PP8 Flashcards
Making a protein occurs in two stages:
- Transcription (writing something down in your language)
2. Translation (translating what you wrote into another language)
What is gene expression?
Gene expression: Process by which DNA directs the synthesis of proteins or various forms of RNA. A gene can be a gene that codes for a protein, or a gene can be a gene that codes for various types of RNA, which is used to make proteins.
Transcription occurs in three stages in both bacteria and eukaryotes:
Initiation
Elongation
Termination
what is transcription and where does it occur?
Transcription occurs in the nucleus in eukaryotic cells, and in the nucleoid of prokaryotic cells!
Transcription: genetic information in the form of DNA is used a template to generate a molecule of RNA (same language of nucleic acids).
what is RNA polymerase II?
RNAP II is a large polymer. RNA is polymer, so RNA polymerase is an enzyme that makes the polymer, RNA.
RNA polymerase II: 5 steps
- Binds to specific a gene region on the chromosome.
- Separates double helix (breaking hydrogen bonds between bases) at a specific gene region.
- DNA is read from 3’ 5’ and transcribed into messenger RNA (mRNA).
- Transcription therefore occurs from 5’ 3’
- mRNA strand is complementary to DNA (base pair rules). All RNA contains uracil (U) rather than thymine (T).
what is a promotor?
Promoter: The DNA sequence where RNA polymerase and attaches and initiates transcription. It includes the TATA box, which is AT rich.
describe initiation
The promoter leads to a transcription start point (nucleotide where RNA synthesis actually begins).
In eukaryotes, a collection of proteins called transcription factors bind to the promoter to allow the attachment of RNA polymerase (RNAP).
Prokaryotes also have transcription factors and a promoter for each gene, but it’s much simpler.
Once RNAP binds to the promoter, it splits the double helix by breaking hydrogen bonds. It has what is called “helicase” activity.
explain elongation
- RNAP moves down the DNA strand from 3’ -> 5’
- As RNAP moves along the DNA, it continues to untwist the double helix, exposing about 10-20 DNA nucleotides at a time.
- RNAP is said to “read” the DNA strand from 3’ 5’
- The 3’ 5’ DNA strand is called the template strand - RNAP synthesizes a mRNA transcript in the 5’ – 3’ direction.
- RNAP can only add nucleotides to the 3’ (-OH) end.
- A single gene can be transcribed simultaneously by several molecules of RNA polymerase following each other like trucks on a convoy.
explain termination.
- Once the RNAP reaches the termination sequences, a special area found after the gene on the DNA template (you do not need to know what is looks like):
- 1 rna stops transcription
- 2 RNAP detaches from DNA template strand
- 3 mRNA is released - The mRNA transcript leaves the nucleus.
What do you need to make a protein, in other words, what is needed for the process of translation?
Transfer RNA (tRNA) mRNA (product of transcription) Ribosomes (free or bound) Amino acids A dictionary of the genetic code Energy
What is translation?
Translation is performed by the ribosomes which are either attached to the RER (for proteins that will be exported or embedded in the plasma membrane) or floating around in the cytosol for proteins that will remain in the cytosol or enter the nucleus or mitochondria.
explain the 3 types of RNA:
tRNA (transfer RNA) is the smallest (about 90 nucleotides long) and is responsible for bringing in a specific amino acid for protein construction. The specificity is determined by the anticodon sequence at the bottom of the structure. This will match the codon.
mRNA (messenger RNA) is the product of transcription and will be read in the 5’ 3’ direction. Each triplet of 3 bases determines the amino acid that will be incorporated into the protein.
rRNA (ribosomal RNA) associates with ribosomal proteins to form ribosomes, which are not membrane bound, i.e., there is no membrane around them. Ribosomes are responsible for the coordination of protein synthesis.
what is a Condon?
The triplet code found on mRNA is referred to as CODONS
They are complementary to the template strand.
There are a total of____ codons
___ codons for ___ amino acids
____ codons stop translation
Most amino acids have ___ corresponding codon
There are a total of 64 codons
61 codons for 20 amino acids
3 codons stop translation
Most amino acids have > 1 corresponding codon