DNA, genes and protein synthesis Flashcards
What is a gene?
A section of DNA that contains the coded information for making polypeptides and functional RNA, located at the locus
How do genes control the characteristics of an organism?
Genes code for proteins (enzymes) and these control chemical reactions and therefore the development and activities of an organism
What is the minimum number of bases that must code for one amino acid?
3
How many different amino acids regularly occur in proteins?
20
What is a triplet?
Three bases code for each amino acid
What is a degenerate code?
Multiple different codons will give the same amino acid
How many triplets code for amino acids that need more than one?
2-6
What happens to the starting codon on the polypeptide?
If not needed in the final molecule, it is removed at the end
What are the ‘stop codes’?
Three triplets don’t code for any amino acids and they mark the end of the polypeptide chain
What is non-overlapping?
Each base in the sequence is only read once
Why is the code universal?
Few minor exceptions, but each triplet codes for the same amino acid in all organisms
What are exons?
Coding sequences of DNA
What are introns?
Non-coding regions of DNA
What else do genes code for?
rRNA and tRNA
What is the DNA in a prokaryote like?
Shorter, form a circle and aren’t associated with proteins, therefore they don’t have chromosomes
What is the DNA in a eukaryote like?
Longer, form a line and are associated with histones to form chromosomes
When are chromosomes visible?
Distinct structure when cells are dividing
How are chromosomes seen at the start of cell division?
Two threads, joined at a single point
What is each thread of the chromosome during cell division called?
Chromatid as DNA has already replicated
What is a locus?
A specific position of a gene on a DNA molecule
What are homologous pairs?
Where one of each chromosome is derived from the mother and father
What is the diploid number?
The total number of chromosomes in an adult cell, not the number of pairs
What is the diploid number in humans?
46
What is the difference between the chromosomes in a homologous pairs?
Carry the same gene but not always the same allele
What is an allele?
One of the number of alternative forms of a gene
What happens when the alleles are different?
Each allele has a different base sequence, therefore a different amino acid sequence, so produces a different polypeptide
What is a mutation?
Changes in the base sequence of gene, which creates a new allele of that gene
How do mutations affect the protein produced?
May not function properly or at all, enzymes may have a different shape and not be able to form ES complexes
How is DNA transferred into the cytoplasm to make proteins?
Transcribed onto mRNA
What is a codon?
Sequence of three bases on mRNA that codes for a single amino acid (complimentary to DNA)
What is the genome?
The complete set of genes in a cell, including those in the mitochondria/chloroplasts
What is the proteome?
Proteins produced by a given type of cell under a certain set of conditions
What is the complete proteome?
The full range of proteins produced by the genome
What are the nucleotides of RNA made up of?
Pentose sugar ribose, AUCG bases and a phosphate group
What determines the base sequence of mRNA?
Transcription of DNA
What does mRNA do once it leaves the nuclear pores?
Associates with the ribosomes, where it acts as a template for protein synthesis
How many mono-nucleotides make up mRNA?
Thousands
How many mono-nucleotides make up tRNA?
Around 80
What is the structure of tRNA?
Single-stranded chain folded into a clover-leaf shape, with one end of the chain extending beyond the other
Why are there many different tRNA molecules?
Each attach to a different amino acid
What is an anticodon?
Three bases at the opposite end of a tRNA molecule, on the anticodon loop
What happens during protein synthesis with tRNA?
An anticodon pairs with the three complimentary organic bases that make up the codon on mRNA, tRNA attaches to amino acids and lines them up on the mRNA template
In what form does DNA provide instructions?
Long sequences of bases
What is transcription?
The formation of pre-mRNA from part of DNA sequences
How does pre-mRNA become mRNA?
Splicing
What is translation?
mRNA is used as a template to which complimentary tRNA molecules attach and the amino acids they carry are linked to form a polypeptide
What enzyme forms pre-mRNA?
RNA polymerase
How many base pairs are exposed on a DNA molecule at once?
About 12
When is splicing necessary?
In eukaryotic cells, as there are introns
Why must introns be removed?
They would prevent the synthesis if polypeptides
How many different tRNA molecules are there?
60
What does the ribosomes attach to on the mRNA molecule?
The starting codon
What happens when the ribosome and mRNA attach?
The tRNA molecule with the complimentary anticodon sequences moves and pairs up with the codon on mRNA
How many tRNA molecules act at once on mRNA?
2
How are two amino acids joined together?
By a peptide bond, using an enzyme and ATP which is hydrolysed
How many amino acids are added to a polypeptide chain each second?
Up to 15
What happens when the ribosome reaches stop codon?
Ribosome, tRNA and mRNA separate and the polypeptide chain is complete
Why do up to 50 ribosomes pass immediately behind the first?
So many identical polypeptides can be assembled simultaneously
