nestors microbiology chapter 7

In RNA uracil replaces what?

Thymine

What is a sigma factor and what does it do?

Sigma factor is a protein that aids the initiation of transcription. It allows RNA polymerase to bind to the promoter on the DNA. Not present in archaea and eukarya.

How does DNA get to be protein?

Starts as DNA transcription occurs in nucleus, turning it into mRNA, then gets translated at the ribosomes, which then becomes a polypeptide.

What does the genetic code start with generally?

AUG (methionine)

What is a Codon?

It is a group of 3 mRNA bases which are read together.

What do ribosomes do during translation?

The ribosomes read the transcription. It does so by directing specific tRNA towards the polypeptide chain growing it.

What is tRNA and its function?

It is the transfer RNA that binds to specific amino acids to move them.

Eukaryote ribosome

60S + 40S = 80S

Prokaryote ribosome

50S + 30S = 70S

What is an anticodon?

A sequence of three nucleotides forming a unit of genetic code in a transfer RNA molecule, corresponding to a complementary codon in messenger RNA.

Where do amino acids attach on an anticodon?

3 prime end

aminoacyl-tRNA synthetase

An enzyme that joins each amino acid to the appropriate tRNA.

How many reading frames are there?

There are only three reading frames, which depend on the start of the coding region.

What delivers amino acids to ribosomes?

tRNA, each one has a specific anticodon sequence that binds with the correct codon. After delivering, the tRNA can be recycled.

What is the genetic code?

It is 3 nucleotides which makes a codon.

Initiation of transcription

Small ribosomal subunit attaches to the mRNA, then initiator tRNA pairs with the mRNA start codon

Elongation of transcription

RNA polymerase goes down the template strand of DNA adding a complementary nucleotide

Termination of transcription

RNA polymerase reaches a terminator sequence (Stop codon) and detaches from the template

Transcription in Prokaryotes

Occurs in cytoplasm, no CAP, polyA tail, or splicing. Translation occurs simultaneously (coupled).

mRNA processing in eukaryotes

Primary mRNA transcript is synthesized by RNA polymerase II.

What is RNA polymerase II, and its function?

Transcribes all protein coding genes and noncoding RNA, lacks the ability to start transcription.

Where do genes reside?

In chromosomes

Mendels Theory of inheritance

1. Parents do not transmit traits directly to their offspring. 2. Each parent contains two copies of the factor governing the traits. 3. Alternative forms of a factor lead to alternative traits. 4. The two alleles that an individual possesses do not affect each other. 5. The presence of an allele does not ensure that a trait will be expressed in the individual who carries it.

Thomas Hunt Morgan

Used Drosophila melanogaster (fruit flies) to confirm the existence of sex-linked traits.

One gene, one enzyme

Genes are responsible for the direct production of enzymes.

Who discovered the double helix?

James Watson and Francis Crick

Who is Rosalind Franklin?

Best known for her work on DNA and X-ray diffraction photographs, critical contributions to the work of Watson and Crick.

Who are Francois Jacob and Jacques Monod?

Considered the fathers of modern genetics. They determined E. coli regulates gene expression, developed the operon model for gene expression, and discovered Lac operon functions.

What is DNA composed of?

Adenine, Guanine, Thymine, Cytosine

What are purines?

Adenine (A) and Guanine (G)

What are the pyrimidines?

Thymine and Cytosine

Nucleotide composition

Base, Phosphate, 5-carbon sugar (deoxyribose). Base attaches to #1 carbon, phosphate attaches to #5 carbon.

What has two hydrogen bonds?

Adenine and Thymine

What has three hydrogen bonds?

Cytosine and Guanine

DNA

An antiparallel structure composed of 4 nucleotides that have 3' and 5' ends. At the 3' end, hydroxyl groups allow new nucleotides to add on.

Hydroxyl group

OH, which is a hydrogen and oxygen atom available to add on new nucleotides.

Gene expression

The process by which information encoded in DNA directs the synthesis of proteins or, in some cases, RNAs that are not translated into proteins and instead function as RNAs.

Gene expression in bacteria

RNA polymerase synthesizes single stranded RNA in a 5' to 3' direction, binds to promoter (transcription starts), then stops at terminator.

RNA

Ribonucleic acid, uracil instead of thymine, single strand.

How is mRNA processed?

Primary mRNA transcript synthesized by RNA polymerase II, a 5' cap is added to 5' end, then a poly-A tail is added to 3' end.

What does capping do?

Exports mRNA out of the nucleus, prevents degradation, required to bind ribosome to subunit, promotes splicing.

Polyadenylation (Poly-A tail)

Export of mRNA from nucleus, promotes translation, prevents degradation.

mRNA splicing

Process that removes introns from pre-mRNAs and joins exons together.

Exons

Coding segments of eukaryotic DNA (useful part to coding).

Introns

Noncoding segments of nucleic acid that lie between coding sequences (not useful).

DNA polymerase III

Adds bases to the new DNA chain and proofreads the chain for mistakes; can only add at 3' end of existing strand or primer.

DNA helicase

Unwinds DNA, creates replication fork.

DNA ligase

Enzyme that chemically links DNA fragments together.

Primase

Synthesizes small RNA used by DNA polymerase III to initiate DNA synthesis.

DNA polymerase I

Removes the RNA primer and replaces it with DNA.

DNA replication steps

1. Initiation, 2. Elongation, 3. Termination.

lac operon

A gene system whose operator gene and three structural genes control lactose metabolism in E. coli.

Constitutive genes

Genes that are transcribed constantly.

Inducible genes

Not routinely transcribed.

Repressible genes

Genes are on and can be turned off.

What does an operon consist of?

Promoter, operator, structural genes, regulatory genes.

What is cAMP?

Second messenger.

What is CAP?

Catabolite activator protein.

When is CAP needed?

Only present when transcription is happening and glucose is not present.

trp operon

Tryptophan binds to the repressor protein and enables it to repress gene transcription.