Biological molecules - The Role Of Genes Flashcards
Define a gene
A sequence of nucleotide bases which corresponds to a sequence of amino acids
What is a sequence of 3 bases called
A triplet (codon in mRNA)
What do triplets correspond to
A specific amino acid
What happens as codons are read
Polypeptides are made and these form the primary structure of all proteins
How can genes be switched on or off
In response to signals that reach the cell and nucleus
why must a copy of each gene be transcribed into a length of mRNA
DNA is found in chromosomes and cannot pass out through the nuclear pores
where are proteins synthesised
on ribosomes
what happens to mRNA after it is made
passes out of the nucleus and moves to a ribosome where it is translated to make a protein
what are the characteristics of the genetic code
- universal
- triplet
- degenerate
- non-overlapping
what does it mean that the genetic code is degenerate
for all amino acids (except two) there is more than one base triplet
how is RNA similar to DNA
- polynucleotide strand with a sugar-phosphate backbone
- the nucleotides contain one of four bases
how is RNA different to DNA
- ribose sugar
- single stranded polynucleotide
- uracil replaces thymine
what are the three forms of RNA
- mRNA
- rRNA
- tRNA
what is mRNA
messenger RNA is made as a complementary strand to a section of DNA. transfers information to ribosome
what is rRNA
ribosomal RNA is found in ribosomes. provides the site for protein assembly in the ribosome
what is tRNA
transfer RNA carries amino acids to ribosomes
Where is mRNA formed
In the nucleus
What is the first step of transcription
A section of the DNA unzips (H bonds between base pairs break)
What is the second step of transcription
Activated RNA nucleotides form H bonds with exposed complementary bases on template strand in the nucleolus
What is the third step of transcription
The enzyme RNA polymerase checks for mistakes and catalyses the formation of phosphodiester bonds between the mRNA nucleotides forming the sugar phosphate backbone
What provides the energy for the bonding of adjacent nucleotides
The release of the two extra phosphate groups provides the energy for bonding the adjacent nucleotides
What is the fourth step of transcription
At a stop triplet the mRNA breaks off and leaves the nucleus via a nuclear pore
What is the fifth step of transcription
In the cytoplasm the mRNA strand attaches to a ribosome
Where are ribosomes made and what are they made of
Made in the nucleolus
Made of ribosomal RNA and protein as two subunits
Describe ribosomes role in protein synthesis related to its structure
Ribosomes move into the cytoplasm through pores in the nuclear envelope. The two subunits come together to form the ribosome. It has a groove in between where the mRNA is translated into a protein
Where is tRNA made
Made in the nucleus and passes into the cytoplasm
Describe the structure of tRNA
- a single stranded polynucleotide folded into three hairpin loops
- one free end of unpaired bases joins to a specific amino acid
- at the opposite end there are three unpaired bases called the anticodon
- this briefly joins to the complementary codon on the mRNA
What are the triplets of nucleotide bases on mRNA known as
Codons
What is the first step of translation
mRNA attaches to ribosomes, either on the RER or free in the cytoplasm
tRNA is in the cytoplasm and has a specific amino acid attached to it
What is the second step of translation
tRNA anticodon joins onto the mRNA codon
What is the third step of translation
A second tRNA with its specific amino acid joins to the second codon with its complementary anticodon
what is the fourth step of translation
a peptide bond forms between the two amino acids and the ribosome moves along. the bond formation requires energy, in the form of ATP.
this continues down the length of the mRNA strand until it reaches a stop codon
what is the fifth step of translation
the polypeptide chain can now be arranged into its secondary and tertiary structure
what happens to mRNA after translation
after the polypeptide has been assembled, the mRNA can be re used or breaks down and its component pieces recycled.
what kinds of mutations could occur
replacement, insertion, deletion
what is an insertion an example of
a point mutation
describe point mutations
random and spontaneous
are mutations always harmful and why
no, lots of genes have their sequences changed and this is what creates alleles
