Download Protein Synthesis Is a Major Function of Cells

Protein Synthesis Is a Major Function of Cells
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DNA
Transcription
Takes
place in
the
nucleus
mRNA
Translation
Amino Acid
chain, a
Takes
place on
a
ribosome
Polypeptide
The general steps in protein
synthesis
Protein
Figure 4.7 Function of ribosomes
Transcription
Translation
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1. Transcription is the process of copying the DNA
sequence of a gene into a mRNA transcript
• Takes place in the nucleus
2. Translation is the process of copying the mRNA
transcript into a sequence of amino acids which
will eventually become a protein
• The mRNA than moves to a ribosome, either
attached or free
• Free ribosomes are found in the cell’s
cytoplasm
• Produces proteins for use within the
cell
• Attached ribosomes are found on the
endoplasmic reticulum
• Produces proteins for use in the cell
membrane or is exported outside of
the cell
The pathway for proteins being used for the cell
membrane or for export out of the cell
1. Nucleus → site of transcription: DNA → mRNA
2. mRNA travels to a ribosome on the endoplasmic
reticulum: RER
3. RER → site of translation: mRNA → amino acid
sequence: a polypeptide
4. The polypeptide then travels through the RER into
the Smooth ER and then to the Golgi body
5. The polypeptide is modified by the SER and Golgi
body
6. A vesicle forms on the outside of the Golgi body and
then pinches off
7. The vesicle moves through the cytoplasm and fuses
with the cell membrane
Figure 4.9 Golgi
apparatus (graygreen) and transport
vesicles
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Figure 4.14 The organelles of the endomembrane system
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The general steps in protein
synthesis
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The general steps in protein
synthesis
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