9.5 How Genes Are Regulated

To function properly, a cell must have the right amount of necessary proteins.

The organisms and cells control how their genes are transcribed and translated.
In a simple unicellular organisms, each cell controls when and how its genes are expressed.
There needs to be a way to control when a gene is expressed and how much of it is made and when it's time to stop making it.

Cells in multicellular organisms look different and perform different functions.

A muscle cell and a liver cell are very different from a skin cell.

There are different sets of genes in each cell.
Cells have certain basic functions that they must perform for themselves.
Many genes that are not expressed by other cells are expressed by each cell, which can carry out its specialized functions.
Cells will turn on or off certain genes at different times in response to changes in the environment or during the development of the organisms.
Unicellular organisms turn on and off genes in response to the demands of their environment so that they can respond to special conditions.

Malfunctions in the control of gene expression can lead to the development of many diseases, including cancer.

To understand how genes are regulated, we must first understand how a gene becomes functional in a cell.

The process occurs in both prokaryotic and eukaryotic cells.

The processes of translation and transcription occur at the same time.

The transcription stops when the protein is no longer needed.
The primary method to control what type and how much is expressed in a prokaryotic cell is through the regulation of DNA transcription.

The next steps happen automatically.

More transcription occurs when moreProtein is required.
In prokaryotic cells, the control of gene expression is almost entirely at the transcriptional level.

Lactose can be used as a food source when the genes are transcribed.

There is a region called the operator between the promoter and the three genes in the operon.
When there is no Lactose, a repressor binding to the operator and preventing the polymerase from binding to the promoter is what happens.
The products of the three genes are very small.
The end product of lactose metabolism binding to the repressor is what prevents it from binding to the operator.
The ability to bind to the promoter and freely transcribe the three genes allows the organisms to metabolize the lactose.

Eukaryotic cells are more complex and have more of the same features as eukaryotic cells.

The newly synthesised mRNA is taken out of the nucleus and into the cytoplasm.
The processes of translation and transcription are separated from one another by the nucleus.
Gene expression can be regulated at all stages of the process.

Eukaryotic genes are expressed in the nucleus as well as in the cytoplasm.

Post-translational modifications of proteins may lead to further regulation.

It takes place in the nucleus before the translation of the genes.

There is a process of translation between the cytoplasm and the rest of the body.

When different combinations of introns and exons are removed from the transcript, alternativeRNAs allows different products to be produced from one gene.

More often than not, this alternative splicing is controlled by the cell as a way to control the production of different products in different cells, or at different stages of development.
70% of genes in humans are expressed through alternative splicing, according to one estimate.

There are five basic ways to do alternative splicing.

There are segments of pre-mRNA with exons in blue, red, orange, and pink.

Introns have a beginning and ending recognition sequence, and it is easy to imagine the failure of the splicing mechanism to identify the end of an intron and find the end of the next intron, thus removing two introns and the intervening exon.

There are mechanisms in place to prevent exon skipping, but they are likely to fail.
It's more than likely that the "mistakes" will produce a nonfunctional protein.
Alternative splicing is the cause of many genetic diseases.
Alternative splicing would allow for the creation of a new variant without the loss of the original one.
Gene duplication is an important part of the evolution of new functions by providing genes that may evolve without eliminating the original function.

The model of the double-helix structure was proposed by Crick.

The molecule is made of nucleotides.
There is a nitrogenous base, a five-carbon sugar, and aphosphate group.

There are four nitrogenous bases in DNA, two purines and two pyrimidines.

The molecule is composed of two strands.

Each strand is made up of a group of nucleotides that are bound together by a bond between the deoxyribose sugar of the next and thephosphate group of one.
The bases are extended from this backbone.
The double helix is caused by the bonding and the two strands spiral around each other.
The second nucleic acid in cells is called ribonucleic acid.
There is a single strand of nucleotides.
It contains the sugar ribose, rather than the deoxyribose and the uracil that is found in DNA.
VariousRNA molecule function in the process of forming genes from the genetic code.

There is a single, double-stranded circular chromosome in prokaryotes.

Double-stranded linear DNA is packaged into chromosomes.
The helix is wrapped around something.
The chromosomes become even more coiled during meiosis, as they become even more coiled to facilitate their movement.
There are two distinct regions in chromosomes which can be distinguished by staining, reflecting different degrees of packaging, and whether the DNA in the region is being expressed or not.

A semi-conservative method in which each of the two parental DNA strands act as a template for new DNA to be synthesised is the basis of 9.2 DNA Replication.

Each strand of DNA has one parent and one daughter.

Replication in prokaryotes starts from a single origin of replication, while it starts at multiple origins in eukaryotes.

The replication fork is formed when the DNA is opened.
It is possible to add only one direction to the synthesis of an RNA primer by Primase.

The leading strand is the strand that is continuously synthesised in the direction of the fork.

The other strand is made in a different direction from the replication fork.

The lagging strand is a strand.

The DNA is sealed with a ligase after it is replicated.

The ends of chromosomes can't be extended without a primer.

Telomerase extends the ends by copying the RNA template and extending one end of the chromosomes.

The primer can be used to extend the DNA.
The ends of the chromosomes are protected.
Errors are made in replication and cells have mechanisms for repairing it.
The mechanisms include mismatch repair and excision repair to remove bases that are damaged.

In prokaryotes, a promoter sequence on the DNA template is used for synthesis.

New mRNA is synthesised by longation.
The mechanism that causes the fall off of the DNA template is called atranscription.
A cap and a poly-A tail are used to modify newly transcribed eukaryotic mRNAs.
The structures help export mature mRNA from the nucleus.
Introns are removed and exons are reconnected with single-nucleotide accuracy when otic mRNAs undergo splicing.
The nucleus contains only finished mRNAs.

The flow of genetic information in the cell is described in the central dogma.

The process of translation and the process of transcription are the two main ways in which genes are used.
There is a genetic code between the codon and an acid.
The genetic code is translated by the tRNA molecule into a specific codon.
There are only 20 and three stop codons in the genetic code.
This means that there are more than one codon.
Every species on the planet has the same genetic code.

The players in translation are ribosomes, tRNAs, and various enzymatic factors.

The ribosomal subunit binding to the template.
The translation begins at the beginning of August.
According to the genetic code, the formation of bonds occurs between the sequential amino acids.
The ribosome accepts charged tRNAs, and as it steps along the mRNA, it bonds between the new and the end of the growing polypeptide.
The ribosome is translated in three steps.
When a stop codon is encountered, a release factor binding the components and frees the new one.

Not all cells within an organisms contain the same genes.

Not all of the genes in a cell are expressed at the same time.

When they are needed, the genes are expressed.

Any given cell has a subset of the DNA that is expressed by otic organisms.
Each cell type has its own way of regulating the amount and type of protein.
The first step in the process of expression is the translation of the DNA intoRNA.
These processes occur almost simultaneously in prokaryotic cells.
The translation that occurs in the cytoplasm is different from the translation that occurs in the nucleus.
Gene expression is only regulated at the transcriptional level in prokaryotes, whereas in eukaryotic cells it is regulated at the epigenetic, transcriptional, post-transcriptional, and posttranslational levels.

The replication fork is isolated from a cell strain.

There is a mechanism for repairing errors in c. 3 DNA.

A promoter is a person.

Portions of the eukaryotic mRNA sequence are regulated after transcription is removed.

Take the following DNA sequence and translate it.