Chapter 12: Gene Expression At The Molecular Level I: Production of mRNA and Proteins

Functions of Capping

(1) 7-methylguanosine structure (5' cap) is recognized by cap-binding proteins (2) Once an mRNA is in the cytosol, the cap structure helps to prevent its degradation (3) cap structure is recognized by cap-binding proteins that enable the mRNA to bind to a ribosome for translation.

3 stages of Transcription and Translation

(1) Initiation (2) Elongation (3) Termination

Functions of Poly A Tail

(1) aids in the export of mRNA from the nucleus (2) stabilizes a eukaryotic mRNA so it can exist for a longer period of time in the cytosol

Elongation

-RNA polymerase produces the RNA transcript. -sigma factor is released and RNA polymerase slides along the DNA. maintains an open complex as it goes.

Transfer RNA and Ribosomal RNA

2 examples of non-coding RNA

Capping, tailing and splicing

3 Primary mRNA needs processing

Regulatory Sequences

A DNA sequence that functions as a binding site for regulatory transcription factor proteins, which influence the rate of transcription.

Inborn Error of Metabolism (IEM)

A genetic defect that produces an inability to metabolize a certain compound. -inherited by one or both parents

Spliceosome

A large complex of several subunits known as snRNPs that removes introns from eukaryotic pre-mRNA.

Polypeptide

A linear sequence of amino acids; -Term denotes structure.

Exon

A portion of RNA that is found in the mature mRNA molecule after splicing finished

Sigma Factor

A protein that recognizes the promoter in a bacterial gene and binds RNA polymerase to the promoter.

Open Complex

A separation between 2 DNA strands that occurs near the promoter during transcription -"Transcription Bubble"

Promoter

A sequence of DNA within a gene that controls when and where transcription begins.

Terminator

A sequence of DNA within a gene that specifies the end of transcription

Start Codon

A three-base sequence—usually AUG—that specifies the first amino acid in a polypeptide.

Codons

A three-nucleotide sequence of DNA or mRNA that specifies a particular amino acid or a stop codon; codons function during translation.

Gene

A unit of heredity -At the molecular level, a organized unit of base sequences in a DNA strand that can transcribed into RNA and ultimately results in the formation of a functional product.

Transfer RNA (tRNA)

An RNA that carries amino acids and is used to translate mRNA into polypeptides

Ribosomal RNA (rRNA)

An RNA that forms part of ribosomes, which provide the site where translation occurs.

Recessive

An individual with a disease has inherited the mutant (defective) gene that causes it form both parent

Central Dogma

DNA -> transcribed--> RNA -> translated --> Protein

Template Strand

DNA strand that is used as a template for RNA synthesis or DNA replication

polypeptide

Each protein-encoding gene stores the info for the production of a ____.

RNA polymerase

Enzyme that synthesizes strands of RNA during gene transcription

Initiation

First stage in the process of transcription or translation

Protein

Functional unit composed of one or more polypeptides -Term denotes function

Gene Expression

Gene function either at the level of traits or at the molecular level

Protein-Encoding Genes

Gene that serves as a template to make an mRNA molecule that contains the info to specify a polypeptide with a particular amino acid sequence

Cytoplasm

In Bacteria, both, transcription and translation occur in the ___.

Nucleus and Cytosol

In Eukaryotes transcription occur in the ____ and translation occurs in the ____.

Pre-mRNA

In eukaryotes, the mRNA transcript before any biochemical modifications are made to it.

3

In eukaryotic genes, protein components contain ____ forms of RNA Polymerase.

RNA

Instead of accessing the info directly, a working copy of the DNA, composed of ____, is made. -occurs by the process of transcription

Introns

Intervening DNA sequences that are found in between the coding sequences of genes.

Gene Function

Mutations affect the genetic blueprint by altering ____.

Functional Protein

Once a polypeptide is created, it becomes a unit within a ____.

RNA Splicing

Process by which the introns are removed from RNA molecule and the remaining exons are joined together.

Transcription

Produces an RNA copy of a gene

Initiation

Protein called sigma factor binds to RNA polymerase. -completed when the DNA strands are separated near the promoter to form an open complex -about 10-15 bp long

Transcription Factors

Proteins that influence the ability of RNA polymerase to transcribe genes.

Non-Coding RNA

RNA ! and III are responsible for transcribing ____. Ex. tRNA and rRNAs

Protein-encoding genes

RNA II is responsible for transcribing the mRNA from eukaryotic ____.

Non-Coding RNAs (ncRNAs)

RNA molecule that does not encode the amino acid sequence of a polypeptide.

5

RNA polymerase II of eukaryotes always requires ___ transcription factors to initiate transcription

Messenger RNA (mRNA)

RNA that contains the info to specify a polypeptide with a particular amino acid sequence.

snRNP

Small Nuclear RNA

Genetic Code

Specifies the relationship between the sequence of bases in the codons found in mRNA and the sequence of amino acids in a polypeptide.

Introns and Exons

Splicing involves the removal of ___ and the linkage of ___.

Alternative Splicing

Splicing of introns in a pre-mRNA that occurs in different ways, that allows the production of 2 or more different polypeptides from the same gene.

One-Gene/One Enzyme Hypothesis

Suggest that one gene encodes one enzyme. -later modified (4 ways) -hypothesis by Beadle and Tatum

Coding Strnad

The DNA strand opposite to the template -has same sequence of bases as resulting mRNA except it has uracil instead of thymine

RNA Modification

The biochemical modification of an RNA

Degenerate

The characteristic of the genetic code is that more than one codon can specify. the same amino acid

Structure and Function

The expression of genes at the molecular level affects the ____ and ____ of cells. This determines the traits that an organism expresses.

Mature mRNA

The final product that results when the pre-mRNA in eukaryotes undergoes processing events before it exits the nucleus

Termination

The final stage of transcription, in which the RNA dissociates from the DNA; or of translation, which the polypeptide is released form the ribosome.

Elongation

The second stage in transcription or translation, where RNA strands or polypeptides are made respectively.

Exons

The segments that are retained in a mature mRNA

False

True or False: Bacteria and Eukaryotes have the same number of RNA polymerase that transcribes all genes.

False

True or False: DNA to RNA to Protein is the only pathway.

True

True or False: Exons are considered expressed regions because they contain the coding sequence for a polypeptide

True

True or False: For genes to be expressed, the info in them must be accessed at the molecular level.

True

True or False: In a bacteria, the poly A tail has an opposite effect, causing the mRNA to be rapidly degraded.

False

True or False: In the case of alkaptonuria, if an individual inherited the mutant gene from both parents they would be able to produce the normal enzyme that would be able to metabolize homogentistic acid.

False

True or False: Introns are found in all eukaryotic genes

True

True or False: Introns are found in bacteria, but rarely.

True

True or False: Introns are intervening regions that are not expressed, because they are removed from the pre-mRNA

True

True or False: Introns occasionally occur in rRNA and tRNA molecules of certain species

False

True or False: Most proteins function as enzymes.

True

True or False: One or more polypeptides form a functional protein

True

True or False: Some genes produce non-coding RNAs that do not specify the amino acid sequence of a polypeptide.

True

True or False: Some mRNAs are spliced into alternative ways to produce two or more polypeptides, that way a single gene can encode more than one polypeptide

True

True or False: Spliceosome is regulated at times, so the splicing of a given mRNA can occur in 2 or more ways.

False

True or False: Splicing is more common in unicellular eukaryotic species rather than complex eukaryotes.

False

True or False: The first base in the codon is the degenerate.

True

True or False: The genetic code consist of 64 different codons.

True

True or False: The info to make all proteins is contained within genes.

False

True or False: The poly A tail is encoded in the gene sequence.

False

True or False: Transcription alters the the structure of DNA permanently.

True

True or False: Translation is used b/c a base sequence in an mRNA is "translated into an amino acid sequence of a polypeptide.

False

True or False: rRNA and tRNA are removed by the action of spliceosome.

False

True or False: the process of central dogma is the same bacteria, archaea and eukaryotes. Meaning they all use transcription and translation.

Protein-Encoding Genes

What are most genes?

Genes

What contains the information necessary to produce an organism and allow it to interact with its environment?

To carry info from the DNA to cellular components called ribosomes

What is the function of mRNA?

enhanced, inhibited

When a regulatory protein binds to a regulatory sequence, some proteins are ____ and others are ____.

Nucleus and Cytosol

When all of the RNA modifications have been completed the mRNA leaves the ____ and enters the ____, where translation occurs.

Amino acids are found in 20 different types

Why are there 64 codons?

Ribozyme

a biological catalyst that is an RNA molecule

Poly A Tail

a string of adenine nucleotides at the 3' end of most mature mRNAs in eukaryotes -usually 100 to 200 nucleotides in length -added enzymatically after a pre-mRNA has been completely transcribed

Hemoglobin (2 genes)

a-globin and 2 B-globin polypeptides Example

Mutations

changes in the genetic material that can be inherited

Self-Splicing

refers to RNA molecules that can remove their own introns without the aid of other proteins or RNA - Ex. rRNA and tRNA

Splicing

removal of introns

Capping

the process in which a 7-methylguanosine is covalently attached at the 5' end of pre-mRNAs of eukaryotes

Translation

the process of synthesizing a specific polypeptide on a ribosome

Preinitiation Complex

the structure of the completed assembly of RNA polymerase II and GTFs at the TATA box prior to transcription of eukaryotic protein-encoding genes

When capping occurs

when a pre-mRNA is being made by RNA polymerase. transcript is only 20 to 25 nucleotides in length