Biology 12 Name : ___________________

Date : ____________________

Protein Synthesis – the BIG PICTURE:

- Protein synthesis is the connection between DNA, genes and proteins.

- DNA contains _____________.- Genes are the instructions to make __________________.- The amino acid sequence is the information to make specific proteins.

- Remember: DNA can’t leave the nucleus but protein synthesis occurs in the cytoplasm … so ...

How do we get from DNA (where information is kept in the sequence of nucleotides) to proteins (where the information is kept in the amino acid sequence)?

- This requires 2 steps:1. During transcription, a single DNA strand provides a template for the

synthesis of a complementary RNA strand. This RNA molecule is called mRNA. This happens in the nucleus. The mRNA molecule is small enough to pass through the nuclear pores into the ___________.

2. During translation, the nucleic acid instructions in the mRNA molecule are converted from nucleic acid language to amino acid language. This happens in the cytoplasm at the ____________.

Location, location, location:

The key players:

- DNA – contains the __________ and the instructions to make proteins

- RNA –

- RNA is made in the ____________, but functions outside of the nucleus.- RNA Function :

o aids in protein synthesis o uses DNA strand as the template to make its strand using

complimentary base pairing

- There are 3 Types of RNA - – all are required in protein synthesis

1) messenger RNA ( mRNA ) – Job: Transcribes the chemical message encoded within the DNA and

then carries the message (instructions to make a protein) from DNA to the ribosomes (nucleus to cytoplasm)

–– Structure: A single, non-helical stand of RNA nucleotides

Each group of three bases is called a CODON. Each ____________ codes for a specific amino acid.

2) Transfer RNA ( tRNA ) - Job: The tRNA molecules transport amino acids to the ribosomes

during the translation phase of protein synthesis. tRNA will complementary base pair with mRNA strand to make polypeptide molecule

– Structure: Clover-leaf structure consisting of a single strand of RNA nucleotids folded together as a result of complementary base pairing.

o Three exposed bases are called an ANTICODON.

o _______________ are complementary to codons.

3) ribosomal RNA ( rRNA ) - Job: rRNA is produced in the nucleolus. Inside the nucleus, rRNA

joins with proteins (manufactured in the cytoplasm) to create ribosomal subunits. The subunits exit the nucleus and go to the cytoplasm via the nuclear pores. Once in the cytoplasm, they join together to cread a functional ribosome just as protein synthesis begins.

– Structure of a Ribosome:

Large subunit composed of 2 rRNA molecules and many proteins.

Small subunit composed of 1 rRNA molecule and many proteins

Subunits are held together by ________________ bonds.

P-site: Peptidyl site: location of the growing peptide chain.A-site: Aminoacyl site: docking site for tRNA molecules.

The genetic code and amino acids: - Within a DNA or RNA molecule, there are only 4 bases- But, there are 20 amino acids.- Therefore, one nucleotide is NOT sufficient to represent 1 amino acid- A 2 nucleotide code is also not enough. This would only give 42

combinations, or only enough codes for 16 amino acids-- The genetic code for a single amino acid must contain 3 nucleotide

bases. This gives 43, or 64 possible codes for amino acids.

- Each group of three nucleotide bases is known as __________. Each codon codes for a specific amino acid.

-- Some amino acids are coded for by two or more codons.- BUT, a given codon ALWAYS codes for only one amino acid.- i.e. there is redundancy but no ambiguity. - For example, GAA and _______ both mean glutamic acid