Protein Synthesis D1.2 Flashcards
What is transcription?
the synthesis of RNA using DNA as a template. the GENE sequence of the DNA is copied in the mRNA.
Where does transcription take place?
the nucleus
What does a gene on the DNA sequence do?
specify the sequence of amino acids.
- DO NOT give any observable characteristics in an organism.
What actually give the observable characteristics in an organism?
proteins often directly or indirectly determine observable characteristics.
What is the RNA Polymerase?
an enzyme that is used in transcription and is responsible for:
- binding to the start of a gene in DNA
- separating the gene section of the DNA double helix
- pairing up and adding the RNA nucleotides complementary bases (uracil replaces thymine)
What is the first step of transcription?
the enzyme RNA polymerase binds to a site on the DNA at the START of a gene sequence.
What happens after the RNA Polymerase has bound to the DNA?
RNA polymerase moves along the gene sequence of the DNA and separates the double stranded DNA.
What happens after the RNA Polymerase has separated the DNA?
RNA polymerase pairs and adds RNA nucleotides with complementary bases along the template DNA going from 3’ to 5’.
- hydrogen bonds created between DNA and mRNA
- covalent bonds created between RNA molecules
What happens after the RNA Polymerase has paired the RNA nucleotides?
the mRNA is separated from the DNA at the END of the gene sequence and the DNA double helix reforms.
What is the antisense strand?
it is the template strand, the strand that the mRNA is bound to for creation of the mRNA strand. it is from 3’ to 5’.
What is the sense strand?
it is the non-template strand that does not partake in the copying process. it is the strand that the mRNA is actually trying to copy. it is from 5’ to 3’.
- identical to the mRNA strand (switch U with T)
What does it mean for DNA to be stable?
it does not change its code easily.
How is DNA stable?
stability is ensured by the sugar-phosphate backbone and hydrogen bonds between nucleotides.
What is the stability of DNA important for?
the conservation of the original code.
What do some somatic cells that do not divide to replace itself need to do?
must stay unchanged throughout life because they will be broken forever.
How can the stability of DNA be damaged?
free radicals,
chemicals,
cigarette smoke,
exposure to UV,
nuclear radiation.
What can instability of DNA lead to?
mutations (harmful or beneficial)
Why do DNA instability occur as a result of the ways of damage?
there are repair mechanisms to fix but not always successful.
What is gene expression?
the process by which the info carried by a gene is turned into an observable characteristic on an organism.
How does gene expression occur?
by transcription and translation.
What is the process of gene expression as it happens in the cell?
DNA –> mRNA –> polypeptide –> observable change
How come some genes are not expressed even when it is transcribed?
genes can be turned on and off and the expression of a cell depend on info from both inside and outside the cell. transcription, being the first stage of gene expression, is a key
stage at which expression of a gene can be switched on and off
What is genetic code?
the set of rules by which info encoded in mRNA sequences is converted to proteins by living cells.
What does genetic code do?
carries the message for the sequences of amino acids in a polypeptide.
What is a codon?
three bases transcribed strand correspond to one triplet of bases.
What does a codon do?
codes for an amino acid and therefore genetic code.
What is universality?
all organisms use the same 4 letter code in genetic code. (ATGC)
What is degeneracy?
- of genetic code is the fact that different combinations of codons can result in expressing the same amino acid.
What is the role of tRNA in translation?
these molecules translate the base sequence of mRNA to an amino acid sequence.
What does tRNAs have?
- have an anticodon of three bases that bind to a codon on mRNA via complementary base pairing.
- amino acids corresponding to their codon that pairs with the mRNA codon that codes for the AA.
What is the role of mRNA in translation?
has a site to which a ribosome can bind and a sequence of codons that specify the amino acids sequence.
- can be translated many times
What is the role of ribosomes in translation?
act as the binding site for mRNA and tRNA. catalyzing peptide bonds between amino acids
Where does translation take place?
free AND OR membrane bound ribosomes
What are ribosomes of translation composed of?
two subunits: small and large
- composed of long rRNA strands
What does the subunits of ribosomes do in translation?
they lock together and trap mRNA between the space.
What is translation? (define)
stepwise movement of the ribosome along mRNA and linkage of amino acids by peptide bonding to the growing polypeptide chain.
What is the first step of translation?
small ribosomal subunit attach to the mRNA and slides along the molecule in a 5’ to 3’ direction until it sees a start codon. (AUG)
What happens after the ribosome sees the start codon?
tRNA loaded with an amino acid specific to the corresponding anticodon, attaching to a site on the ribosome: P-site
What happens after the tRNA has attached to the P-site after the AUG?
large ribosomal subunit can bind to close the complex.
What happens once the ribosome has closed?
the second tRNA carrying an amino acids binds w/its anticodon to the complementary codon at the A-site of the ribosome.
What happens after the tRNA has bound to the A-site?
polypeptide bond formation between amino acids on the tRNA and the amino acid in the P-site. the polypeptide formed by this is transferred to the tRNA on the A-site.
What happens after the amino acid chain has been transferred to the tRNA on the A-site?
the ribosome moves along the mRNA by one codon in 5’ to 3’ direction, causing the second tRNA to move from A to P-site and te first from P to E-site.
Required molecules for transcription
DNA, RNA polymerase, NTPs
Required molecules for translation
mRNA, ribosomes, tRNA
Coding sequence for transcription
DNA
Coding sequence for translation
mRNA
Product of transcription
mRNA
Product of translation
polypeptide
Location of transcription
nucleus
Location of translation
free or membrane bound ribosomes
Direction of synthesis of transcription
5’ > 3’
Direction of synthesis of translation
5’ > 3’
Source of energy for transcription
ATP fro cellular respiration
Source of energy for translation
ATP
What is a gene mutation?
a change to the base sequence of a gene.
What is sickle cell anemia?
a disease which is caused by a mutation in the DNA that changes the oxygen transporting polypeptide structure of the protein hemoglobin (found in red blood cells)
Which human chromosome does the mutation happen for sickle cell anemia? What type of mutation is it?
11, single base substitution mutation
What does the mutation cause the polypeptide of that gene do?
change shape and structure?
The normal beta globin of blood VS the mutated beta of blood
CTC vs. CAC
GAG vs. GUG
glu vs. val
Consequences of sickle cell anemia
- rigid fibers
- change in shape to crescent like
- reduced capacity to carry oxygen
- destroyed quicker
- pain in bones and joints
- organ damage
- clots easily
What causes the sickle cell to become rigid?
hydrophobic interactions between amino acids in the protein
