DNA and Protein Synthesis Flashcards
Features of DNA in a eukaryotic cell?
Found in the nucleus In a linear shape In the form of chromosomes Wrapped around proteins called histones Long DNA molecule
Features of DNA in a prokaryotic cell?
Found loose in the cytoplasm
In a circular loop form
Shorter DNA molecule
Other than the nucleus where else is DNA found in eukaryotic cells?
Mitochondria
Chloroplasts
How is the mitochondrial and chloroplast DNA thought to have got there?
Endosymbiotic theory
The organelles may have been engulfed and then kept to be used
How is DNA formed into a chromosome?
The DNA double helix is wrapped around histone proteins creating nucleosome fibre
The nucleosome fibre is coiled around to form chromatin fibre
The chromatin fibre is looped in a figure of 8 shape and 6 loops form a rosette
30 rosettes make a coil and there are 10 coils in each chromatid
Why is DNA stored in a chromosome like it is?
So you can have a lot of DNA in a small space
It is easy to separate the DNA without damage
What is a gene?
Part of the length of a DNA molecule that codes for 1 polypeptide
What is different about DNA?
Not all of it codes for proteins
What is DNA made up of?
Introns and exons
What are introns?
Non-coding DNA which can be found between genes in multiple repeats or within a gene
What are exons?
Sequence of bases in a gene that code for a sequence of amino acids in a protein
What is your genome?
The full set of genes in a cell
What is your proteome?
The full range of proteins coded for by the genes
What is your karyotype?
It is the number and appearance of chromosomes in the nucleus of a eukaryotic cell
What is an allele?
Different forms a gene can take
What are some key features of DNA that allows it to code effectively for a polypeptide?
Universal code
1 codon = 1 amino acid
Degenerate code
Non-overlapping
What is a universal code?
DNA is used in virtually all organisms as the material of inheritance
What is a codon?
It is made up of 3 bases
3 bases = 1 codon = 1 amino acid
What is a degenerate code? Use?
The amino acids can be coded for by more than one codon
Combats the substitution mutations in the third base as it has very little affect on the polypeptide being made
How does non-overlapping make DNA effective in production of polypeptides?
Each base in the sequence is read only once
What are the stages of protein synthesis?
Transcription
Translation
Where does transcription take place?
In the nucleus
What is DNA and pre mRNA made up of?
Introns
Exons
What are introns and exons? How to remember?
Exons contain the genetic information that codes for a protein
Introns are sequences that are not used to make the final protein
Introns - In the bin
Exons - Expressed
What happens to convert pre mRNA to mRNA?
Introns are removed and Exons are spliced together
What are the stages of transcription?
DNA that forms the gene is unzipped to form two separate strands using DNA helicase
Free RNA nucleotides aline to their corresponding base pairs on the template strand forming hydrogen bonds
RNA polymerase forms the sugar-phosphate backbone - creating phosphodiester bonds
The pre mRNA is processed with introns removed and exons are spliced together
Then the mRNA will leave the nucleus
What happens between tRNA and amino acids in translation?
The amino acids are activated by combining with the tRNA in the cytoplasm
They combine to a specific amino acid codon catalysed by an enzyme and uses ATP
What happens in translation?
The ribosomes move along the mRNA and ‘reads’ the code
The tRNA molecules with their amino acids attached find their complementary codon in the mRNA
Each ribosome can take 2 tRNA molecules
The amino acids at the top bind forming a peptide bond using ATP in a condensation reaction
Continues until stop codon is reached
What happens when two amino acids have formed a peptide bond in translation?
The first tRNA molecule is released separating from the amino acid and mRNA
It is sent back to the cytoplasm to find more amino acids
When does translation end?
When it reaches a stop codon
Then the ribosome will detach from the mRNA
What is the first amino acid in every translation?
Methionine - AUG
How many ribosomes can you send along the mRNA? Why?
50 travelling behind each other
So you can translate many polypeptides at once
How does protein synthesis occur differently in prokaryotic cells?
Translation occurs in the cytoplasm not nucleus
RNA polymerase copies the DNA in a circular strand not linear
Not introns to be removed therefore no pre mRNA
Where does transcription occur in eukaryotic and prokaryotic cells?
In the cytoplasm
