Genetic Lecture 5 Flashcards
The order of the gene idea?
Chaldean Pedigree (4000 BC), Mendel’s heritable factor (1857), Darwin’s variation in traits (1859), Chromosome theory (early 20th century), Watson & Crick (1953), Genetic code deciphered (1960’s).
Chaldean Pedigree
A very very old believe pedigree of horses, where you can see the select of certain genes by crossing horses. Since the beginning of agriculture people have been trying to select different traits in livestock/plants.
Mendel’s part in the gene idea?
He figured out you have genes.
Darwin’s part in the gene idea?
That we need variation and natural selection in these genes for a population to survive.
Chromosomal Theory
Saw that you had chromosomes and thought genes might be on these.
Watson & Crick’s part in the gene idea?
It’s actually DNA that carries the genes and information.
How old is the gene idea?
The ideas of genes (that we have these packets of info that get passed along from one generation to the next) is really old.
What does one gene code for?
One polypeptide (protein)
Difference between a polypeptide and protein?
Polypeptides don’t have a function, while protein has a function and is made up of several polypeptides.
What do enzymes do?
Catylize chemical reactions.
For the game to work what must happen?
All the enzymes must be functional.
Prospero
A haploid organism (protein).
How many genes can you have on a chromosome?
Multiple
How are traits made possible?
By the presence of several different proteins.
Acetylcholine to arginine
4 steps where the precursor (acetylcholine gets transferred into arginine (important component for the organism to live).
The idea of one gene makes one polypeptide led to what?
Francis Crick’s (1957) idea of the central dogma of molecular biology. Transcription and translation (DNA to mRNA to ribosome to polypeptide).
Dogma
A set of rules that cannot change.
The 2 important principles of the central dogma of molecular biology?
Genetic information moves from DNA to RNA to protein. No information can get back the other way: protein to DNA.
Where is the gene coded on?
The template strand of DNA.
What must happen to be able to code the proper protein?
You need to have all codons perfectly back to back along the stretch of mRNA.
Codon
Sequence of three nucleotides that forms a unit to code for an amino acid.
What do eurkayotes have a lot of?
Junk DNA (what lies between the genes). They are back to back and are regulated together.
Transcription
The process by which the information in a strand of DNA is copied into a new molecule of messenger RNA (mRNA). This occurs in the nucleus.
Transcription example?
Think: photocopy of a recipe in a recipe book (the DNA ‘book’ can’t leave the library). Still instructions on a page using the same ‘alphabet’)
DNA»_space;»»»»»»»»»RNA
4 letter alphabet. 4 letter alphabet
(A,T,G,C) (A,U,G,C)
Translation
The process by which a cell makes proteins using the genetic information carried in messenger RNA (mRNA). This occurs in the cytoplasm.
Translation example?
Think: making the dish from the photocopied recipe.
Uses many ingredients
RNA»»»»»»»»PROTEIN
3 letter ‘words’ 20 ingredients
(codons) (amino acids)
The structure of a gene?
Coding sequence
START»_space;»»»»»»»»> STOP
What are the sequences recognized by?
An enzyme called RNA polymerase.
Promotor
Starts the transcription. The RNA will be sitting there until it gets a signal to start. Sometimes you need an accessory molecule that’s going to be the signal. The starting point is where the sequence actually starts.
Terminator
Ends the transcription
Transcription Unit
The sequence of DNA that is getting transcribed.
Steps of transcription?
Recognition of Promotor, Initiation, elongation, and termination
Initiation
When the RNA polymerase unwinds the DNA and creates a little bubble just bring enough to read to information and add the new nucleotides. Only the template strand will be read.
Elongation
When the RNA continues to read along the template strand and the mRNA keeps getting added on the 3’ end. The DNA rewounds after the RNA polymerase passes through it.
Direction of transcription?
Downstream
Termination
You have a sequence that tells the RNA polymerase that the gene has been finished, and you have completed the mRNA. The polymerase falls of the DNA.
Upstream
5’ end
Downstream
3’ end
An example of how genes are regulated?
Gene Activation by Vitamin D. Vitamin D is an important cofactor to activate the production if problems that are important for bone structure.
How do the RNA nucleotides attach to the DNA strand?
You have a cloud with 4 different nucleotides, each one can fit into that place, and each one has to be tried and the correct must be there before the polymerase can move onto the next position. This also occurs with tRNA and translation.
Why is the cell space small?
To maximize the interactions between the nucleotides and the DNA strand. The bases vibrate and more around very quickly in a very small volume.
3 Types of RNA Transcribed from Genes by RNA Polymerase?
mRNA, tRNA, rRNA.
tRNA and rRNA are encoded the same way as mRNA but it’s not a recipe for a protein. However, they will have a function as RNA later on.
Messenger RNA
A polymer of nucleotides that contain information
to be converted by translation into a polypeptide
(protein). Carriers gene’s messages from DNA to ribosomes.
Transfer RNA
Transport specific amino acids to the ribosome, the
protein synthesizing complex. This is important for carrying the amino acid at the proper place during translation.
Ribosomal RNA
Complexed with proteins to form ribosome. The ribosome is mostly rRNA. They translate messenger RNA into protein and polypeptides.
The Genetic Code
Consists of nucleotide bases that are read linearly in the 5’ to 3’ direction of the messenger RNA molecule, three at a time. The sequence of each triplet (codon)
specifies an amino acid.
How is the genetic code degenerate?
Because there are many instances in which different codons specify the same amino acid.
What are the codons that only code from one amino acid?
AUG (start), and UGG.
What codons don’ t encode amino acid?
UAA, UAG, UGA (stop codons).
Anticodon
The codon on the tRNA that’s the commentary pair of the codon on the mRNA.
The shape of the tRNA
An amino acid attachment at the top, anticodon at the bottom, and it has hairpin loops.
Hairpin loops
Where the tRNA folds over on itself and looks like DNA forms complementary strands (between them is hydrogen bonds).
How many ribosomes are in a cell?
Several million
What is a ribosome composed of?
One large and small subunit, that assemble around the mRNA, then it passes through the ribosome.
Small Subunit
Positions mRNA so it can be read in groups of three (codon).
Large Subunit
Removes each amino acid and joins in onto the growing protein chain.
The 3 sites of translation?
A site (aminacyl)
P site (peptidyl)
E site (exit)
The site of protein synthesis?
The ribosome (especially of A & P sites).
Initiation of Translation?
A small subunit binds to a molecular of mRNA. The arrival of a large subunit complete the initiation complex. For the large unit to attach into place energy is needed from GTP getting hydroized to GDP and inorganic phosphate.
Elongation of Translation?
tRNA enters the ribosome at the A sites and is tested for a codon/anticodon match with the mRNA. This again requires the engery from the hydroized of GTP. If it’s a correct match, tRNA shifts to the P sit and the amino acid it carries is added to the end of the amino acid chain. The whole polypeptide chain is added to the new amino acid. Peptide bonds are between these polypeptide chains. The peptide bond formation is a condensation reaction. The tRNA doesn’t move but the whole ribosome moves into the next position. Energy is also needed to remove a tRNA. It keeps going until the stop codon. (Codon recognition, peptide bond formation, and translocation).
Termination of Translation?
When the ribosome reached a stop codon on mRNA. This is a release factor (protein). The tRNA on the p site doesn’t move to the e site. Then the ribosome releases the polypeptide chain and the tRNA. The release factor promotes hydrolysis (2 GTP to 2GDP and 2 phosphates) so the two subunits can dissociate.
Can tRNA be recycled?
Yes. The amino acid and appropriate tRNA enter the active site if the specific synthesis. Then it uses ATP to get energy which then turns into AMP + 2 phosphates. The synthetase then catalyzes the covalent bonging of the amino acid to its specific tRNA.
Ubiquitous
Proteins that are everywhere. Eg. actin needed for the cytoskelen in every cell.
Gene expression
The actual making of the gene product
Why don’t we use protein instead of gene product?
Because protein isn’t always the outcome. For example, ribosomal RNA is the gene product of ribosomal DNA.
Why is the expression of genes regulated?
To conserve energy. Only make protein when we need them. This is important during development.
One nucleotide what?
Does not equal one animo acid. 2 nucleotide combinations would only specify 42 = 16
amino acids. 3 nucleotide combinations would specify 43 = potentially 64 amino acids.
