1.3. Gene Expression Flashcards
What are the main differences between DNA and RNA?
RNA has one strand of nucleotides while DNA has two.
The complementary base for adenine in DNA is thymine, but it is uracil in RNA.
The type of sugar present in an RNA nucleotide is ribose sugar while in DNA it is deoxyribose sugar.
What is the function of mRNA (messenger RNA)?
Copies a section of DNA and carries it into the cytoplasm to a protein building molecule called a ribosome.
What is the function of tRNA (transfer RNA)?
Carries the amino acids into position at the ribosome in a process called translation.
What is the function of rRNA (ribosomal RNA)?
The RNA part of the ribosome which aids protein synthesis.
Describe the process of transcription in protein synthesis.
As DNA is too large to leave the nucleus through the pores so a copy is made by producing a similar molecule called mRNA.
It begins when RNA polymerase joins onto the DNA at the promoter region and starts to unzip the DNA. This starts the formation of mRNA which forms according to the base pairing rules. This process continues until the RNA polymerase reaches the terminator region and is released from the DNA strand. The newly formed mRNA then is comprised of two parts, coding sections (exons) and non-coding sections (introns). The introns are removed through a process known as RNA splicing and the mature transcript is formed. The mature mRNA then leaves the cell through the membrane and begins translation.
Describe the process of translation in protein synthesis.
The mRNA attaches itself to the ribosome. tRNA then picks up free amino acids and brings them to the ribosome. Once the start codon is reached the rRNA reads the mRNA and each tRNA anticodon (triplet in tRNA) links with the codon (triplet in mRNA). Each anticodon on tRNA codes for a specific amino acid and peptide bonds link the amino acids into a peptide chain. Hydrogen bonds between the codon and anticodon break and tRNA is released and goes to pick up more amino acids. The ribosome moves along the mRNA strand and the anticodon - codon matching continues until the whole mRNA molecule is completely translated or the stop codon is reached. The peptide chain then is released.
What does “one gene, many proteins” mean?
It refers to the fact that different parts of the immature mRNA molecule being read as introns and exons. Therefore the same primary mRNA can make several mRNA molecules with different triplets so different polypeptides will be produced too.
