1.3 RNA, Transcription & Translation Flashcards
What is a genotype determined by
The sequence of DNA bases in its genes
What is a phenotype determined by
The proteins that are synthesised when the genes are expressed
What are proteins made up of
Amino acids
What does the sequence of amino acids determine
The structure and function of the protein
What determines the sequence of amino acids
The order of DNA bases
What codes for each amino acid
The order of DNA bases
What is a gene
A section of DNA that codes for a particular protein
What happens to genes during differentiation
Only a fraction of genes are expressed the other genes are switched off
What influences which genes are expressed
The intra and extra cellular environmental factors eg diet, stress and activity levels
What is gene expression controlled by
The regulation of transcription and translation
What is RNA composed of
A phosphate, a ribose sugar and a base
What are the bases in RNA
Adenine, uracil, guanine and cytosine
What are the types of RNA
mRNA, rRNA and tRNA
What is the function of mRNA
To carry a complementary copy of the DNA code from the nucleus to the ribosome
What is the function of rRNA
To combine with proteins to form the ribosome
What is the function of tRNA
Each tRNA carries a specific amino acid to a ribosome to build proteins
How many strands does RNA have
One - it is single stranded
What is transcription
The first stage of protein synthesis
What is made during transcription
A complementary copy of the relevant section of DNA (mRNA)
What happens during the first stage of transcription
Transcription of the gene begins at the promoter region ( a triplet of bases called a start codon )
What happens in the second stage of transcription
Enzyme RNA polymerase attaches to the promoter region
What happens during the third stage of transcription
The DNA unwinds and unzips and the hydrogen bond between bases causing the two strands to separate
What happens in the fourth stage of transcription
Free RNA nucleotides line up against their complementary base on the coding DNA strand. RNA polymerase adds the nucleotides to the 3’end of the forming mRNA strand
What happens in the fifth stage of transcription
Weak hydrogen bonds form between the base pairs and strong sugar phosphate bonds form between the adjacent RNA nucleotides forming a strand of mRNA called the primary transcript. The process stops when the terminator region is reached
Before leaving the nucleus what has to happen to mRNA
It has to be modified to form the mature transcript
What does modification of the primary transcript involve
Removing any non coding sections called introns leaving behind the coding regions called exons
What is RNA splicing
The process which joins together the remaining exons to form a continuous sequence called the mature transcript
What then happens to the mature transcript after splicing
It leaving the nucleus and travels to the ribosome reading for translation
What is translation
The second stage of protein synthesis
What is the mRNA used for in translation
To synthesise a polypeptide chain in the ribosome
How many codons code for 1 amino acid
1 codon
Where is tRNA found
The cytoplasm
What is tRNA made up of
A single chain of RNA nucleotides
What is the structure of tRNA like
Folded into a 3D structure, held together by hydrogen bonds between bases
What is the triplet of bases of tRNA called
Anticodon
What does the anticodon determine
the specific amino acid that tRNA will carry
What is the first stage of translation
The ribosome binds to the 5’ end of the mRNA at the start codon
What is the second stage of translation
A tRNA carrying an amino acid lines up against its complementary codon on mRNA. Hydrogen bonds form between the codon of mRNA and the anticodon of tRNA
What is the third stage of translation
Another tRNA carrying a specific amino acid lines it’s anticodon against its complementary codon on mRNA. Hydrogen bonds form between the bases.
What is the fourth stage of translation
A peptide bond forms between the first two amino acids
What is the fifth stage of translation
The ribosome then moves along one codon exposing the next codon to an anticodon
What is the sixth stage of translation
The process is repeated many times until the stop codon is reached and a complete polypeptide chain is translated.
What does a start codon do
It initiates translation on mRNA
What does a stop codon do
Signifies that the polypeptide chain is complete
What are produced from the same primary transcript
Different mRNA molecules
How can the same gene be used to make several different proteins
Alternative RNA splicing and Post translational modification
What happens in alternative RNA splicing
Different RNA segments can be treated as introns and the resulting exons can be spliced together in different orders to form different proteins from the same original gene
What is post translational modification
When the polypeptide chain can be modified after it has been formed in translation by one of two methods
What are the two methods of post translational modifications
Cleavage and molecular addition
What is cleavage
When the single polypeptide chain can be cut and or combined with polypeptide chains to form different protein structures
What is molecular addition
When other molecules are added to the polypeptide chain such as carbohydrates and phosphate groups
