Chapter 4 - Protein Synthesis Flashcards
What is the genetic code?
- The specific order of nitrogen bases
- It is read by the cell and produces structural and functional proteins for use by the cell or the organism
- organised into genes and codes for a specific protein
What is gene expression?
Reading one gene at a time. It is the process of using one genetic code to synthesise specific proteins.
How are genes bundled together in prokaryotic cells and eukaryotic cells?
Prokaryotic cells - single circular chromosome
Eukaryotic cell - multiple linear chromosome
What are the 3 stages of gene expression/protein synthesis?
- Transcription
- mRNA processing
- Translation
What is transcription?
the process of synthesising a strand of mRNA that is complementary to the DNA base sequence of the gene being read
(makes a copy of a specific gene)
Where does trandcription occur?
inside the nucleus before the mRNA leaves the nucleus
What is the promoter region?
- Indicates the location on chromosome where gene starts
- not transcribed
What is the template strand?
- Strand of the DNA that is transcribed
- All thymine bases will be replaced with uracil
What are the 3 stages of transcription?
- Initiation
- Elongation
- Termination
What is transcription initiation?
- Transcription factors (proteins) bind to the promoter region. This helps RNA polymerase bind to the DNA
- RNA polymerase unwinds the DNA by breaking hydrogen bonds
What is transcription elongation?
- RNA polymerase adds complementary nucleotides to the DNA
- Occurs from 5’ to 3’ direction
What is transcription termination?
- RNA polymerase is released
- 2 strands of the DNA reanneal
- Single strand of the RNA peels off the DNA
- the RNA becomes the primary RNA transcript
What is mRNA processing?
The primary RNA transcript is processed in the nucleus. It is modified in three ways before it leaves the nucleus.
What are the 3 ways the RNA is modified in?
- Caps and Tails
- Splicing the gene
- Reading the genetic code
What is caps and tails?
5’ cap - a modified guanine nucleotide is added to 5’ end.
Poly-A tail - once the whole transcript has peeled f=off the DNA, 50-250 adenine nucleotides are added to 3’ end of RNA
What types of sequence is the gene made up from?
Introns and exons
What are introns?
non-coding regions that do not contribute to building proteins
What are exons?
it is made up of coding sequences. genetic code within exons builds polypeptide.
What is splicing the gene?
A complex of proteins and RNA molecules cut out all introns and stick the exons back together into a single mRNA sequence
What is the reading the genetic code?
- reading the gene in sets of three bases.
Triplet codes - codons (codes for a specific amino acid)
What are stop codons?
Found at the end of the mRNA sequence
UAA, UAG, UGA
What are start codons?
AUG - codes for methionin (MET)
What happens before translation?
Mature mRNA moves out of the nucleus and into the cytoplasm
What is translation?
The process of building a polypeptide chain using the mRNA as instructions
Where does translation occur?
Occurs in the ribosome
What are ribosomes made from
small and large subunit made from proteins and rRNA
What are the 3 stages of translation?
- Initiation
- Elongation
- Termination
What is translation initiation?
- Small ribosomal subunit binds to 5’ of mRNA and moves to start codon
- A tRNA binds to mRNA
- Large ribosomal subunit attaches to the complex
What is translation elongation?
- A tRNA molecules with an inticodon complementary to the next mRNA codon enters ribosome
- Each tRNA carries the amino acid coded for by the codon
- The two amino acids bond together and the first tRNA molecule is released to fetch more amino acid molecules
- mRNA moves through ribosome
What is translation termination?
- Elongation continues until the stop codon moves through the chromosome
- The polypeptide chain is released from the ribosome since the tRNA has a complementary anticodon
What is an anticodon?
The triplet code found on tRNA that is complementary to mRNA sequence
What is the coding region?
The section of the gene that is used to build the polypeptide chain
What is a codon?
Three RNA bases in a row that code for a specific amino acid
