10 - DNA and Protein synthesis Flashcards
Genetic code
The way in which DNA bases code for a sequence of amino acids is the genetic code. It is almost identical to all living organisms and this said to be universal.
Chromosome structure
Long DNA molecules supercoiled around histone proteins
How is DNA found in eukaryotic cells?
In chromosomes
How is DNA found in prokaryote cells?
Circular DNA
Plasmids
Gene
DNA with a base sequence that codes for the amino acid sequence of a polypeptide
Meaning of diploid?
Double the normal number of chromosomes
Meaning of locus?
The position of a gene on a chromosome
How many naturally occurring amino acids are there?
20
Meaning of Triplet?
The sequence of three bases on a DNA molecule that codes for an amino acid - necessary to be able to code for all 20 - gives 64 possible bases
Meaning of degenerate?
The same triplet can code for the same amino acid, so the code is said to be degenerate
‘Stop’ triplets?
3 degenerate triplets in a row
Non overlapping code?
The sequence of triplets is read sequentially and each three bases in a triplet will only be part of coding for 1 amino acid.
Sense strand?
The template strand on a helix of DNA that actually codes for a protein.
Meaning of genome?
The complete set of genes in a cell
‘Junk DNA’
The 98% of DNA that does not code for amino acids - do actually have functions - still researching
Definition of allele?
A different form of a gene
Introns and exons?
The sections of a gene that code for amino acid sequences in the final protein are called exons.
Sections of a gene that do not code for the amino sequence that make up the final protein are called introns.
Proteonme?
The complete set of proteins that are coded for by an organisms DNA
Function of RNA?
DNA kept in nucleus to protect. The genetic information is passed onto mRNA that passes through the pores to the RER and ribsomes to manufacture proteins.
Transcription
The formation of mRNA from the coded information in DNA
- RNA helicase unzips DNA
- Hydrogen bonds broken
- RNA nucleotides bind to DNA bases by complimentary base pairing
- RNA polymerase links RNA nucleotides together forming phosphodiester bonds
- RNA polymerase moves along the sense strand producing a single stranded molecule of mRNA
- Release of mRNA
- mRNA leaves nucleus through nuclear pores
- mRNA is a ‘mirror image’ of DNA
What is a codon?
A sequence of three bases on a mRNA molecule coding for one amino acid
tRNA structure
Upside down cross (clover leaf) with circular ends except for top
amino acid attachment site at top
Single stranded
Hydrogen bonds between
Three unpaired bases making up anticodon on circular ends
Translation
The transfer of the genetic information from mRNA to assemble polypeptides
- mRNA attaches to ribosome at one end
- tRNA, carrying its complimentary amino acid, with complementary bases to first condon binds at its anticodon forming hydrogen bonds
- Another tRNA with its complimentary amino acid binds to the second mRNA codon at its anticodon, forming hydrogen bonds
- The two amino acids are then close and form a peptide bond using ATP
- The ribosome moves along the mRNA molecule
- The first tRNA leaves the mRNA molecule without its amino acid
- The process continues and the polypeptide grows
Anticodon
Three unaired bases on a tRNA
