Biology Chapter 6, 7, 8

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Transcription

DNA is copied into a complementary mRNA, then the mRNA IS delivered to the ribosomes in the cytoplasm

Translation

Ribosomes translate the message in the mRNA into polypeptide chains, then into proteins

mRNA (messenger RNA)

Intermediary between DNA and ribosomes, translated into proteins by ribosomes

tRNA (transfer RNA)

Transfers appropriate amino acids to ribosomes as they synthesize proteins

rRNA (ribosomal RNA)

Binds with proteins to form ribosomes

Transcription includes

Initiation, elongation, and termination.

Promoter regions

Areas of the DNA located "upstream" from the gene that is to be copied

Transcription initiation

RNA polymerase binds to the promoter region at the TATA box and begins uncoiling

TATA box

Promoter region that enables binding of RNA polymerase

RNA polymerase

An enzyme that reads a DNA strand and creates a complementary RNA strand

Transcription elongation

RNA polymerase makes a copy of the template strand in the 5 prime to 3 prime direction

Template strand

The DNA strand that is copied into an mRNA molecule during gene transcription

Coding Strand

The DNA strand that is not being copied, but contains the same sequence as the new RNA molecule

Transcription termination

Transcription is terminated when the RNA polymerase recognizes a termination sequence

Termination in prokaryotes

Transcription may be stopped by a protein binding the mRNA, or by the mRNA twisting itself into a loop

Termination in eukaryotes

A termination sequence may be a string of adenines, which will bind to the proteins and transcription stops

Capping & tailing

Poly-A tail is added to the 3 prime end of the mRNA to protect it from being digested or damaged. The 5 prime cap is also added.

Poly-A tail

A chain of adenine nucleotides

5 prime cap

A chain of seven guanines used at the initial site for attachment of mRNA's and the ribosomes

Splicosomes

An enzyme-protein complex that removes the introns from the mRNA

Introns

Non-coding sections of the mRNA

Exons

Coding sections of the mRNA

Alternative splicing

A process that produces different mRNA's from the removal of introns and combining of exons. This allows more than one polypeptide to be made from one gene.

Anticodon

The complementary sequence of base pairs on a tRNA that corresponds to the codons of the mRNA.

Pre-mRNA

Precursor mRNA are made of exons and introns. Are the immature and vulnerable single strand mRNA

Codon

A group of three base pairs that code for an individual amino acid

Wobble hypothesis

States that the rules of base pairing are relaxed at the third position, so that a base can pair with more than one complementary base

Start codon

A codon that initiates translation by signalling the start of a polypeptide.

Stop codon

A codon that causes the ribosome to terminate translation by signalling the end of a polypeptide

Translation

During translation amino acids are linked together to form a polypeptide chain which will later be folded into a protein.

Ribosome

Consists of the A site, P site, E site and two subunits

A site

Where the incoming aminoacyl-tRNA binds to the mRNA

Aminoacyl-tRNA

tRNA together with its amino acid

P site

Where the growing polypeptide chain is bound

E site

Where the empty tRNA exits and released

Aminoacylation

Process where the tRNA is bound to its corresponding amino acid

Translation initiation

Ribosomes bind to the mRNA, recognizing the 5 prime cap. Meth-tRNA starts the translation by joining the small ribosomal subunit and scanning the mRNA until it reaches the start codon. Large ribosomal subunits then bind to complete the ribosome

Translation elongation

A new tRNA+amino acid enters the ribosome, at the next codon downstream of the current codon. If the anticodon matches the mRNA codon, base pairs and the ribosome can link the two amino acids together. The empty tRNA moves to the E site and is released.

Translation termination

Termination of a polypeptide chain occurs when the ribosome encounters a stop codon at the A site. Polypeptide is released and ribosomal subunits separate.

Release factor

Protein that aids in the releasing of the polypeptide chain

Polysome

A complex formed when multiple ribosomes attach to the same mRNA to facilitate rapid translation

Housekeeping genes

Genes that are constantly needed in the cell

Transcription factors

Proteins which activate genes when required

Gene regulation

Turning off and on of genes depending on their requirements

Operon

A cluster of genes on a bacterial chromosome that is connected by one promoter and one operator

Negative feedback

The result of the process influences the operation at the process itself

Promoter

Where DNA transcription begins

Operator

Sequence of bases that controls transcription

Lac operon

Operon required for the transport and metabolism of lactose

Metabolic genes

LacZ, LacY, LacA

LacZ

Gene that codes for the enzyme that breaks down lactose

LacY and LacA

Genes that code for the uptake of lactose in the cell

Repressor protein

Binds to the operator and blocking the attachment of RNA polymerase to the promoter, thus preventing transcription of the genes

Trp operon

A group of genes that code for the components for production of tryptophan

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