Chapter 7 Flashcards
Definition: Central Dogma
the fundamental principle of molecular genetics, which states that genetic information flows from DNA to RNA proteins
Definition: TransCription
Mechanism by which the information coded nucleic acids of DNA is copied into the nucleic acids of RNA ; something rewritten in the same language
Definition: TranSlation
Mechanism by which the information coded in nucleic acids of RNA is copied into the amino acids of proteins
How does RNA and DNA differ?
Single; double
AU; AT
OH on 2’ carbon for RNA; instead of deoxyribose
Definition: mRNA
The end product of the transcription of a gene; mRNA is translated by ribosome into a protein.
It is the intermediate between DNA -> cytosol-> to nucleus
Definition: (trasnfer) tRNA
A carrier molecule that binds to a specific amino acid and adds the amino acid to the growing polypeptide chain
It is a block ‘t’ shaped works like converter belt as it matches the codons to the appropriate amino acids.
It is short and loops itself to form antiparallel double strands that complement each other
Is tRNA antiparallel?
It is short and loops itself to form antiparallel double strands that complement each other in terms of base pairs in between each loops
Definition: ribosomal RNA (rRNA)
An RNA molecule within the ribosome that bonds the correct amino acid to the polypeptide chain ( A P E)
Defintion: RNA polymerase
An enzyme that reads a DNA strand and creates a complementary strand of RNA
If the DNA template strand is read form 3’ to 5’ what will the mRNA strand read?
Since mRNA is complementary to the DNA strand it will read 5’ to 3’
Definition: Template strand
The DNA strand that is copied into an mRNA molecule during gene transcription . This DNA strand is read by RNA POLYMERASE
What reads the DNA template strand?
RNA polymerase
Why is the first step of DNA replication called transcription
The template strand is a DNA strand that is transcribed into a precursor mRNA molecule
Defintion: pre-mRNA
- Cannot be used to produce a protein
As a result needs to be modified to become an mRNA strand
Where does transcription occur?
DNA and mRNA are found in the nucleus
What is translation for dummies !
- mRNA associates with a ribosome
- the amino acids coded by the mRNA are delivered to tRNA, then to the ribosome
- The amino acids join together to from polypeptides chains
Definition: Genetic code
The specific coding relationship between bases and the amino acids they specify; the genetic code can be expressed in terms of either DNA or RNA bases
Defintion: codon
A group of THREE base pairs that code for and individual amino acid
Definition: start codon
The codon that signals the start of a polypeptide chain and initiates translation. First codon translated in any mRNA in both prokaryotes and eukaryotes
AUG
Defintion: stop codon
A codon that signals the end of a polypeptide chain and causes the ribosome to terminate translation
UAA, UAG, and UGA
How does protein synthesis actually stop using the stop codon?
Unlike, the other codon the THREE stop codons are not affiliated with amino acids therefore when used there is NO amino acid for the ribosome to read therefore the polypeptide chain is released.
Defintion: Promoter
A nucleotide sequence that lies just before a gene and allows for the binding of the RNA polymerase
Definition: TATA box
A region of the promoter that enables the binding of RNA polymerase. The RNA polymerase is able to recognize this region by the amount of thymine and adenine bases, since they contain only a double bond it takes less energy to break.
How does the process of transcription begin?
It starts as the enzyme RNA polymerase binds to the DNA and unwinds it near the beginning of a gene.
Is the TATA box on the DNA or RNA
ASK MRS
Transcription- Initiation
Defintion: Coding strand
The DNA strand that is not being copied by contains the same sequence as the new RNA molecule
Definition: Termination sequence
A sequence of bases at the end of gene that signals the RNA polymerase to stop transcribing
Definition: Poly (A) tail (hair and makeup)
A chain of adenine nucleotides that are added to the 3’ end of the pre-mRNA molecule to protect it from enzymes in the cytosol
Definition: 5’ cap
A sequence of seven Gs that is added to the start of a pre-mRNA molecule; ribosomes recognize this site and use it as the sit of initial attachment
Definition: Exon
A sequence of DNA and RNA that codes for part of a gene
Definition: Intron
A non-coding sequence of DNA or RNA. Prokaryotes do not contain introns
Definition: Spliceosome
An enzyme-protein complex that removes introns from the mRNA
Definition: Small ribonucleoprotein (snRNP)
A protein that binds to introns and signals them for removal
Are genes constantly be produced and realeased?
No, they are controlling mechanism used to control gene release. As a result, they are not constantly in production
What are housekeeping genes?
Housekeeping genes are genes that MUST be produced regularly in order to survive.
In constant transcription and translation
What are examples of processes housekeeping genes control?
Housekeeping genes regulate metabolism, growth, and DNA replication
What are examples of processes housekeeping genes DO NOT control?
liver cells repair enzymes and toxins in the body and genes that produce hemoglobin give rise to red blood cells
What two molecules control gene control in prokaryotes?
Lactose and trytophan
Examples of negative feedback system
Definition: Lac operon
A type of gene expression. A cluster of THREE genes that contains the DNA sequences to regulate the metabolism of lactose
Where do prokaryotes get lactose from?
Since they are simple celled organisms they need to obtain lactose from their surroundings. Gene are required to metabolize lactose
What three things does the lac operon consist of
- Promoter (where DNA transcription begins)
- Operator (sequence of bases that control transcription )
- Coding regions (where the metabolism will actually occur)
Defintion: Operator
The region in the operon that regulatory factors bind to
Defintion: Repressor protein
A protein that binds to the operator to repress gene transcription
When is the lac repressor active ?
The lac repressor is active when there is an absence of lactose. It keeps RNA polymerase from to binding to the promoter region.
But when lactose is present the lac repressor in INACTIVE
What does the lac repressor do?
The lac repressor regulates the production of the lactose-metabolizing proteins
Defintion: Inducer
A signal molecule that triggers the expression of an operon’s gene
What is the inducer for the lac operon ?
Lactose prevents the lac repressor from working
What happens when Lactose is present ?
Lactose (inducer molecule ) binds to lac repressor, causing it to be INACTIVE by changing its shape. As result it is NOT able to bind
The three enzymes that metabolize lactose are synthesized and start to break down lactose in the cell
Why is the lac operon known as an inducible operon?
Because the inducer INACTIVATES the repressor thus allowing the gene that breakdown lactose to be be transcribed
What is Tryptophan ?
Tryptophan is an amino acid that most prokaryotes are able to synthesize independently but can also take it up directly if it available in the environment
The operon that regulates the production of tryptophan in a cell is called the trp operon
What is the difference between the lac repressor and the trp repressor?
The lac repressor protein in inactivated by a signal molecule
The trp repressor protein is activated by a signal molecule
What occurs in the presence of tryphtophan ?
the trp repressor protein is ACTIVATED in the presence of tryptophan)
What occurs when tryptophan is absent?
Trp repressor protein is inactive; does not bind to the operator and block transcription-> RNA polymerase binds to promoter and TRANSCRIPTION of trp operon occurs
What occurs when tryptophan is present?
Tryptophan (co repressor ) binds to trp repressor protein activating it and enabling it to bind to the operator
Transcription of the trp operon is BLOCKED (conserves energy uses available tryptophan present)
What is a co-repressor (operon genes)
a signal molecule that binds to a regulatory protein to reduce the expression of an operon genes
The difference between eukaryotic cells and prokaryotic for control mechanism of genes ?
Since eukaryotic cells are more complex we do not have operon systems :(
What are the four categories for eukaryotic cells ?
- Transcriptional (as mRNA is synthesized)
- Post-transcriptional (as mRNA is processed)
After transcription- during translation - step 3 & 4 - Translational (a protein is synthesized)
- Post- translational ( after protein is synthesized)
Explain Step 1: Transcriptional (as mRNA is being synthesized)
Regulates which genes are transcribed into mRNA or the rate of transcription)
RECALL: - DNA is wrapped around histones
- Promoters are no accessible for transcription
- keeps gene promote inactive
How many types of transciptional regulation models exist ?
3 models exist !
What occurs during model 1 of regulation ?
Model #1: activator molecule binds upstream of gene’s promoter, displacing histones and exposing promoter
What occurs during model 2 of regulation ?
Signals acetyl group to be added to histones
loosens histones association with DNA exposing promoter
Proteins (general transcription factors ) accumulate of TATA box of promoter
Provides a substrate for RNA polymerase to attach and begin transcription
What occurs during model 3 of regulation ?
Methyl group (CH3) is added to cytosine bases in the promoter inhibiting transcription
Puts genes “on hold” until they are needed
When needed, specialized enzymes remove methyl groups and allow transcription to begin
- What is Post Transcriptional Regulation (as mRNA is processed) ?
Example 1: Alternative splicing- Different mRNAs are produced from pre-RNAs by removing different combinations of introns
Example 2: Binding Making Proteins to mRNA- prevents mRNA from being translated
E
xample 3: Change to Rate mRNA breakdown - Regulated by hormones
What is 3. Translational Regulation ?
Changing length of poly (A) tail [hair and makeup] affects the rate of translation
Specific enzymes can add or delete sequences of adenine at end of mRNA
Can affect time required to translate mRNA into a protein
What is 4. Post-Translational Regulation?
a) Processing of proteins is required to render it active (control the availability of active proteins)
b) Chemical modifications - Chemical groups added or deleted affecting its function
How is cancer a lack of regulatory mechanisms ?
The constant lengthening of telomeres is one way that cancer cells can grow out of control
The probability that a given sequence of DNA has experienced a mutation increases over the lifespan of an organism
The reason many forms of cancer occur most often during old age
What do cancer cells lack?
Cancer cells lack the regulatory mechanisms that keep healthy cells under control .
What are genetic mutations ?
Genetic mutations are changes in the DNA sequence cause various factors.
Eg. chemicals, radiation, and incorrect replication
What is a small scale mutation?
A small-scale mutation involves an individual base pair called points mutations
Definition: Point mutations
A change in a single nucleotide within a gene
What are the three categories of mutations called ? SID
Substitution, insertion, deletion, or inversion
Defintion: Substitution
The replacement of one base pair in a DNA sequence by another base pair
Definition: Insertion
The addition of a base pair (small-scale mutation) or larger coding region (large-scale mutation) from a DNA sequence
Definiton: Deletion
The removal of a base pair or larger coding region from a DNA sequence
Definition: Inversion
Two adjacent bases trading places or the reversal of a sequence of DNA
Definition: Single nucleotide polymorphism (SNP)
A difference in the DNA between individuals caused by point mutations
Defintion: Missense mutation
A change of a single base pair or group of base pairs results in the code for a different AMINO ACID. The protein that is created will have a different sequence and structure, and it may be non-functional or function differently. Can be good if it creates a desirable effect
Defintion: Nonsense mutation
Results in a PREMATURE STOP CODE in the gene. The polypeptide is cut short and most likely will be unable to function
Definiton: Silent mutation
One or more base pair does not affect the functioning of the gene. The mutated DNA sequence codes for the same amino acid as the non-mutates sequence, and resulting protein in not altered
Definition: Frameshift mutation
one ore more nucleotides are inserted into or deleted from a DNA sequence, causing the READING OF CODONS TO SWITCH = missense and nonsense effects .
