Genetics #2 Flashcards
Gene structure is…
Linear sequence of nucleotides with a fixed start point and an end point
Evolution of genes (3 steps)
- Gene (DNA or RNA)
- RNA (mRNA, tRNA, rRNA)
- Polypeptide (protein/amino acid)
The nucleotide sequence in a gene that has the information for amino acid placement on a polypeptide
Coding Sequences
The entire gene is a continuous coding sequence in…
Prokaryotes
The gene is split into coding and noncoding regions in…
Eukaryotes
In Eukaryotes, the nucleotide that codes for amino acids
Exons
In Eukaryotes, the nucleotide that does not code for amino acids and need to be removed by splicing?
Introns
What is the advantage of alternative splicing of introns?
- Provides for more than one polypeptide per gene
The process of making an RNA copy of a gene sequence
Transcription
The template is READ in the…. direction?
3’ to 5’ direction
The template strand of the DNA directs?
mRNA synthesis
The complimentary DNA strand is also called?
The coding strand, same nucleotide sequence of the mRNA
-This is located at the start of a gene
Promoter
Functions of the Promoter? (2)
- The recognition and binding site for the RNA polymerase
2. Helps orient the polymerase
Coding sequence begins with what DNA sequence?
3’- TAC- 5’
What is the start codon? (RNA sequence)
AUG
What signals the end of the coding region?
- The stop codon
What 2 things follow the stop codon?
- A trailer sequence
- This contains a terminator sequence that is used to stop transcription
T or F: Genes that code for tRNA may code for more than a single tRNA molecule or type of tRNA?
True
t or F: Genes that code for rRNA sequence are transcribed as a single, large precursor.
True
Special ribonucleases that remove spacers between the coding regions after transcription?
Ribozymes
3 Types of RNA that are produced during transcription?
- mRNA
- tRNA
- rRNA
Function of mRNA
Carries the message for protein synthesis
Function of tRNA
Carries the amino acids during protein synthesis to the ribosomes
Function of rRNA
Molecules that are components of ribosomes
In bacteria, this has information for 1 polypeptide?
Monocistronic
In bacteria, this has information for more than one polypeptide?
Polycistronic
In Bacteria, this has no catalytic activity but it helps the core enzyme recognize the start of genes (aka the promotor)
Sigma Factor
Holoenzyme=
A core enzyme + sigma factor
T or F: Only the core enzyme can begin transcription
True
- This is the site of transcription
- Site where DNA polymerase binds to the initiate transcription
Promotor
The sigma factor recognizes…
The specific sequences located before the transcription starting point which is recognized by specific amino acids and it helps the binding factor of the RNA polymerase to correctly position the RNA polymerase
After binding, this enzyme unwinds the DNA
RNA polymerase
Characteristics of the Transcription bubble in Bacteria…
- Moves with the polymerase as it transcribes mRNA from the template strand
- Within the bubble a temporary RNA:DNA hybrid is formed
In Bacteria, Transcription termination occurs when…
- The RNA polymerase dissociates from the template DNA
2. DNA sequences mark the end of a gene in the trailer and terminator
In Bacteria, Some terminators require the aid of an…
Rho factor for termination
Ways in which Eukaryote transcription differs from Prokaryote (5)
- Eukaryote transcription occurs in the nucleus
- RNA products must move to cytoplasm for translation
- Eukaryotic protein coding genes are Monocistronic
- Eukaryotic genes are split or interrupted (exons and introns)
- Primary transcript must undergo RNA processing before it can be translated
3 major types of RNA polymerases
- RNA polymerase II
- RNA polymerase 1
- RNA polymerase III
Function of RNA polymerase II
Cataylzes mRNA synthesis
Function of RNA polymerase 1
Cataylzes rRNA synthesis
Function of RNA polymerase III
Synthesizes the tRNA molecules
Instead of sigma factors, Archaea and Eukarya use…
Transcription factors
Proteins that bind to the DNA and line the polymerase up to it correctly
Transcription Factors
RNA transcribed from protein coding genes are called…
Primary Transcript
The Primary Transcript is…
Not the final mRNA and it can’t be translated
What doe the Primary transcript undergo in the nucleus?
Post-transcriptional Modification
Modifications of Primary Transcript result in…
The final mRNA that can be moved into the cytoplasm and translated
The 3 steps that RNA Processing includes…
- 5’ cap of 7- Methlyguanosine
- Addition of 3’ Poly-A Tail
- Removal of introns and splicing together axons
What are the functions of the cap and the tail? (3)
- Protect mRNA
- Signals that it is ready to go to the cytoplasm
- Helps the ribosome recognize the mRNA in cytoplasm
Introns are removed from the initial RNA transcript by…
RNA splicing
Slicing of the pre-RNA occurs in a large complex called?
Splicosome
When the pre-RNA is spliced so different patterns of exons remain…
Alternative Splicing
Characteristics of Transcription in Archaea…
- Polycistronic
- Polymerase II (mRNA)
- Introns
Converting the mRNA to an amino acid sequence
Translation
The relationship between specific nucleotide sequence in a gene, the corresponding mRNA, and a specific amino acid
Genetic Code
The sequence of 3 sequential ribonucleotides in mRNA that determine a specific amino acid
Codon
Characteristics of Codons
- Genetic code word (3 base pairs long)
- Complimentary to DNA triplets
- Anticodon on tRNA is complimentary
Characteristics of the Start Codon (2)
- Start site for translation
2. Always AUG
The 61 codons that specify amino acids
Sense Codons
- The 3 codons used as translation termination signals
- Do not encode amino acids
Stop (Nonsense Codons)
Up to 6 codons can code for a single
Code Redundancy
Protist exception to the stop codon
They use a single stop codon and the other 2 code for amino acids
Microbe exception to the stop codon
Some microbes incorporate 2 rare amino acids into polypeptides
- Selenocysteine
- Pyrrolysine
The synthesis of a polypeptide is directed by…
Sequence of nucleotides in mRNA
The direction of synthesis of a polypeptide goes from the __ terminal to the __ terminal?
The N terminal to the C terminal in polypeptide
In what organelle does translation occur?
Ribosomes (within the cytoplasm tho)
A complex of mRNA with several ribosomes
Polyribosome
What is the role of a tRNA?
To bring the correct amino acid to the correct codon (mRNA)
Characteristic and Function of Anticodon?
- Complimentary to the codon
- Binds the codon
- Brings correct amino acid to the codon
What end (3’ or 5’) of the tRNA binds to the amino acid?
3’ end
- This organelle is composed of protein and ribosomal RNA
- Site of protein synthesis
Ribosome
Structure of prokaryotic ribosomes
70S ribosomes = 30S and 50S subunits
What is responsible for translation on the ribosome?
Translational Domain
Peptide bond formation is catalyzed by…
Peptidyl Transferase of 23S rRNA in large subunit
During peptide bond formation, the amino group of the A site reacts with the…
Carboxyl group of the C-terminal amino acid on the P site
Peptide chain is transferred from the __ site to the __ site
P site to the A site
What are the 3 stop codons?
UAA, UAG, UGA
-These aid in the recognition of the stop codons
Release Factors
How many release factors are in Prokaryotes?
3
How many release factors are in Eukaryotes?
1
What is required for release factors?
GTP hydrolysis