8.3 Study Guide Flashcards
What is the central dogma of biology?
A theory stating that genetic information flows only in one direction, from DNA, to RNA, to protein, or RNA directly to protein.
First proposed by Watson and Crick in 1957
What does the Central Dogma of Biology explain?
How the information stored in DNA is converted into a functional product, such as a protein. This process is called gene expression.
What are the basic steps and locations in the cell for the Central Dogma of Biology?
- DNA is copied to create more copies of itself in the nucleus.
- DNA is transcribed into RNA in the nucleus of cells.
- RNA is translated into proteins in the cytoplasm by ribosomes.
What are the structural differences between RNA and DNA nucleotides?
- RNA nucleotides have ribose sugar and DNA nucleotides have deoxyribose sugar
- RNA uses the base uracil (U) instead of thymine (T) found in DNA
What are the structural difference between RNA and DNA polymers?
DNA is typically double-stranded, forming a helix, while RNA is usually single-stranded
What are the base pairs in DNA?
Adenine (A) with Thymine (T) and Guanine (G) with Cytosine (C)
What are the base pairs in RNA?
Adenine (A) with Uracil (U) and Guanine (G) with Cytosine (C)
What is DNA Transcription?
The process where a cell copies a specific sequence of DNA into a complementary RNA molecule (mRNA).
Where does DNA Transcription take place in Eukaryotes? Prokaryotes?
Eukaryotes - Nucleus
Prokaryotes - Cytoplasm
In Transcription what is the Template Strand?
The transcribed DNA strand
In Transcription what is the Coding Strand?
The untranscribed DNA strand
What is the main enzyme of Transcription?
RNA Polymerase
What are Triplets?
Triplets are groups of three successive nucleotide bases in DNA.
What are Codons?
Codons are complementary groups of bases in mRNA.
What direction is mRNA built in?
5’ to 3’
What are the three main steps of Transcription?
- Initiation
- Elongation
- Termination
Describe Initiation
Initiation is the beginning of transcription.
It occurs when the enzyme RNA polymerase binds to a region of a gene called the promoter.
This signals the DNA to unwind so the enzyme can ‘‘read’’ the bases in one of the DNA strands.
The enzyme is now ready to make a strand of mRNA with a complementary sequence of bases.
Describe Elongation
Elongation is the addition of nucleotides to the mRNA strand.
RNA polymerase reads the unwound DNA strand and builds the mRNA molecule, using complementary base pairs.
Includes 5’ Capping
Describe Termination
Termination is the ending of transcription
Occurs when RNA polymerase crosses a stop (termination) sequence (polyadenylation site) in the gene.
Includes 3’ Poly-A-Tail Addition and removal of Introns
The mRNA strand is complete, and it detaches from DNA.
What is a Promoter?
The start site of transcription
What sequence do most Eukaryotic promoters contain?
TATA box
What does the Promoter do?
Signals transcription factor and then RNA polymerase to attach to double stranded DNA
What does an Enhancer (or Silencer) do?
Additional binding site for transcription factors
Act as a Switch
Determine if and how much RNA is made from a gene
What are Exons?
DNA sequences that carry the genetic information that is used to build proteins. (Expressed Sequences)
What are Introns?
Non-coding DNA sections that are removed during RNA splicing.
Found between exons.
Regulatory Regions (of eukaryotic genes)?
Promoter and Enhancer DNA segments
Coding Regions (of eukaryotic genes)?
Exon and Intron DNA segments
The three most important steps of pre-mRNA processing are?
- 5′ Capping
- 3′ Poly-A Tail
- Pre-mRNA Splicing
What is 5’ Capping?
A cap is added to the 5′ end of the growing transcript by a phosphate linkage. This addition protects the mRNA from degradation. In addition, factors involved in protein synthesis recognize the cap to help initiate translation by ribosomes.
What is the 3’ Poly-A-Tail?
Once elongation is complete, an enzyme called poly-A polymerase adds a string of approximately 200 A residues, called the poly-A tail to the pre-mRNA. This modification further protects the pre-mRNA from degradation and signals the export of the cellular factors that the transcript needs to the cytoplasm.
What is RNA splicing?
Removal of Introns prior to Protein Synthesis
What is Alternative Splicing?
Alternate mRNA’s produced from the same gene
Different combinations of exons are kept
Different RNA structures result in different protein structures and functions
The longer then 3’ Poly-A-Tail the longer_____?
The mRNA will be in the cytoplasm and the more protein can be made from it.
What do 5’ Capping and Polyadenylation do?
Protect mRNA from degrading enzymes on its trip from the nucleus to the cytoplasm
Compare DNA Replication and Transcription
Both…
Involve the unwinding of the DNA double helix to access the template strand.
Occur in the nucleus of eukaryotic cells.
Involve base pairing according to complementary base rules (A with T/U, C with G).
Proceed in the 5’ to 3’ direction.
Contrast DNA Replication and Transcription
Transcription produces a single-stranded RNA molecule (mRNA), while DNA replication produces a double-stranded DNA molecule.
Both processes use one strand of DNA as a template, but in transcription, only a specific region of the DNA is copied (a gene), while in replication, the entire DNA molecule is copied.
RNA polymerase is the primary enzyme in transcription, while DNA polymerase is the key enzyme in DNA replication.
In transcription, uracil (U) is used in the RNA molecule instead of thymine (T) which is present in DNA.
Transcription is essential for gene expression, allowing the genetic code to be translated into proteins, while DNA replication is crucial for cell division to ensure each new cell has a complete copy of the genome.
Can just one RNA Polymerase transcribe a gene at one time?
No, several RNA Polymerase can transcribed the same gene at the same time.
How many nucleotides does RNA Polymerase add per second?
50
What happens to the DNA strands after RNA Polymerase passes by and is finished?
It reforms the double helix
