PROTEIN SYN

THESIS

(EUKARYOTES)

B Y AN T A R A , C

A R L A , CL A R I S

S AN D T

H E A N T A Y

DNA is located in the nucleus of a cell. It is a double helix shape and contains

sequences of nucleotides. Each nucleotide has one of the 4 bases:

Adenine (A) which always bonds with Thymine (T), and Cytosine (C) which always bonds with Guanine (G). Each stand of DNA

is complementary to the other.The order of these nucleotides determines

holds the genetic code for a protein.

DNA

Nucleotides

The section of DNA that codes for the protein being synthesized is unwound and unzipped by the enzyme helicase.

DNA UNWINDS

Helicase

One half of the DNA is the template strand. This is the strand

that will be transcribed into mRNA. The other strand is the coding (anti-sense) strand. This has a

complementary sequence of bases as in the template stand so

contains the same sequence of nucleotides as will be in the mRNA

that will be produced.

TWO STRANDS OF DNA

Template

Strand

Coding Strand

RNA polymerase attaches to the template strand and creates a complementary length of mRNA. This is the primary mRNA.The coding stand of DNA is not used.

RNA SYNTHESIS

mRNA

Coding Strand

RNA Polymerase

Template

Strand

DNA:- Has the bases

Adenine, Cytosine, Guanine and Thymine

- Very long- The sugar-phosphate

backbone is made of deoxyribose sugar

- Double stranded

RNA:- Has the bases

Adenine, Cytosine, Guanine and Uracil

- Relatively short- The sugar-phosphate

backbone is made of ribose sugar

- Single stranded

DIFFERENCES BETWEEN RNA AND DNA

During RNA processing, which occurs in the

nucleus, the introns in the primary mRNA are

spliced out leaving only the exons in the mature

mRNA.

RNA PROCESSING

Intron

Exon

Primary mRNA

The mature mRNA leaves the nucleus through a nuclear pore to go into the cytoplasm.

LEAVING THE NUCLEUS

mRNA

Nuclear Pore

Nucleus

Cytoplasm

The ribosome attaches to the mRNA in the cytoplasm.

It reads the codons (3 bases) in the mRNA that each code for a

specific amino acid. The tRNA with the complementary

anticodon to the codon will carry the specific amino acid.

TRANSLATION

Ribosome

mRNA

tRNA loaded with Amino Acids

Amino

Acid

The tRNA with the correct anticodon will be attracted to the binding site in the ribosome. The ribosome will add the amino acid it carries to the growing polypeptide chain and the tRNA will be released.The unloaded tRNA will be reattached to another of the same amino acid.

TRANSLATION

Ribosome

Binding SiteLoaded

tRNA

mRNA

Unloaded tRNA

Polypeptide Chain

The completed chain of amino acids, called a polypeptide chain, is a primary protein.

PRIMARY PROTEINS

Polypeptide chain - Primary protein

SECONDARY PROTEINS

The polypeptide chain arranges into two common shapes to form a secondary protein: the alpha helix (left) and the beta-pleated sheet (right). These are held in place by hydrogen bonds.

The alpha helix and beta pleated sheets fold into a complex 3 dimensional shape which is called a tertiary protein. For some proteins, this is the end of the road and the protein goes away to do what is was synthesized to do.

TERTIARY PROTEINS

Quaternary proteins are clusters of tertiary proteins which bind together to form one protein that does a specific job.

QUATERNARY PROTEINS