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Biotech 1

QuestionAnswer
What size are prokaryotes and what do they not contain? 1-5μm They do not contain any internal membrane bound structures (organelles)
What size are eukaryotes? 10-100μm and they have membrane bound organelles that are specialised to perform particular functions.
Are prokaryotes or eukaryotes fast growing and capable of producing large amounts of relatively simple proteins very quickly while having simple growth requirements? Prokaryotes.
Which are more expensive to grow and produce proteins more slowly but are capable of making more complicated proteins with various modifications? They also command a high price. Eukaryotes.
Do prokaryotes and eukaryotes store their genetic information in the form of DNA? Yes.
Genes that code for proteins are involved in the production of? Amino acids Nucleotides essential metabolites and in the mediation of: replication transcription translation cell growth catabolic pathways energy-generating systems responses to environmental changes
Which genes are expressed continuously? Only genes that encode the proteins that maintain basic cellular functions are expressed continuously.
What happens to the transcription of remaining structural genes? It is regulated.
When can a cell can regulate gene expression at? The level of transcription. The level of translation. Post-translational control.
How can a cell regulate gene expression at the level of transcription? If gene product (a protein) is not needed, a gene is not transcribed (no mRNA is made)
How can a cell regulate gene expression at the level of translation? mRNA can be stable (capable of being translated many times) or unstable (degrades quickly so it is only translated a small number of times)
How can a cell regulate gene expression at post-translational control? After it is made gene product (protein) can be activated/inactivated by a chemical modification. This could be achieved by the addition of a methyl or phosphate groups, carbohydrate chains and small peptides.
Where is DNA found in prokaryotes? DNA is found freely floating around a region of the cell cytoplasm called the nucleoid.
How is DNA found in prokaryotes? The DNA is supercoiled so that it may fit inside the cell.
How are DNA supercoils stabilised? By association with proteins, but most of the DNA is "naked", i.e. freely accessible to the transcription factors.
What do supercoils allow? Supercoils and the lack of nuclear envelope allows direct contact between DNA and the ribosomes and makes it possible for prokaryotes to couple the processes of transcription and translation together, which makes protein synthesis faster (more efficient)
Where is prokaryote DNA contained? In the: bacterial chromosome - which contains all the genes necessary for growth and reproduction. One or more plasmids - extrachromosomal DNA which carries genes which give additional characteristics that may confer survival advantage.
How is gene expression achieved in a prokaryotic cell? Almost exclusively by the control of transcription.
If a particular protein is required by a prokaryotic cell what happens? A signalling system involving transcription factor proteins initiates transcription - the gene is turned 'on' or expressed. If a protein is not needed in transcription of the gene is tuned off - the gene is not expressed.
How are bacterial genes organised? Bacterial genes of related function are clustered together on the bacterial chromosome in structures called operons.
What two basic gene types are found within an operon? Structural genes which code for proteins needed for normal operation of the cell e.g. breakdown of sugars. Regulator genes which code for proteins that regulate genes (switch their expression on or off), particularly the structural genes within the operon
What does an operon allow? An operon allows for co-ordinated control of the genes - if one gene is on, all genes in an operon are on, or if one is off, all are off. Operons therefore control the expression of group of proteins of related function that are always produced together.
Explain an inducible operon? Genes controlled by an inducible operon are usually not expressed and need to be switched on.
Explain a repressible operon? Genes that are controlled by a repressible operon are continually expressed until they are switched off.
What two types of operon are there? Repressible operons and inducible operons.
What can E.coli use as an energy source? Lactose, however it is not the preferred sugar source if glucose is also present. To save energy and resources, E.coli does not make enzymes to import and digest lactose unless it is actually going to use it.
If lactose is the only available sugar what does the bacteria need to do? Switch on the production of these enzymes.
Where are the genes for the required enzymes to break down lactose found? Clustered in the lac operon.
What three structural genes are there in the lac operon? β-galactosidase (hydrolyses lactose into glucose and galactose) Permease (transmembrane channel that allowes lactose to enter the cell) Transacetylase.
What is the expression of the structural genes controlled by? A single upstream promoter; the site where RNA polymerase binds to transcribe a single strand of mRNA, that can be translated to produce the three enzymes.
Gene (R) codes for what? A repressor protein that an bind to the operator. Repressor gene is continually expressed (repressor protein is always present).
What happens in the absence of lactose? The repressor protein binds to the operator. This blocks access of the RNA polymerase to the promoter. Therefore the structural genes are not transcribed.
What happens in the presence of lactose? Part 1 Some lactose enters the cell and binds to the repressor protein. The shape of the repressor is altered so that it can no longer bind to the operator. RNA polymerase now can bind to the promoter.
What happens in the presence of lactose? Part 2 The structural genes are transcribed into mRNA. The structural proteins are translated into proteins.
What is the lac operon an example of? An inducible operon because the structural genes are normally inactive and must be induced - ie. they are switched on by an inducer molecule (lactose). This saves the cell wasting energy.
In the Trp operon what happens to the enzymes required for the cell to make tryptophan if tryptophan is already present? They are repressed. Only if there is no tryptophan available to the cell that it needs to switch on the genes to make it's own tryptophan.
Where does the main regulation of gene expression occur in prokaryotic cells? At the trascriptional level. i.e. genes are either switched on or off.
Where do transcription and translation take place in a prokaryotic cell? Within the cytoplasm.
How much post-translational modifications occur in a prokaryotic cell? Little to none.
How much more DNA do eukaryotic cells contain than prokaryotic? Roughly 2m of DNA per cell in a diploid human cell vs. only 1.6mm of DNA in the cell of E. coli.
Where is the vast majority of DNA contained in a eukaryotic cell? In the nucleus.
How is DNA organised in eukaryotic cells? Into multiple chromosomes which are linear.
How do eukaryotic cells pack negatively charged DNA very tightly? As it is wound round positively charged proteins called histones.
146 base pairs wound twice around a histone core called a? Nucleosome.
Actively transcribed regions existing as loosely packed are called? Euchromatin.
DNA regions that are not transcribed and are packed very tightly are called? Heterochromatin.
Is heterochromatin transcribed? Yes.
Where does transcription and translation take place in eukaryotic cells? Transcription - nucleus Translation - cytoplasm
What is the default expression state in prokaryotes? "Off"
In eukaryotes transcription factor proteins bind to where? The promoter sequences but some can also bind further away to the short DNA sequences called enhancers.
Transcription factors bound to enhancers act as what? Activators (increasing the likelihood that transcription of that particular gene will occur).
Where can enhancers be located? Upstream of a gene, within the coding region of the gene, downstream of a gene, or may be thousands of nucleotides away.
What are enhancers usually? Tissue specific and provide another way of controlling gene expression at the level of transcription.
How many genes does the human genome encode for? 25,000 genes, the genome contains 6.4 billion base pairs.
Do some bases within the genome have no known function? Yes.
Non-coding regions named introns are found within many genes, is this true? Yes.
What are expressed regions called? Exons.
What is the mRNA transcribed directly from the eukaryotic genome called? Primary transcript mRNA and it contains both introns and exons.
As introns do not code for polypeptide sequences they must be removed from the primary transcript mRNA before translation into a polypeptide, what is this called? Splicing.
How is primary mRNA transcript modified in eukaryotic cells? By the addition of a polyA tail and a 5' cap.
Most eukaryotic mRNAs carry a poly (A) tail about how long? 150-200 bases long on their 3'-ends.
What does the poly (A) tail seem to do? Protect mRNA from degradation. The longer the poly A tail is the more stable the mRNA transcript seems to be.
How many times can stable mRNA molecules be translated? Multiple times.
Unstable mRNA moles are degraded quickly so only a few copies of the protein can be made, true or false? True.
Posttranscriptional gene regulation
The 5'-ends of eukaryotic mRNAs are blocked with structures called caps. What dual purpose do caps serve? The protect messages from degradation. They help with attachment to ribosomes for translation.
Some mRNAs have alternative splice sites that do what? Change the final protein product.
By altering the exons which are spliced together it is possible to do what? Make many different final proteins. This means that the number of mRNAs (and therefore proteins) produced by a cell can be much higher than the number of genes in the genome.
Unlike prokaryotes, do most eukaryotes have operons? No.
mRNA is produced as a primary transcript where? (Eukaryotic) In the nucleus.
Mature mRNA is then transported through a nuclear pore into where? The cytoplasm for translation.
What happens after the poly (A) tail and 5' CAP are addded to the mRNA? It is then processed to remove introns and splice together exons.
How do prokaryotes and eukaryotes regulate gene expression? Prokaryotes tend to regulate gene expression almost exclusively at the level of transcription. Eukaryotes regulate the activity of many gene products (proteins such as enzyme) by using post-translational modifications.
What do post-translational modifications usually involve? Covalent addition of chemical groups to either amino acid side chains or protein's C or N termini, or preoteolytic cleavage or a pro-protein to make an active protein.
How can post-translational modifications extend the chemical repertoire of the 20 standard amino acids? By introducing new functional groups such as phosphate, acetate, amide groups, or methyl groups.
What is phosphorylation? Adding a charged phosphate group catalysed by enzymes called kinases. It is a very common mechanism for regulating the activity of enzymes and is the most common post-translational modification.
What is glucosylation? Many eukaryotic proteins have carbohydrate molecules attached to them in a process called glycosylation, which can promote protein folding and improve stability as well as serving regulatory functions.
Other forms of post-translational modification consist of? Cleaving peptide bonds, as in processing a propeptide to a mature form.
Created by: Cleggat
 

 



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