Protein Synthesis Flashcards
RNA Nitrogenous bases
Adenine
Uracil
Guanine
Cytosine
RNA
When the nucleotides of RNA join, the ribose of one nucleotide attaches to the phosphate group of another to form a long, single-stranded molecule. Unlike in DNA which forms double-stranded molecules, the RNA bases, therefore, can occur in any number and ratio.
Messenger or mRNA
mRNA is formed in the nucleus but then enters the cytoplasm where it attaches to ribosomes. It is a long single-stranded molecule formed by copying particular segments of DNA (genes). mRNA carries the genetic code to the ribosomes in the cytoplasm where proteins get manufactured.
Transfer or tRNA
tRNA is found freely in the cytoplasm of the cell. It is made of a single strand that folds back on itself and forms loops. There are three important exposed bases called the anticodon on one of the loops. tRNA picks up amino acids (the building blocks of proteins) and takes them to the ribosomes where proteins get manufactured.
Ribosomal or rRNA
rRNA is found in the ribosomes in the cytoplasm of the cell. It is a single strand that folds to form the structure of the ribosome. The ribosome is the site where proteins are manufactured.
Protein Syntheisis
The process by which proteins are made is called protein synthesis. Proteins are made by bonding various amino acids that are present in the cytoplasm of cells. There are 20 different amino acids, and they combine in a large variety of combinations.
What are amino acids joined by?
Amino acids are joined by peptide bonds. The smallest protein contains 50 amino acids bonded together, generally, proteins consist of more than 300 amino acids.
Genes
The genes found in the DNA hold the code for particular proteins to be formed. Three consecutive nitrogenous bases in a gene are called base triplets. The sequence of base triplets in a gene forms codons on mRNA which ultimately determines which amino acids will be placed in sequence, building a particular protein.
Transcription
The double helix DNA unwinds.
Double-stranded DNA unzips when the hydrogen bonds break (at the site of a particular gene) to form two separate strands
One strand of DNA is used as a template
to form mRNA
using free RNA nucleotides from the nucleoplasm (Uracil in place of thymine in RNA).
A single-stranded mRNA, complementary to the DNA, is formed (e.g. base triplet ACC on DNA will be a codon UGG).
mRNA now has the coded message for protein synthesis (and it moves away from the DNA strand)
Translation
mRNA moves from the nucleus to the cytoplasm and attaches to the ribosome.
Each codon now provides the order for linking amino acids to form a protein.
Each tRNA carries a specific amino acid.
When the anticodon on the tRNA matches the codon on the mRNA then tRNA brings the required amino acid to the ribosome. The tRNA then goes off to pick up another amino acid.
Amino acids at the ribosome become attached by peptide bonds to form the required protein.
