenger RNA (mRNA)

1. Hydrogen bonds break and a portion of DNA unzips

2. RNA nucleotides form a complement to one side of the unzipped DNA

3. The RNA complement is called mRNA and it leaves the nucleus carrying a copy of a DNA gene.

4. The DNA zips back up, unchanged.

The Genetic CodeTo code for all amino acids, a sequence of three nucleotides must be used for each amino acid.Each triplet of nucleotides on RNA is referred to as a codon. One code serves as a start codon and others serve as stop codons.Refer to p. 240 in Nelson Biology 12 text for genetic code table

Universal Codes

The codons on the mRNA are universal. In other words, GGG codes for the amino acid glycine regardless of whether it is in a human, a dog, or a bacteria.

Transcription Animation

http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/translation.swf

Step 2: TranslationOccurs in the cytoplasm on the ribosomes.Transfer RNA (tRNA) are clover-leaf shaped molecules that carry 3 bases on one end, called an anti-codon, and a specific amino acid on the other end.

Step 2: Translation1. The ribosome moves along the mRNA

one codon at a time.2. The tRNA with the complementary

anti-codon temporarily bonds with the mRNA codon and brings its amino acid with it.

3. The ribosome moves to the next codon, the matching tRNA appears.

Step 2: Translation, cont’d

4. The amino acids bond to each other.5. This process continues until the

ribosome hits a “stop” codon.6. The amino acids that bonded to each

other result in a protein (polypeptide chain).

http://highered.mcgraw-hill.com/sites/0072943696/student_view0/chapter2/animation__protein_synthesis__quiz_1_.html

Translation Animation

Also see Figure 4, page 252 of Biology 12 Textbook

Interactive – Protein Synthesis!

http://learn.genetics.utah.edu/content/begin/dna/transcribe/

Complete the ‘TRY THIS Activity’ on page 233 of Biology 12 textbook. Complete questions on looseleaf. Answer Question # 1 on page 236. Compare and contrast DNA and RNA – in particular its shape, sugar, bases, location. (Use your binder notes, these PPT notes, and sections 4.2 and 5.2, and summary table on page 238.)Complete # 2 and # 6 on page 249. Complete # 6 on page 254.Refer to Section 5.2 to answer the following: Describe the role of the following molecules in protein synthesis: ribosomes, mRNA, tRNA,

rRNA. Differentiate between transcription & translation in terms of their purpose and location. Differentiate between a stop codon and a start codon. Provide an example of each. Complete Questions # 10, 11, 13 on page 241.