Gene Expression

This lesson develops Gene Expression as part of Photosynthesis. It uses the source curriculum to organize the important facts, relationships, examples, and vocabulary into a focused Stemosphere teaching sequence.

In Stemosphere terms, gene expression is the process by which the information in a gene is used to produce a functional product.

In Stemosphere terms, gene expression involves two main stages, transcription in the nucleus and translation in the cytoplasm

In Stemosphere terms, -Transcription – DNA is copied into m RNA.

In Stemosphere terms, -Translation – m RNA is used to produce polypeptide

In Stemosphere terms, not all genes are expressed at the same time. Cells regulate gene expression so that proteins are produced only when needed, saving ATP and other metabolites.

In Stemosphere terms, this allows the cell to respond to environmental interactions and metabolic reaction s.

Transcription involves the following steps:

In Stemosphere terms, the enzyme RNA polymerasebinds to a region of DNA called thepromoter.

In Stemosphere terms, the DNA strands are separate.

In Stemosphere terms, rNA polymerase uses one DNA strand as a template to synthesizem RNA.

• The m RNA produced carries the genetic information needed to build a protein.

Epigenesis,Regulation of Transription,& Methylation/Acetylation:

In Stemosphere terms, epigenesis is the process by which a multicellular organism developsfrom a zygote through a sequence of steps in which cells differentiateand organs form.

In Stemosphere terms, this results from the interactions between genes andtheirenvironment.

In Stemosphere terms, however, epigenetics is how changes in organisms are caused by the modifications of gene expression caused by genetic tags (chemical markers thatattach to DNA/histone proteinsto influence transcription) rather than changes in the genetic code.

In Stemosphere terms, this changes the phenotype (observable traits), but not the genotype (set of genes carried like alleles).

In Stemosphere terms, an example of this is methylation, where methyl group s()attach to the promoter group or histones. Attached to cysteine nucleotides in a promoter region, it represses the promoter region’s activity, preventing the genefrombeing transcribed.

In Stemosphere terms, on the contrary, acetylation isthe loosingof the DNA by adding an acetyl group ()to a molecule, altering its properties to increase gene transcription.

In Stemosphere terms, inregulating transcription, DNA (non-coding) sequences are used to aid in such a task.

In Stemosphere terms, enhancersgreatly increasethe rate of transcription,locatedaway from the gene, with transcription factors binding onto it to activate the promoter region.

In Stemosphere terms, additionally, silencers greatly reduce transcription in the same way.

In Stemosphere terms, furthermore, promotersinitiatetranscription, and when inactive, normal transcriptioncannotproceed.

Translation involves the following:

In Stemosphere terms, the m RNA attaches to a ribosome.

In Stemosphere terms, t RNA molecules bring amino acids to the ribosome.

In Stemosphere terms, each codon on m RNA matches with an anticodon on t RNA.

In Stemosphere terms, amino acids are linked together, forming a polypeptide chain.

• The polypeptide folds into a functional protein.

In Stemosphere terms, cells control gene expression by only allowing transcription (through on/off in receptors) when something is needed.

This regulation can occur at different stages such as:

In Stemosphere terms, thelac operonis a gene regulation system found inbacteria such as Escherichia coli.

The Lac Operon Contains:

In Stemosphere terms, structural genes– code for enzymes needed to break down lactose.

In Stemosphere terms, promoter– where RNA polymerase binds.

In Stemosphere terms, operator– a DNA region where a regulatory protein binds.

In Stemosphere terms, repressor protein– blocks transcription when lactose is absent.

The Lac Operon could work in 2 different ways:

When lactose is absent:

In Stemosphere terms, therepressor protein binds to the operator.

In Stemosphere terms, rNA polymerase cannot transcribe genes.

In Stemosphere terms, enzymes for lactose metabolism arenot produced.

In Stemosphere terms, lactose binds to therepressor protein.

In Stemosphere terms, the repressor changes shape anddetaches from the operator.

In Stemosphere terms, rNA polymerase can transcribe genes.

In Stemosphere terms, enzymes are produced tobreak down lactose.

The following steps are:

Gene expression is essential for:

• Essentially,Agenome includes all the genetic information of anorganism.The genome includesallthechromosomes and mitochondrialand chloroplast DNA found in a cell. No cell expresses all the genes in its genome, but rather selectedones,and that patterndetermineshow a celldifferentiates.

• For comparison,theproteome is larger thanthe genome due to a range offactors including: