Unit 6: Protein Synthesis and Gene Expression/Regulation Flashcards
RNA
Ribose sugar. Uracil instead of thymine. Single stranded. The sequence of the RNA bases, together with the structure of the RNA molecule determines RNA function
mRNA
carries genetic information from DNA to the ribosomes. Information is used to direct protein synthesis.
codon
three base sequence found on mRNA.
tRNA
helps create a specific polypeptide sequence at the ribosomes as directed by mRNA. Various types of tRNA, each carrying a specific amino acid
anticodon
three base sequence found on tRNA. Correct base pairing of tRNA anticodons with mRNA will result in the release and addition of an amino acid to a growing polypeptide
rRNA
functional units of ribosomes responsible for protein assembly. Base pairings of anticodons and codons occurs in the ribosome. Creates primary polypeptides as tRNA releases amino acids.
microRNA
small RNA molecules that bind to other RNA molecules to degrade them
Gene Expression
- process of using a gene to generate either a protein or a functional RNA
- The gene contains a series of nucleotides which are ‘read’ by cellular enzymes to produce a protein or functional RNA
- The order of nucleotides in the gene determines the amino acids which will be joined to produce a protein
- Different genes have different nucleotides which code for different proteins.
Where are proteins assembled in eukaryotes?
Proteins are assembled at the ribosomes, which can be free-floating in the cytoplasm or attached to the rough endoplasmic reticulum (RER) in eukaryotic cells.
Exons
- the coding regions of a gene that are retained in the mRNA and will be translated into protein
- only in eukaryotes
Introns
- the non-coding regions of a gene that are removed during RNA splicing and do not contribute to the final mRNA product or protein
- only in eukaryotes
Promoters
- region of the gene that is a specific sequence of DNA that signals the start of transcription
- usually extends several dozen nucleotide pairs upstream of the start point
TATA box
crucial promoter in forming the initiation complex in eukaryotes
RNA Polymerase and its Role in Creating mRNA
- binds to the promoter region of the DNA
- RNA polymerase reads the DNA template strand in the 3’ to 5’ direction
- It then starts synthesizing an mRNA strand by adding complementary RNA nucleotides (A, U, C, G) in the 5’ to 3’ direction.
- When RNA polymerase reaches the terminator sequence of base pairs on the DNA template strand, it completes the production of pre-mRNA and releases it into the nucleoplasm.
base pairs in RNA
A (adenine) pairs with U (uracil)
G (guanine) pairs with C (cytosine)
transcription factors
helps RNA polymerase bind to the promoter
In eukaryotes RNA polymerase joins with several transcription factor proteins at the promoter (a special sequence of base pairs on DNA that signals the beginning of a gene)
This combination is called the transcription initiation complex.
template strand
- The DNA strand that RNA polymerase adds bases to in 5’ to 3’ direction
- also called the noncoding strand, minus strand, or antisense strand
- mRNA strands base pairs are going to be complementary to the base pairs on this
coding strand
- the side of the DNA that is not used by RNA polymerase because it is not in the 3’ to 5’ direction
- the base pairs for the mRNA are the same as the base pairs for the coding strand except with U switched with T because it was coded to be complimentary with the template strand
terminators
- region of the gene that tells the RNA polymerase to stop coding the strand
- in prokarytes, the mRNA will go straight to being translated after this
- in eukaryotes, the mRNA has to be processed, so it is just pre-mRNA now
pre-mRNA
- initial form of mRNA that is transcribed from DNA in the nucleus of eukaryotic cells before it undergoes processing to become mature mRNA
- It contains both introns (non-coding regions) and exons (coding regions)
- eukaryotes only
Processing of Pre-mRNA: what is added on
- A poly-A tail is added to the 3’ end of the mRNA transcript
- This modification helps protect the mRNA from degradation, aids in the export of the mRNA from the nucleus to the cytoplasm, it protects it rom hydrolytic enzymes, and plays a role in the initiation of translation
- A GTP cap is added to the 5’ end of the mRNA transcript, it is a modified guanine nucleotide
- It helps protect the mRNA from degradation, facilitates the binding of the ribosome for translation, and aids in the export of the mRNA from the nucleus
- this is done by enzymes in the nucleus
Processing of Pre-mRNA: splicing
- Splicing done by spliceosomes
- stay in the nucleus; do not code for proteins. They are non-coding sequences (introns are in between sequences)
- exit the nucleus to go to the ribosome; do code for proteins
- They are the real genes
- They code for proteins (exons expressed)
Alternative splicing
Alternative mRNAs produced from the same gene
Translation: Initiation
- A cell translates an mRNA message into protein with the help of transfer RNA (tRNA)
- Small ribosomal subunit binds to mRNA and an initiator tRNA, Then the large ribosomal subunit attaches
- Each tRNA molecule carries a specific amino acid to the ribosome based on the mRNA’s codons