17 Gene Expression

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_______ specify proteins to be made

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Genes

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RNA (Ribonucleic Acid):

the components of a nucleotide

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5- carbon sugar (Ribose)

phosphate group

nitrogen-containing base (one of 4)

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What are RNA (Ribonucleic Acid)Nitrogen-containing bases?

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Uracil (U)Cytosine (C)Adenine (A)Guanine (G)

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a segment of DNA serves as a template for mRNA production;

a Transcript is formed

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TRANSCRIPTION

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RNA leaves the nucleus through ?

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pores in the nuclear envelope

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3 Need to Know(s) about RNA

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RNA is a Single Strand

RNA is Transcribed from a Section of DNA

DNA is a Template for RNA formation

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Define the process of transcription

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DNA is used as a template to make a complementary sequence of mRNA

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Define the process of translation

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synthesis of a polypeptide under the direction of mRNA. Translates codons to amino acids at ribosomes

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where does translation occur in a eukaryotic cell

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cytoplasm

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in eukaryotes, what is the pre-mRNA called?

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the primary transcript. It's only called this in the nucleus, before modification.

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Write the central dogma of molecular genetics, as proclaimed by Francis Crick:

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DNA -> RNA -> Protein.

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Stages of Protein SynthesisTranscription consists of:

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- Initiation- Elongation- Termination

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Initiation

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Initiation factors bring together mRNA and tRNA carrying 1st amino acid met.

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Elongation

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Amino acids are added one by one to the preceding amino acid. Stimulated by elongation factors.

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Termination

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codes for a stop signal and release factor binds.

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Transcription Summary

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RNA polymerase assembles RNA from 5’ to 3’ direction

No primer needed

Transcription begins at Promoter

Transcription Unit is copied

Terminator signals the end

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Stages of Protein Synthesis in Prokaryotes

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Bacteria have no nucleus

no mRNA processing

No nuclear envelope

No Transcript Processing occurs in Prokaryotes!RNA is mature immediately

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Stages of Protein Synthesis in Eukaryotes

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Eukaryote have nucleus, pre-mRNA is processed before leaving nucleus

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Transcription Elongation

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**Eukaryotic Transcription ElongationRNA polymerase moves along DNA template strand joining complementary RNA nucleotides to 3'end of RNA transcript **New RNA peels away from template strand **Template strand re-forms a double helix with nontemplate strand

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Transcription Termination in Prokaryotes

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Prokaryotes have terminator sequence in DNA that transcribes an RNA terminatorPolymerase detaches from DNA, transcript is released

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Transcription Termination in Eukaryotes

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DNA has polyadenylation signal sequence *RNA polymerase II transcribes signal AAUAAA in pre-mRNA *Proteins bind to signal, cut pre-mRNA free

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Explain the functions of the APE sites.

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A site holds the tRNA carrying the next amino acid to be added to the chain. P site (start site) holds the tRNA carrying the growing polypeptide chain. E site is where discharged tRNAs exit the ribosome.

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Distinguish between introns and exons:

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Introns are noncoding segments of nucleic acid between coding regions. Exons are expressed regions that exit the nucleus.

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What are UTR's?

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untranslated regions: parts of mRNA that won't be translated to protein but have functions like ribosome binding. located at the 5' and 3' ends.

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what are 3 important functions of the 5' cap and the poly-A tail?

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1. The seem to help facilitate the export of the mature mRNA from the nucleus 2. They protect the mRNA from degradation by hydrolytic enzymes3. They help ribosomes attach to the 5' end of the mRNA once it reaches the cytoplasm.

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What is the TATA box?

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a crucial promoter DNA sequence.Upstream from start pointNeeded to form initiation complexTATA Box must bind to DNA before RNA polymerase II can bind

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List 3 important facts about the promoter:

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1. The transcription start point (the nucleotide where RNA synthesis begins) is included in the promoter2. Determines which of the two strands are used as the template3. needs transcription factors (in eukaryotes) to mediate the binding of RNA pol + initiation of transcription.

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How do spliceosomes work?

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spliceosomes interact with certain sites along an intron, releasing it and joining the exons that were around it. They catalyze this process, participate in spliceosome assembly, and splice site recognition.

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3 nucleotides =

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1 codon

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1 codon represents

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1 amino acid

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what is the start codon?

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AUG is “start” codon, codes for Methionine

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Three types of RNA

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messenger RNA (mRNA)transfer RNA (tRNA)ribosomal RNA (rRNA)

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Messenger RNA (mRNA)

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carries a coded message from DNA to the cytoplasm3 nucleotides on mRNA = 1 Codon1 Codon represents 1 amino acidThe Genetic Code lists all possible codons of mRNA and the amino acids they represent

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Transfer RNA (tRNA)

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transfers amino acids to mRNAinvolves codon-anticodon interaction

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What is an anticodon?

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a nucleotide triplet at the bottom of the tRNA that base pairs to the codon of the mRNA so the amino acid can detach.

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Description & Function of mRNA:

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Messenger RNA: modified single strand chain of nucleotides that are complementary to DNA. Carries the message of genes, of what proteins to make

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Description & Function of tRNA:

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a tRNA has an anticodon one one end and an amino acid on the other end. Functions to transfer amino acids from the cytoplasm to the mRNA, at the ribosome

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Description & Function of rRNA:

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Description & Function of rRNA:ribsosomal RNA: molecules that make up a ribosome, where mRNA's message is translated to amino acids.V

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Ribosomal RNA (rRNA)Binding sites:

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A site, P site, and E (exit) site for tRNA

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ribosomes are made in the

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nucleolus

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Ribosomal RNA (rRNA)

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structural component of ribosome; assemble proteins during translation; ribosomes have large and small subunits

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Initiation of Translation

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Small ribosomal subunit binds to mRNA; Initiator tRNA binds to Start Codon; Start Codon is AUG; Codes for amino acid MethionineLarge ribosomal subunit binds; GTP provides energy

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Signal-recognition Particle (SRP)

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Enables proteins to direct their destination

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Coupled Transcription & Translation in Prokaryotes

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Polyribosomes (Polysomes) are groups of ribosomes reading same mRNA simultaneouslyEnable making of many copies of protein simultaneously

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POINT MUTATIONS

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Changes in a single nucleotide pair of a gene

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Effect of Point Mutations:Silent

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no effect

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Effect of Point Mutations: Missense

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changes 1 amino acid to another

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Effect of Point Mutations: Nonsense

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changes codon to “stop” codon

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Effect of Point Mutations: Frameshift

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alters reading frame / ALTERS EVERYTHING AFTER ERROR

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What is the function of RNA polymerase

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It unwinds the double helix and adds nucleotides to a growing strand of RNA.