3. Protein Synthesis Flashcards
What is a gene?
A length of DNA that codes for the assembly of a protein or RNA molecule. A single gene contains hundreds to millions of bases.
- Chromosomes contain hundreds to thousands of different genes.
- Genes in eukaryotic cells contain exons and introns.
What are introns and exons?
Introns are segments of a gene that do not code for the synthesis of a protein. Exons are segments of a gene that code for the synthesis of a protein.
What is RNA Splicing?
In transcription the entire gene (exons and introns) is copied into a messenger RNA (mRNA) molecule. This molecule is called pre-mRNA and needs to be modified. RNA splicing is the removal of introns from pre-mRNA to form mature – mRNA. The process is carried out by a protein-RNA complex called spliceosome. Mature-mRNA contains only exons and are translated into proteins
What is transcription and its process?
Transcription is when the genetic code is copied from the gene (DNA) to messenger RNA (mRNA). It is the first stage of protein synthesis.
1. An enzyme (Helicase or RNA polymerase) breaks the weak hydrogen bonds between the bases causing the two DNA strands to separate at a specific site.
2. Free RNA nucleotides are attracted to the exposed complementary bases on the template strand of the DNA molecule.
3. An enzyme called RNA polymerase joins the sugar and phosphate groups of adjacent RNA nucleotides creating the backbone of the mRNA molecule. The mRNA strand detaches from the template DNA strand.
4. mRNA is cut by enzymes to remove the introns. Ligase enzymes join the exons together to form a working copy of mRNA that will be translated. mRNA leaves nucleus and travels to ribosome for translation
What is messenger RNA (mRNA)?
Synthesised during transcription, mRNA is the working copy of the gene. It enables a protein to be formed. It has the same sequence as the coding strand of DNA except it has Uracil instead of Thymine. MRNA then travels to the ribosomes
What is Ribosomal RNA (rRNA)?
- Ribosomes consist of a small and large subunit.
- The small subunit reads the mRNA and the large subunit joins the amino acids to form a protein.
- Ribosomes are composed of rRNA (60%) and protein (40%)
- The rRNA functions as an enzyme by catalysing the formation of the protein molecule
What is Transfer RNA (tRNA)?
- A small RNA molecule that transfers amino acids to the ribosome during translation.
- tRNA molecules have an attachment site for a specific amino acid (anticodon) which is complementary to mRNA which has a binding region called a codon.
- Anticodons are a sequence of 3 bases which are complementary to the mRNA codon which codes for the attached amino acid.
What is translation and its process?
Translation is when the protein molecule is assembled using the genetic code on the mRNA. It is the last stage of Protein Synthesis.
1. A mature mRNA molecule attaches to the small ribosomal unit of a ribosome.
2. A tRNA molecule transfers the first amino acid to the ribosome. Hydrogen bonds are formed between the tRNA anticodon and the mRNA codon
3. The mRNA molecule moves so that the next codon is now covered by the ribosome. A second tRNA transfers an amino acid to the ribosome. The large ribosomal unit catalyses a chemical reaction that joins the amino acids together.
4. The process is repeated until a stop codon is reached on the mRNA. The newly synthesized protein molecule then moves to the rough endoplasmic reticulum for modification.
What is a triplet?
3 bases in a gene on DNA coding for an amino acid
What is a codon?
opposing 3 bases on mRNA coding for an amino acid
What is an anticodon?
opposing 3 bases on tRNA that have a specific amino acid attached
What is a template strand?
single strand of DNA from which a single stranded molecule of mRNA is made from in transcription.
What is a CodingStrand?
the strand ofDNA which has the correct sequence to produce a protein, the same as the mRNA strand
