IB biology: topic 2: protein synthesis

what is the code that is used to assemble proteins?

DNA

what does one gene code for?

one protein (polypeptide chain)

what does the order of base in the gene determine?

the order in which amino acids are joined together.

why is transcription needed?

DNA is too large to leave the nucleus, so a copy is made in a smaller chemical, known as mRNA

what is translation? (overview)

mRNA moves to ribosomes outside the nucleus where the RNA code is used to assemble the amino acids into a chain.

where are VNTRs found?

non-coding sections of genes

where in the sequence does transcription start?

at the 5’ prime end of the new mRNA sequence.

where in the sequence does transcription end?

poly A tail

what is the function of tRNA?

reads the mRNA codons and brings the corresponding amino acids into the ribosomes

what do tRNA molecules have to ensure the correct amino acid is used?

an anticodon which is complementary to a specific codon on mRNA - the amino acid that corresponds to the anticodon binds to the specific attachment sight on the tRNA

what is the function of mRNA?

transcribed from the DNA in the nucleus to produce a single-stranded RNA

what is a poly A tail?

15 nucleotides with repeated As.

when does transcription start?

after RNA polymerase binding to a promoter region (if the RNA Polymerase cannot bind to a promoter transcription will not start).

what does the RNA polymerase do in transcription?

binds to the target gene to begin transcription,

pairs up the complementary bases with free nucleotides

what is different about bases of nucleotides in transcription?

uracil replaces thymine

what type of bonds form between the adjacent free nucleotides

covalent bonds

when does transcription stop?

when the RNA Polymerase reaches the stop codon

where is the promoter region found on the DNA in relation to the genes it regulates?

upstream of the genes they regulate

what is transcription? (detailed process)

RNA polymerase binds to a promoter region, breaking hydrogen bonds between two strands.

RNA polymerase pairs up free RNA nucleotides with complementary bases. Covalent bonds form between the free nucleotides.

When the RNA polymerase reaches the stop codon, transcription stops. The RNA separates, forming mRNA strand and the helix/hydrogen bonds reform in DNA strands.

what are exons?

the sections of DNA that code for proteins

in what direction does transcription occur in?

5’ to 3’ direction

in what direction does transcription occur? on what strand?

in the 5’ to 3’ direction on the anti-sense strand (that way the mRNA strand is identical to the one we need to code for the protein)

what is translation? (detailed process)

mRNA binds to a ribosome,

a tRNA molecule that has an anticodon binds to the first codon (complementary),

the tRNA molecule carries a specific amino acid that is bound to it using ATP, another tRNA binds to mRNA with corresponding amino acid,

a peptide bond forms between the amino acids and the ribosome moves along the mRNA strand and the process repeats,

when the ribosome reaches the STOP codon there is no corresponding tRNA molecule and the polypeptide chain is released

what is initiation? (translation)

start codon of mRNA molecule binds to rRNA of ribosome,

tRNA binds to the first codon,

the tRNA has an anticodon that is complementary to a specific codon

what are the sites in translation?

A, P, E

what is elongation? (translation)

the first amino acid joins at the P site,

eongation proceeds them entering the A site and then shifting to the P site followed by the E site. This repeats until termination.

what is degenerate code?

code where some amino acids are specified by more than one codon.

how many bases/codons can fit inside the ribosome at one time?

6 bases / 2 codon

what is the genome?

the complete set of genes in an individual’s DNA

what is the proteome?

the range of proteins an individual can produce

what is a codon?

a specific sequence of three bases

what does a codon do?

codes for a specific amino acid

how does transcription differ in prokaryotes and eukaryotes?

mRNA in eukaryotes is known as pre-mRNA and is sliced before entering the ribosome for translation.

in prokaryotes the mRNA produced in the complete form and no splicing takes place

how does RNA polymerase differ in prokaryotes and eukaryotes?

in prokaryotes, RNA polymerase catalyses every step of transcription.

in eukaryotes, it only produced the mRNA strand (DNA helicase separates DNA strands)

what are introns?

sequences of nucleotides that are removed to form mature RNA in eukaryotes

what is splicing?

a process that removes sections of non-coding DNA (introns) from the mRNA molecule

what is a polysome?

mRNA with 2 or more ribosome attached

does the small or large subunit move along the mRNA strand?

small subunit moves along mRNA strand