lecture 5 Flashcards
(18 cards)
protein synthesis
Proteins are necessary for cell function.
Protein synthesis is under direct nuclear direction. DNA carries the genetic code that is used to create every protein.
The information a cell needs to make a specific protein is contained in a segment of DNA known as a gene.
Gene – a region of DNA that contains the information needed to make a functional piece of RNA, which in turn can make a protein.
???
Protein synthesis uses 20 amino acids.
The sequence of amino acids in a protein determines its structure and function.
The amino acids needed to make a specific protein is dictated by the genetic sequence of the gene that codes for that protein.
DNA contains 4 nitrogenous bases (A, T, C, G) that control the synthesis of amino acids.
Triplets of bases are used to make different amino acids. DNA could create 43 or 64 possible triplet combinations.
These triplets are called codons and they are the way information is encoded in DNA and RNA
Example: CGG, AGA, CCC
the genetic code
A combination of 3 bases (triplet) forms one codon.
The Genetic Code represents mRNA triplet codons
The Genetic Code is redundant: 64 possible triplet codons for 20 amino acids.
The Genetic Code is universal: All organisms use the same code.
One Start Codon – AUG
3 Stop Codons – UAA, UAG, UGA
60 Codons for 19 amino acids
what is the rule called that dicatates what nitrogenous base binds to what?
something rule lol look it upo
bfe
The first steps in protein synthesis are compartmentalized within the nucleus
Transcription occurs in the nucleus: DNA mRNA
Translation occurs in the cytosol: mRNA Protein
protein synthesis:gene activation
DNA containing a gene must be activated so that its code can be read.
Constitutively active genes are continuously being read and converted to RNA. These code for proteins that are essential to ongoing cell functions.
Other genes are regulated: that is, their activity can be turned on (induced) or turned off (repressed) by regulatory proteins.
transcription.
Transcription = mRNA synthesis. The process by which a strand of RNA is produced against a template of DNA.
1. Regulatory proteins called transcription factors bind to the DNA and activate a region that precedes the gene called the Promoter.
- The active promoter tells RNA Polymerase where to bind to the DNA.
RNA Polymerase – the enzyme responsible for transcription.
- Transcription now begins (see next slide for steps)
- stops at termination sequence
what are the top and bottom strand called in transcription
coding stand is on top and template strand is bottom, rna polymerase only reads the bottom template sttrand
protein synthesis: mRNA processing
Once the completed mRNA transcript is synthesized, it undergoes additional processing before it exits the nucleus.
A 7-methylguanosine cap is added to the start of the pre-mRNA while elongation is still in progress. The 5′ cap protects the mRNA from degradation and assists in ribosome binding during translation.
A poly (A) tail is added to the end of the pre-mRNA once elongation is complete. The poly (A) tail protects the mRNA from degradation, aids in the export of the mature mRNA to the cytoplasm, and is involved in binding proteins involved in initiating translation.
Two forms of additional mRNA processing may take place: Interference and Alternative Splicing
alternative splicing
Genes actually contain DNA segments that encode proteins (exons) and non-coding segments (introns).
In alternative splicing, special enzymes clip introns out of the middle or off the end of the mRNA strand.
Introns must be spliced out so that an mRNA sequence only contains coding sequences (exons).
what is premRNa?
fdas
translation
Protein synthesis requires the cooperation and coordination among all three types of RNA: mRNA, rRNA, and tRNA.
Upon arrival in the cytosol, processed mRNA binds to the ribosomes.
what do transcription factors do
turn on genes, helps rna polymerase bind to promoter
translation
tRNAs read the mRNA codons
Initiated at the AUG start codon that is complimentary to the UAC tRNA anticodon
AUG codes for the amino acid methionine.
Translation ends in the presence of a termination or stop codon on the mRNA (UAA, UAG, UGA).
translation=protein synthesis
polyribosome arrays
assembly line of ribosomes, can be used to make lots of rna
protien synthesis - sorting
Protein Sorting – Specific proteins go from the ribosomes directly to where they are needed in the cell.
Many newly made proteins bind with a signal recognition particle (SRP) as they emerge from a bound ribosome. The SRP binds to the beginning segment of amino acids known as a signal sequence.
The signal sequence tag directs the protein to the cisternae of the RER and allows it to be transported through the organelle membrane.
Once a protein enters the ER lumen, enzymes remove the signal sequence and the protein undergoes modification and packaging.
Proteins that are synthesized in free ribosomes do not have sorting signals and remain in the cytosol.
bound ribosome
bring protien to er
free ribisome
in cytoplasm
