Genetics and Diversity - Protein Synthesis Flashcards
What is the minimum number of base pairs that code for each amino acid and why?
3 base pairs:
as there are only 4 bases, two pairs would not produce the range of amino acids that we use
What is degenerate code?
When more that one triplet is needed for an amino acid
What is a codon/triplet?
3 base pairs that codes for a specific amino acid or signals the start or end of a sequence
Which direction do the left and right strands of DNA run in?
Left: 5’ to 3’
Right: 3’ to 5’
What are the functions of the antiparallel strands in DNA?
- maintains 2 copies of the DNA in case of mutation
- protects the bases
- required for semi-conservative replication
- improves molecular stability
What is a gene?
A section of DNA on a homologous chromosome at a specific position (the locus)
What information does a gene carry?
The information to produce the amino acid sequence of a polypeptide
What are the features of prokaryotic DNA?
- free in the cytoplasm - no nucleus
- naked
- singular circular chromosome
- may contain plasmids
What is a plasmid?
a smaller, separate loop of DNA
What are the features of eukaryotic DNA?
- Located in a double membrane-bound nucleus
- Wound around histone proteins
- Multiple linear chromosomes
- No plasmids
What are introns?
Sections of DNA that don’t code for polypeptides (non-coding DNA)
What are exons?
Coding sequences of DNA
How many chromosomes do humans have?
46 chromosomes or 23 homologous pairs
What are the differences betwen RNA and DNA?
- Uracil used instead of Thymine in RNA
- RNA only has 1 strand
- RNA - ribose sugar, DNA - deoxyribose sugar
- RNA is shorter than DNA
What are the 3 types of RNA?
mRNA
tRNA
rRNA
What is the general function of RNA?
to transfer coded information from DNA into the cytoplasm where it can be translated into proteins
What does mRNA stand for?
messenger RNA / messenger ribonucleic acid
What is the function of mRNA?
to transcribe the code for the gene in the DNA and carry it from the nucleus to the cytoplasm
What are the features of mRNA?
can travel through nuclear pores
single stranded helix
has a short lifetime
What does tRNA stand for?
transfer RNA / transfer ribonucleic acid
What is the function of tRNA?
to match the triplet code in mRNA to their respective amino acids
What are the features of tRNA?
only 80 nucleotides long
folds up by complementary base pairing to form a 3D looped clover structure
middle loop contains the anticodon
What is an anticodon?
the tRNA codon complimentary to an mRNA codon that attaches the appropriate amino acid
What does rRNA stand for?
ribosomal RNA / ribosomal ribonucleic acid
What is the function of rRNA?
to work with proteins to synthesise ribosomes
What is transcription?
The process of making pre-mRNA using part of the DNA as a template/coding strand
What are the stages of transcription?
- RNA polymerase binds to section of DNA
- Hydrogen bonds are broken, exposing the bases
- Nucleotides on template strand bind to complementary RNA molecules
- RNA polymerase moves along the strand, joining the RNA nucleotides together and releasing them
- DNA strands rejoin once RNA polymerase has passed
- RNA polymerase reaches stop codon and detaches
Why does pre-mRNA need to be spliced?
Because the sequence includes both introns and exons, so the introns need to be removed
Why does prokaryotic mRNA not need to be spliced?
Prokaryotic DNA contains no introns
How can the same sequence of DNA code for several proteins?
the exon sections can be joined together in different ways during splicing, producing different sequences
What is splicing?
the process of removing introns from pre-mRNA and joining the exons together to form mature mRNA
What is translation?
the process of converting the codon sequence in the mRNA molecule into an amino acid sequence
What are the stages of translation?
- mRNA leaves nucleus after splicing
- a ribosome attaches to the start codon
- the complementary tRNA molecule binds to the first codon
- a second tRNA molecule binds to the second codon
- a peptide bond forms between the 2 amino acids
- the ribosome moves along the mRNA to the next codon and the first tRNA is released
- the process repeats until the stop codon is reached
What catalyses the peptide bond during translation?
enzymes and ATP
How many amino acids can be added per second during translation?
15
What is post-translational modification?
the process of modifying proteins so that they can become fully functional - secondary, tertiary and quaternary protein structures
What carries out post-translational modification?
enzymes
