Chapter 12 Flashcards
We can look at gene function in two ways
Molecular function of the protein
Organisms trait
They are connected, the molecular function affects the structure and function of cells
Polysome
One mRNA and many ribosomes
Unit of heredity
Another name for a gene
Two things genes do
proteins, template for
Store the info to make proteins
Act as a template to make an RNA molecule
Mutations
Changes in genetic material that can be inherited. It may change genetic blueprint by altering gene function
Archinold garrod and the relationship between genes and enzymes
Studied the disease
What the disease causes
What he hypothesized the disease was the result of
Alkaptonuria which causes abnormal levels of homogentisic acid(alkapton)
Causes discoloration of skin and urine to be black
Due to a missing enzyme, called it an inborn error of metabolism which is
A mutation in a gene that’s inherited by one or both parents
Beasley and Tatum
Proposed WHAT hypothesis
Describe their experiment, with bread mold neurospora
One gene, one enzyme; genes carry the info to make enzymes so a mutation in a gene would cause a defect in an enzyme
The bread mold needs a carbon source(sugar) inorganic salts and biotin.
They found every mutation resulted in the need for a vitamin to be supplemented
Beadle and Tatum
Amino acid arginine Sequence of conversions Group 1 Group2 Group 3
Arginine needs 3 enzymes to grow,
Sequence of conversions
EnZyme 1 converts a precursor into”orinthine “, enzyme 2 converts to citrulline, and enzyme 3 converts to arginine.
Group 1 was missing the first enzyme. It would grow if o, c or a was added
Group 2 was missing enzyme 2. Wouldn’t grow if only orinthe was missing but would grow if c or a was added
Group 3 missing enzyme 3 could only grow if arginine was added
4 ways the one gene one enzyme hypothesis was modified
Modified slogan
- the info to make all proteins including enzymes is in genes
- some proteins are made of 2 or more polypeptides
- A single gene can encode more than 1 polypeptide. Sometimes due to the way rnas are spliced
- Some genes encode RNAs that form things other than protein, like ribosomes
One gene, one polypeptide
Polypeptide
Polypeptide denotes_____
Protein denotes —-
Protein activity determines
A linear sequence of amino acids. Polypeptide denotes structure, protein denotes function
The structure and function of cells
How proteins made of one polypeptide differ from those made with more
In those ones one gene contains all the info to make the whole protein
Hemoglobin
The protein that carries oxegyn in red blood cells. Made of 2 xglobin and 2 bglobin polypeptides
Central dogma ( steps of gene expression at molecular level)
- Transcription- messenger RNA (mRNA) specifies the amino acid sequence of a polypeptide.
Translation - uses mRNA template to make a polypeptide. Called translation because nucleotide sequence in mRNA is translated into an amino acid sequence of a polypeptide
DNA->RNA-> protein
Central dogma summary
The transcription of DNA into mRNA and the translation of mRNA into a polypeptide
mRNA is an example of a ____ gene
What do those genes do
Two important products of non structural genes
Structural gene
Code for polypeptides
Transfer RNA which translates the language of mRNA into amino acids
and ribosomal RNA which forms part of ribosomes where translation occurs
tRNA
rRNA
Transfer RNA translates mRNA into amino acids
Ribosomal RNA part of ribosomes
Stages of transcription
Prokaryotes
Initiation, recognition step
In bacteria sigma factor causes RNA polymerase to recognize promoter region
Stage completed when DNA strands separate near promoter to form open complex
Transcription second stage(prokaryotes)
Which strand is used
What base pair is subsitutied
Elongation RNA polymerase synthesizes RNA Template or coding strand used for RNA syntheses Synthesized to 5' 3' Uracil is substatitute for thymine
Transcription stage 3(prokaryotes)
Termination
RNA polymerase reaches the termination sequence
Causes both the polymerase and newly made RNA transcript to dissociate from the DNA
The main purpose of the genetic material is
To encode the production of proteins in the correct cell, at the right time, in the right amount
A gene at the molecular level is defined as
An organized unit of DNA to be transcribed into RNA and ultimately result in a functional product
In eukaryotic cells ( transcription)
Polymerase 1 and 3
Polymerase 2
Polymerase 1 and 3 transcribe nonstructural genes
Poly 2 transcribes structural genes, transcribes mRNA
RNA processing in eukaryotes How it's different from bacteria Intron Exon Splicing
Eukaryotic mRNAs have a pre mRNA form that requires processing into mature mRNA
Coding sequence in structural genes, they’re transcribed but not translated
Coding sequence found in mature mRNA
Removal of introns
What is a cap, when is it added, what’s it’s function
What’s a tail, when’s it added what’s its function for
Addition of tails and caps in RNA processing (eukaryotes)
A cap is a form of guanosine attached to the 5’ end
Added when pre mRNA is made
It’s function is to be recognized by the cap binding proteins which allow mRNA to exit nucleus and bind to ribosomes
A tail is 100-200 adenine nucleotides added to the 4’ ending . Added after pre mRNA is made
Aids in export of mRNA from nucleus and gives stability to mRNA
Self splicing
How they do it
Ribozymes
rRNA and RNA.
RNA catalyze removal of intron
An RNA molecule that catalyze a a chemical reaction like self splicing
Splicing
Where it happens
Spliceosome
Alternative splicing
Removal of introns
Happens at branch site 5’ splice site and 3’ splice site
Removes introns precisely. Made of small nuclear RNA AND proteins
Splicing can occur more than one way to produce different products
Genetic code
Codon
What do they do
Degenerate code
Sequence of bases in an mRNA molecule
Group of 3 nucleotide bases
They specify a particular amino acid exp. ggc meand glycine
More Than one codon can specify the same amino acid
Bacterial mRNA
Where is the ribosomal binding site
What’s the start codon, what does it define
What’s the stop codon aka termination code
How long is a typical amino acid
5' ribosomal binding site AUG, methionine Defines the reading frame, or the order I which the codons are read UAA, UAG, or UGA A few hundred amino acids long
What shifts the reading frame
Aiddtion of a nucleotide base which throws off all the other codon
Substitution to base in mRNA
T is substituted with U
tRNA ANTICODON
ANTICODON is a three base sequence in a tRNA molecule that is complementary to mRNA, causing them to bind together.
Exp, is the ANTICODON in tRNA is 3’ AAH5’ then its complementary to a 5’ UUC 3’ codon. UUC is for phenylaline, so that tRNA molecule will carry phenylaline.
90% of energy in ecoli is used
To transcript mRNA into polypeptides
Translation requires more components than transcription because the sequence of codons in mRNA must be translated into a sequence of amino acids according to the genetic code
What are four of the components translation requires
mRNA
tRNA
RIBOSOMES
TRANSLATION FACTORS
Common factors of a tRNA molecule (3)
Different tRNA molecules are encoded by different genes
What they carry is in their name, tRNAser carries serine
Cloverleaf structure
ANTICODON
Acceptor stem for amino acid binding
Aminoacyl-tRNA Synthetase What it does How Many are therea Reactions result in ( 2 names for that product) Where it attaches The second genetic code refers to
Catalyzes attachment of amino acids to tRNA
There’s one for each of the 20 different amino acids
Reactions result in tRNA with amino acid attached (charged tRNA or amino acid tRNA)
Attaches to the 3’ end
The ability of each aminoacyl- tRNA synthetase to recognize the right tRNA
4 steps of aminoacyl tRNA synthetase
- Specific amino acid and atp bind to aminoacyl tRNA synthetase
- the amino acid is activated by the covalent bonding of AMP and a pyrophosphate is released
- the correct tRNA binds to the synthetase. The amino acid is covalently attached to the tRNA and amp is released
- the charged tRNA is released
RIBOSOMES
Nickname for them
Site where what takes place
Prokaryotes have ____ kind of ribosome which____
Eukaryotes have distinct RIBOSOMES in different compartments but right now we’re focusing on ____
Structural differences between prok and euk exploited by antibiotics to inhibit _____
Molecular machine
Translation
One kind of ribosome which translates all mRNAs in cytoplasm
Here we’re focused on cytosolic RIBOSOMES
Bacterial RIBOSOMES
RIBOSOMES shape determined by
P site
A site
E site
Determined by rRNA
Peptidyl site
Aminoacyl site
Exit site
Stages of translation
Summary of what happens
3 part Explanation of what happens
Two eukaryotic differences in initiation
Initiation, elongation, termination
mRNA first tRNA and ribosomal subunits assemble
mRNA binds to the small ribosomal subunit
Initiator tRNA binds to the start codon in mRNA
Large ribosomal subunit binds
MRNAs have a guanosine cap at 5’ end instead of a ribosomal binding cap
Position of the start codon can vary more. Many times first AUG codon is used as the start codon
Step 2
Summary
Step by step (4)
Synthesis starts from start codon to stop codon
Aminoacyl tRNA brings a new amino acid to the a site
Binding occurs due to codon/ ANTICODON recognition
Peptide bond is formed between the amino acid at the a site and the growing polypeptide chain
Movement (translocation) of the ribosome toward the 3’ end of the mRNA by one codon
Termination
What happens
How many stop codons/ what are they
Release factors
When a stop codon is found in the a site, translation ends
There are 3 stop codons, UUA UAG UGA
These are what recognize the stop codon and bind to it at the a site
