Chapter 8 - DNA genes and protein synhesis Flashcards
what are the two stages of protein synthesis
- transcription
- translation
what happens in transcription
1) DNA helicase unwinds a segment of the DNA by disrupting the h bonds to expose the bases to act as a template strand
2) only one strand of DNA acts as a template
3) free RNA nucleotides in the nucleus pairs with the exposed base pairs on the template strand by complimentary bae pairing
4) the RNA polymerase binds to the promotor region (start of the gene) and joins nucleotides together by phosphodiester bonds to form a single strand of pre MRNA via condensation reactions
5) The DNA recloses behind the RNA polymerase as it moves a long the gene and once the RNA polymerase reaches the terminator region (end of the gene) of the gene it detaches and the pre mRNA is then complete
6) the pre mRNA the is modified to become mRNA that is ready to leave the nucleus and take part in translation
advantages of the structure of mRNA
shorter than DNA so is able to carry the genetic code to the ribosome in the cytoplasm to enable the protein to be made
what is the aim of transcription
to make a RNA copy of a gene’s DNA sequence
how is the pre MRNA modified
- the introns are SPLICED OUT (removed) and the exons are SPLICED TOGETHER (joined) by a protein called a splicesome in the pre mRNA to form mature mRNA
process of translation
1) once the modified mRNA has left the nucleusand the small unit of the ribosome attaches to the start codon (the 3’ end)
2) the tRNA molecule brings a specific amino acid and binds its complementary anticodon to the start codon of the mRNA and is held in place by the hydrogen bonds between the complementry base pairs on the mRNA and tRNA
3) the large subunit of the protein then binds to the ribosome and a second tRNA molecule with a complimentary anticodon is able to bind to the next mRNA codon
4) the two specfic amino acids that are attached to the tRNA molecules are joined by a peptide bond and is catalysed by an enzyme via a condensation reaction using energy from hydrolysis of ATP
5)the ribosome moves along the mRNA molecule by 3 base pairs and the first tRNA molecule is released causing the second tRNA molecule to be in same position of the first tRNA molecule in the ribosome but with a dipeptide
6) This continues until the ribosome reaches the stop codon at the end of the mRNA molecule, the stop codon does not code for an amino acid, so the ribosome detaches and translation ends
7) the polypeptide chain is now created and will enter the Golgi for modifiction
how is the polypeptide chain made into a protein
it is coiled and folded into its secondary structure and the secondary structures folded to make tertiary structure, the different polypetide chains with prosthetic groups (non proteins) link to form a quaternary structure forming a protein
codon
a sequence of 3 bases on a mRNA molecule that codes for one amino acid
genome
a complete set of genes in a cell
complete proteome
full set of proteins the genome can produce
proteome
the proteins produced by a specific cell under certain conditions
RNA
a polymer of a nucleotide formed of ribose a nitrogenous base and a phosphate group
what are the nitrogenous bases for RNA
adenine guanine cytosine and uracil
characteristics of RNA
- it is single stranded
- has a pentose sugar called ribose
- each RNA nucleotide has 4 bases
function of RNA
- it copies and transfers the genetic code from the DNA in the nucleus to the ribosomes.
- Some RNA is also combined with the proteins to create ribosomes
what is mRNA
a single stranded copy of a gene from DNA arranged in a single helix
three types of RNA
mRNA - (messenger RNA)
tRNA - (transfer RNA)
rRNA - (ribosomal RNA)
why cant the DNA leave the cell and be used for translation
as the DNA is too large to leave the nucleus and would be at risk of being damaged by enzymes therefore destroying genetic code
why is mRNA used in translation
- mRNA is much shorter as it is only the length of one gene and so can leave the nucleus
- mRNA is short-lived since it is only needed temporarily so by the time the enzyme could break it down it would have already carried out its function
where is tRNA found
in the cytoplasm
where is mRNA made
in the nucleus
structure of tRNA
it is single-stranded but folded to create a clover leaf shape which is held by hydrogen bonds
function of tRNA
- to attach to one of the 20 amino acids and transfer the amino acid to mRNA which is attached to the ribosome to create the polypeptide chain
how do specific amino acids attach to specific tRNA molecules
by complementary base pairing of the 3 bases at the extended 3’ end of the tRNA
how does the tRNA bind to the mRNA
the tRNA contains anticodon which are complementary to the codon on mRNA (anticodons do not bind to the amino acids)
function of rRNA
makes up the bulk of ribosomes
how to determine which tRNA binds to which amino acid
1) you would look at the code for the anticodon
2) then you would determine the complimentary codon of the anticodon
3) then using that complimentary code use the genetic table to find the amino acid attached
differences between the DNA and RNA MONOMERS
- DNA contains the base thymine whereas RNA contains uracil
- DNA contains the pentose sugar deoxyribose whereas RNA contains the pentose sugar ribose
key features of the genetic code
1) degenerate
2) universal
3) non overlapping
what is the start codon
the 3 bases as the start of every gene (AUG) which initiates translation and codes for the amino acid methionine
what is the stop codon
the 3 bases at the end of every gene that does not code for an amino acid, so marks the end on the polypeptide chain and cause the ribosome to detach stopping translation
how many different amino acids are there
20
mathematical proof that 3 bases code for the 20 amino acids
4^n
(4 because there are 4 different bases and the n represent the number of bases that make up your code)
- if 1 base coded for one amino acid (4^1) this will only allow for 4 amino acids to be coded for which is insufficient as there are 20 amino acids
if 2 base coded for one amino acid (4^2) this will only allow for 16 amino acids to be coded for which is insufficient as there are 20 amino acids
- if 3 base coded for one amino acid (4^3) this will only allow for 64 amino acids to be coded for which is sufficient as there are 20 amino acids
what is degenerate code
more than one triplet coding for the same amino acid
what causes degenerate coding
as there are 64 combinations to code for 20 amino acids so it results each amino acid to be coded by more than one triplet of bases
the advantage of degenerate code
as if a mutation occurs even though the triplet bases will be different it may still code for the same amino acid so the mutation will have no effect
what is universal code
The same codon always codes for the same amino acid
advantage if universal code
makes genetic engineering possible
what is non overlapping code
each base is only one part of a triplet codon
advantage of non overlapping code
if point mutation occurs it will only affect one codon and therefore one amino acid
what are introns
sections of DNA that do not code for amino acids
where are introns found
in eukaryotic DNA but not prokaryotic DNA
what are exons
base sequence coding for sequence of amino acids
differences between genome and proteome
- the genome is an organism’s complete set of DNA in one cell whereas the proteome is the full range of proteins in one cell
- the genome should never change whereas the proteome of the cell is constantly changing depending on which proteins are currently needed
what is a gene
a section of DNA that contains a code for making a polypeptide and functional RNA
what is the locus
the location of a particular gene on a chromosome
what is an allele
an alternative form of the same gene
what are homologous pairs
pairs of matching chromosomes, with the exact same size and the exact same genes but may have different alleles
how is DNA stored in eukaryotic cells
- DNA is stored as chromosomes inside the nucleus
- The DNA is coiled by it tightly winding around proteins called histones (this complex is called nucleosome)
how is DNA stored in prokaryotic cells
- the DNA is stored inside a single looped chromosomes that are not wound around histones but supercoils to fit inside the cell instead
which two organelles have their own DNA
- chloroplast
- mitochondria
how is the DNA in mitochondria and chloroplast is similar to the ones in prokaryotic cells
- The DNA is short
- The DNA is circular
- The DNA is not histone bound
differences between prokaryotic and eukaryotic DNA
pro has short circular dna whilst eu has long linear DNA
pro dna is not histone bound whilst eu is
pro does not have any junk dna or introns whilst eu does
compare and contrast tRNA to mRNA
sim
both single polynucleotide strand
difference
- tRNA is folded into a clover leaf shape wheras mRNA is linear
- tRNA has hydrogen bonds between base pairs and mRNA doesnt
- tRNA has anticodons whereas mRNA has codons
- tRNA has an amino acid binding site whereas mRNA doesnt
-tRNA is shorter fixed in length whereas mRNA is longer variable length
similarities between dna in eukaryotic and prokaryotic
- nucleotides are joined by phosphodiester bonds
- nucleotide structure is identical
- dna in mitochondria and chloroplast is similar to DNA in prokaryotes
describe how a gene is a code for the production of a polypeptide
- base sequence in triplets determine the order of amino acid sequence in a polypeptide
Describe how a gene is a code for the production of a polypeptide. Do not include information about transcription or translation in your answer.
- Base nucleotide sequence
- In triplets
- Determines order of amino acid sequence
Describe the role of a ribosome in the production of a polypeptide. Do not include
transcription in your answer
- mRNA binds to ribosome;
- Idea of two codons/binding sites;
- (Allows) tRNA with anticodons to bind/associate;
- (Catalyses) formation of peptide bond between
amino acids (held by tRNA molecules); - Moves along (mRNA to the next
codon)/translocation described;
