gene expression 1.3 Flashcards
gene expression
involves transcription and translation of DNA sequences
what’s the first step of protein synthesis
transcription which is when the gene on the DNA strand that codes for the protein is copied into a molecule of mRNA
what is the second step of protein synthesis
translation which takes place at the ribosome when mRNA code is used to make the protein
which structures are involved in transcription
mRNA
which structures are involved in translation
tRNA and rRNA
how many strands does RNA have
RNA is a single stranded molecule
what is RNA composed of
RNA nucleotides
what does each RNA nucleotide consist of
a ribose sugar, a phosphate group and a base
what are the RNA nucleotide bases
adenine, uracil, guanine and cytosine
messenger RNA function
carry a copy of the DNA code from the nucleus to the ribosome
what is each triplet in mRNA called
a codon which codes for a specific amino acid
transfer RNA structure
tRNA folds due to the complementary base pairings A-U and G-C
transfer RNA function
carries a specific amino acid to the ribosome during translation
what does tRNA molecules contain
they contain an anticodon (an exposed triplet of bases) at one end and an attachment site for a specific amino acid at the other end
ribosomal RNA function
to bring tRNA molecules bearings amino acids into contact with the mRNA molecule during translation
ribosome structure
made up of rRNA and protein
transcription function
the synthesis of a molecule of mRNA from a section of DNA (a gene) by the enzyme RNA polymerase
process of transcription
-RNA polymerase moves along the DNA strand unwinding the double helix and breaking the hydrogen bond between base pairs and separating the two DNA strands
-RNA polymerase synthesises the primary transcript of mRNA using RNA nucleotides by complementary base pairings
RNA splicing function
to form the mature mRNA transcript
process of RNA splicing
-the introns of the primary transcript are non coding regions and are removed from the strand
-the exons are coding regions and are joined together to form the mature transcript of mRNA
-the order of exons is unchanged during splicing
translation function
to translate mRNA into a polypeptide at a ribosome
process of translation
-translation begins at a start codon and ends at a stop codon
-tRNA anticodons bond to mRNA codons by complementary base pairings
-this translates the mRNA genetic code into a sequence of amino acids
-the amino acids are held together by peptide bonds
-each tRNA then leaves the ribosome as the polypeptide is formed and is free to pick up another amino acid
protein structure
proteins are made up of chains of amino acids of which there are 20 different types
the length of a protein
can vary from a thousand to just a few
