PROTEIN SYNTHESIS

PROTEIN SYNTHESIS

Read pages 56 to 58 in text. Complete pg 17 in HO. Please read tomorrows section on photosynthesis.

Protein synthesis involves a set of complex interactions between various organelles. This is important to the survival of the cell because proteins make a large number of different molecules from enzymes, hormones, structural and transport proteins.

Protein synthesis can be divided into two main processes

TRANSCRIPTION and TRANSLATION

TRANSCRIPTION takes place in the NUCLEUS
the information required to make a protein is carried on a segment of chromatin (DNA) called a GENE the BASE SEQUENCE on the gene will determine the type of protein made

The following is a sequence of events that takes place in order to transcribe a gene:

1.The site at which the gene is located on the DNA UNCOILS and EXPOSES the base sequence

2.Only ONE SIDE of the DNA is used as a TEMPLATE to copy the information into messenger RNA (mRNA)

3.Free floating ribonucleotides (RNA) in the nucleoplasm will pair up with their complementary base pairs on the coding DNA strand.

DNA ...............................................RNA

Thymine-Adenine............................ Adenine-Uricil(Replaces Thymine)

Cytosine-Guanine ............................Cytosine-Guanine


4.As the RNA nucleotides are joined together, the mRNA strand is RELEASED from the DNA and the DNA recoils into its double helix

5.Once the gene is completely transcribed it is released and moves into the CYTOPLASM through a nuclear pore


TRANSLATION

1. once the mRNA is in the cytoplasm, the ribosomes will attach to the mRNA
strand.
2. the ribosome covers six bases on mRNA
3. the code on mRNA is read three bases at a time
4. these three bases are called a CODON
5. each codon codes for one amino acid
6. transfer RNA (tRNA) is the molecule that carries the amino acid to the
ribosome and mRNA
7. tRNA has a triplet of bases (anticodon) that is complimentary to the mRNA
codon
8. each ribosome can hold two tRNA
9. once the two tRNA anticondon are paired correctly with the mRNA codon, the
ribosome will join the two amino acids together by forming a PEPTIDED BOND
10. the first tRNA is then released from the ribosome and will pick up another
amino acid
11. the ribosome will move down one codon and the second tRNA moves into the f
first position with the growing polypeptide chain
12. a new tRNA move in the open position with its amino acid and the steps are
repeated
13. once the ribosome reaches the end of the mRNA strand they are released from
each other
14. the polypeptide chain will then fold into its functional shape.