Topic 4A: DNA, RNA and Protein Synthesis Flashcards
How does Eurkaryotic cells store DNA?
As linear DNA molecules that are threadlike structures each made up of one long molecule of DNA and associated with histone proteins
What do histone proteins do
Helps support the DNA the DNA is then coiled up very tightly to make a compact compound
In eukaryotes what has its own DNA
mitochondria and chloroplasts, similar to prokaryotes DNA (circular and shorted)
What is DNA like it prokaryotes
Shorter and circular, not wound around proteins condenses a to fit into the cells by super coiling
What does DNA contain
Genes
What is a gene
Sequence of DNA bases that codes for either a polypeptide or functional RNA
What determines order of amino acids of a polypeptide
Order of bases in a gene, different polypeptides have different number and order of amino acids
What is each amino acids coded by
For by 3 bases in a gene called triplet or codon
How do you make polypeptide
DNA if first copied into messenger RNA, this is the first stage of protein synthesis
Genes that don’t code for polypeptide codes for what?
Functional RNA
What is functional RNA
RNA molecules other than mRNA which preform special tasks during protein synthesis
Give 2 examples of functional RNA
tRNA and rRNA
What is a genome
Full set of genes in a cell
What is proteome
Full range of proteins that the cell is able to produce
What are introns
Non-coding regions of DNA
When are introns removed
During protein synthesis
Why are introns removed during protein synthesis
So they don’t affect amino acid order
What type of DNA doesn’t contain introns
Prokaryotic
What are introns
Coding regions of DNA
What are regions of multiple repeats
Sequence that repeats over and over again, they don’t code for AA either they are called non-coding multiple repeats
What’s an allele
A different version of a gene
How do chromosomes pair
In homologous pairs
What are chromosomes like in homologous pairs
Same size and have the same genes, however they can have different alleles although alleles coding for the same will be found at the same fixed position (locus) on each chromosome
What is protein synthesis
Production of proteins from the information contained within a cells DNA
What’s the 2 stages of protein synthesis
Transcription and Translation
What’s the structure of mRNA
Single polynucleotide strand
Where is mRNA made and what does it do
Made during transcription it carries the genetic code from the DNA to ribosomes where it’s used to make a protein during translation
What is tRNA involved in
Translation
What does tRNA do
Carries AA that are used to make proteins to the ribosomes
What’s the structure of tRNA
Single polynucleotide strand that’s folded into a clover shape, hydrogen bonds between specific base pairs hold the molecule in this shape
Every tRNA has a specific sequence of three bases at one end called an anticodon
It has an AA binding site at the other end
What is step 1 of transcription
RNA polymerase attaches to the DNA, transcription starts when RNA polymerase attaches to the DNA double helix at the beginning of a gene
The hydrogen bonds between the two DNA strands break separating the strands and the DNA molecule uncoils exposing some of the bases
One is used to make a template
What is step 2 of transcription
The RNA polymerase lines up free RNA nucleotides alongside exposes bases on the template stand
The free bases are attracted to the exposed bases, specific complementary base pairing means that mRNA strand is a complementary copy
Except T is replaced by U
Once paired RNA polymerase joins them up forming mRNA molecule
What is step 3 of transcription
RNA polymerase moves along the DNA, separating the stands and assembling the mRNA stand
Hydrogen bonds between uncoiled strands reform once RNA polymerase has passed over them
Coiling back into a double-helix
What is step 4 of transcription
When RNA polymerase reaches a particular sequence of DNA called stop signal it stops making the mRNA and detaches from DNA
mRNA moves out of the nucleus through a nuclear pore and attaches to a ribosome in cytoplasm where translation occurs
What is meant by editing mRNA
In eukaryotes introns and exons are copied into the DNA mRNA containing both is called pre-mRNA, a process called splicing occurs where introns are removed and exons are joined together forming mRNA
Taking place in nucleus, RNA leaves nucleus for translation
What’s step 1 of translation
mRNA attaches itself to a ribosomes and tRNA molecules carry AA to it, ATP provides the energy needed for the bond between AA and tRNA molecule to form
What is step 2 of translation
A tRNA molecule (carrying AA) with an anti-codon that’s complementary to the first codon on the mRNA attaches itself to the mRNA by complementary base pairing
A second tRNA molecule attaches itself to the next codon on the mRNA in the same way
What is step 3 of translation
The two AA attaches to the tRNA molecules are joined by a peptide bond
The first tRNA molecule moves away, leaving its AA behind
What is step 4 of translation
Third tRNA molecule binds to the next codon on the mRNA
It’s AA binds to the first two and the second tRNA molecule moves away
This process continues producing a chain of linked AA until there’s a stop signal on the mRNA molecule
Polypeptide chain then moves away from the ribosomes and translation is complete
What is the genetic code
Sequence of base triplets in mRNA which code for specific AA
In the genetic code each base is read in sequence, separate from triplet before it and after it
What are the 3 main features of the genetic code (explained)
Non-overlapping: Base triplets don’t share their bases
Degenerate: there’s more possible combinations of triplets than there are AA meaning some AA are coded for by different combinations
Universal: same specific base triplets code for the same AA in all living things
