Chapter 14 & 15 Notes

Chapter 14 – How Proteins are Made

Proteins have many diverse roles

Cell signaling, hastening chemical reactions, cellular transport, transporting substances through

the blood, etc.

Genetic code is stored in DNA

Information used to produce proteins

Proteins are main players in most cellular processes.

Proteins are made from AMINO ACIDS

Hundreds of thousands of different proteins made by living things are similar in construction

20 different amino acids are assembled to make proteins

Strung together in different orders

Different lengths made different proteins

Linear chain forms a polypeptide, which can be more than 20 amino acids in length

Some amino acids are used multiple times

One or more polypeptide chains are folded into a single protein

Each protein has a particular 3-D shape, “protein conformation”

Shape is stabilized by chemical bonds

Covalent, ionic, and hydrogen

Shape determines how it binds to other molecules

How is a protein made?

DNA  mRNA  protein

DNA  mRNA – Transcription

mRNA  protein – Translation

DNA is organized into genes

Each gene directs the synthesis of a single protein, “gene expression”

Transcription – the process in which DNA’s information is copied onto mRNA. Takes place in the

nucleus of the cell.

a section of DNA unwinds and nucleotides on it form base pairs with nucleotides of

mRNA, creating a “tape”. This segment of mRNA then leaves the cell nucleus, headed for

a ribosome in the cell’s cytoplasm, where translation takes place.

A gene’s two strands of DNA are separated by RNA polymerase

One DNA strand is copied to form an mRNA molecule, “messenger RNA”

mRNA is transported to the cytoplasm

Translation – the process by which the information encoded in mRNA is used to assemble a protein at a

ribosome. Takes place in the cytoplasm.

Joining the mRNA tape at the ribosome are amino acids, brought there by tRNA. The length of

mRNA is then “read” within the ribosome. The result is a chain of amino acids linked together in

the order specified by the mRNA tape. When the chain is finished and folded up, a protein has

been made.

A ribosome reads the mRNA and assembles amino acids in the appropriate order

Assistance of transfer RNA (tRNA) is required

The polypeptide folds into a protein

DNA and RNA are similar in structure

DNA RNA

polymer of deoxynucleotides polymer of nucleotides

sugar – deoxyribose sugar – ribose

bases – A, T, G, C bases – A, U, G, C

phosphates phosphates

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Chapter 14 & 15 Notes Chapter 14 – How Proteins are Made Proteins have many diverse roles Cell signaling, hastening chemical reactions, cellular transport, transporting substances through the blood, etc. Genetic code is stored in DNA Information used to produce proteins Proteins are main players in most cellular processes. Proteins are made from AMINO ACIDS Hundreds of thousands of different proteins made by living things are similar in construction 20 different amino acids are assembled to make proteins Strung together in different orders Different lengths made different proteins Linear chain forms a polypeptide, which can be more than 20 amino acids in length Some amino acids are used multiple times One or more polypeptide chains are folded into a single protein Each protein has a particular 3-D shape, “protein conformation” Shape is stabilized by chemical bonds Covalent, ionic, and hydrogen Shape determines how it binds to other molecules How is a protein made? DNA  mRNA  protein DNA  mRNA – Transcription mRNA  protein – Translation DNA is organized into genes Each gene directs the synthesis of a single protein, “gene expression” Transcription – the process in which DNA’s information is copied onto mRNA. Takes place in the nucleus of the cell. a section of DNA unwinds and nucleotides on it form base pairs with nucleotides of mRNA, creating a “tape”. This segment of mRNA then leaves the cell nucleus, headed for a ribosome in the cell’s cytoplasm, where translation takes place. A gene’s two strands of DNA are separated by RNA polymerase One DNA strand is copied to form an mRNA molecule, “messenger RNA” mRNA is transported to the cytoplasm Translation – the process by which the information encoded in mRNA is used to assemble a protein at a ribosome. Takes place in the cytoplasm. Joining the mRNA tape at the ribosome are amino acids, brought there by tRNA. The length of mRNA is then “read” within the ribosome. The result is a chain of amino acids linked together in the order specified by the mRNA tape. When the chain is finished and folded up, a protein has been made. A ribosome reads the mRNA and assembles amino acids in the appropriate order Assistance of transfer RNA (tRNA) is required The polypeptide folds into a protein DNA and RNA are similar in structure DNA RNA polymer of deoxynucleotides polymer of nucleotides sugar – deoxyribose sugar – ribose bases – A, T, G, C bases – A, U, G, C phosphates phosphates

Transcription Takes place in the nucleus Following the production of an mRNA molecule, it must be transported to the cytoplasm Transport is through a nuclear pore Translation is ready to begin at this point Takes many players – mRNA, ribosomes, tRNA, amino acids mRNA molecules groups of three consecutive nucleotides are the functional units within mRNA molecules “codon” – an mRNA triplet that codes for a single amino acid or a start or a stop command in the translation stage of protein synthesis Each codon corresponds to a specific amino acid, e.g. AUG  methionine tRNA molecules Encoded by genes Functional as RNA molecules, but NOT translated into protein “Translates” information from mRNA to protein One region binds to the mRNA molecule “Anticodon” Base pairs with mRNA codon Another region is linked to a specific amino acid Ribosomes Organelles that are NOT surrounded by a membrane 2 components Ribosomal RNA (rRNA) Encoded by gene Not translated Forms the ribosome’s “skeleton” Proteins Attached to the rRNA scaffolding When these subunits are joined, there are 3 binding sites E, P, A tRNA bind to these sites during translation Steps of Translation

A messenger RNA transcript binds to the small subunit of a ribosome as the first transfer RNA is arriving. The mRNA codon AUG is the “start” sequence for most polypeptide chains. The tRNA, with its methionine (met) amino acid attached, then binds this AUG codon.
The large ribosomal subunit joins the ribosome, as a second tRNA arrives, bearing a leucine (leu) amino acid. The second tRNA binds to the mRNA chain, within the ribosome’s A-site.
A bond is formed between the newly arrived leu amino acid and the met amino acid, thus forming a polypeptide chain. The ribosome now effectively shifts one codon to the right, relocating the original P-site tRNA to the E-site, the A-site tRNA to the P-site, and moving a new mRNA codon into the A-site.
The E-site tRNA leaves the ribosome, even as a new tRNA bonds with the A-site mRNA codon, and the process of elongation continues

Controversies Biotechnology has generated some ethical issues Is it acceptable to advance the techniques necessary to bring about human reproductive cloning? The production of genetically modified food plants has raised commotion Recumbent DNA  two or more segments of DNA that have been combined by humans into a sequence that does not exist in nature.

Protein Synthesis and Biotechnology: From Genes to Proteins - Prof. William Barnes, Study notes of Biology

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