DNA, genes and protein synthesis Flashcards
(18 cards)
What is a gene
A section of DNA that contains the coded information for making polypeptides and functional RNA. It is located on the LOCUS of a DNA molecule.
What does a gene code for
-amino acid sequence of a polypeptide
- functional RNA, including ribosomal RNA and transfer RNAs.
One DNA molecule carries many genes
Features of the genetic code
- Degenerate- a few amino acids are coded for by only a single triplet, the remaining amino acids are coded for by between 2 and 6 triplets each. Most amino acids are coded for by more than one triplet
-Non overlapping. A triplet is always read in one particular direction along the DNA strand. It starts with methionine (the starting triplet) that is later removed from the polypeptide chain. Base sequence is only read once
-Universal. Each triplet codes for the same amino acid in all organisms. This is indirect evidence for evolution.
Extrons VS introns
Much of DNA in eukaryotes doesnt code for polypeptides. Between genes there are non-coding sequences made up of multiple repeats of base sequences. Even within genes only certain sequences code for amino acids. Coding sequences are called extrons. Extrons are seperated within the gene by further non-coding sequences called introns. Some genes code for ribosomal RNA and transfer RNAs
Homologous chromosome
Two chromosomes that carry the same gene but not necessarily the same alleles of the gene
Allele
Alternative form of a gene. Each individual inherits one allele from each of its parents
Prokaryotic VS eukaryotic DNA
Prokaryotic and mitrcondrial/ chlorplast DNA= short, circular, not associated with histones
Eukaryotic= long, linear and associated with histones
locus
location/position of a gene on a chromosone
difference between mRNA and tRNA
mRNA- larger, single helix, greater variety of types
tRNA- smaller, clover leaf shape, less variety of types, contains hydrogen bonds between the bases
proteome
full range of proteins produced by the genome
complete proteome- proteins produced by a certain type of cell under a set of given conditions
where does polypeptide chain go after translation
- then move through cytoplasm to golgi apparatus, there vesicles will process proteins. The formed/ folded proteins will then leave the cell via exocytosis to be used
molecular differences between DNA and RNA
- RNA smaller than DNA
- RNA is single strand and DNA is a double helix
- sugar in RNA is ribose while the sugar in DNA is deoxyribose
- in RNA the base uracil replaces the base thymine found in DNA
when does translation stop
when a stop code is reached
- RNA polymerase will add nucleotides one at a time until this happens, allowing the DNA strand to reform behind it and therefore reducing the number of DNA bases that are actually exposed
what do amino acids joining require
ATP!!!!!
…
- translation only occurs on one strand of the polypeptide chain after the DNA molecule has been unzipped, NOT BOTH
- this strand is called the template strand or transcribed strand
- the mRNA is made complementary to the template strand, so will be pretty much identical to the coding strand, apart from the swapping of uracil
alternative splicing
The exons of genes can be spliced in many different ways to produce different mature mRNA molecules through alternative splicing
- this means that a single eukaryotic gene can code for more than one polypeptide chain
- this is part of the reason why the proteome is much bigger than the genome
splicing occurs before the pre-mRNA molecule exits the nucleus
what is a ribosome made up of
ribosomal RNA and protein/polypeptide
sense strand
Sense strand, or coding strand, is the strand of DNA that has the same base sequence as the mRNA, except with Uracil instead of thymine.
The sense strand is the one that carries the translatable code in the 5’ TO 3’ direction, while the template strand is used during transcription to build the mRNA
