B8 - DNA, Genes & Protein Synthesis Flashcards
What is the DNA in prokaryotes?
Have a nucleoid- a single, circular chromosomal DNA molecule, which is double stranded
They also have plasmids: small, circular DNA molecules
The DNA within prokaryotic cells is not associated with any proteins
What is the DNA in eukaryotes?
In the nucleus of eukaryotic cells, DNA molecules are very long, linear and associated with proteins, called histones.
Tightly coiled DNA + histone proteins = Chromatin → coils & condenses even more → forms a Chromatid
What is the function of histone proteins?
Organise & condense the DNA tightly → fits into the nucleus
What joins together 2 chromatins to from a chromosome?
Centromere
What is the DNA in chloroplasts and mitochondria like?
It is like the DNA of prokaryotes, is short, circular and not associated with protein
What is a gene?
It is a base sequence of DNA that codes for:
The amino acid sequence of a polypeptide
A functional RNA (including ribosomal RNA and tRNAs)
What are the functional RNA molecules?
Messenger RNA (mRNA): the base sequences on these molecules are used by ribosomes to form polypeptide chains
Transfer RNA (tRNA): amino acids are carried to the ribosome by these molecules
Ribosomal RNA (rRNA): these molecules form part of the structure of ribosomes
What is loci/locus?
The position of a gene on a chromosome
Alleles may have slightly different nucleotide sequences, but still occupy the same position on the chromosome
What is a triplet of bases called?
A codon
What is the use of start and stop signal triplet codes?
This ensures that the cell reads DNA correctly, so the code is non-overlapping and produces the correct sequence of amino acids
How is the effect of mutations limited?
Multiple codons can code for the same amino acids
How is the genetic code universal?
As almost every organism on earth uses the same code, and the same set of amino acids
What are non-coding sections of DNA within genes called?
Introns
What are Non-coding DNA sections between genes called?
Introns
What is the name for regions of the DNA that code for proteins?
Exons
What happens to pre-mRNA before it leaves the nucleus?
The introns are removed, and exons are joined together in a process called splicing
Are introns present in prokaryotic cells?
No
What is a genome?
A genome is the complete set of genes present in a cell
The full genome of an organism is present within every one of it’s cells, but not every gene is expressed in every cell
What is a proteome?
The proteome is the full range of proteins that a cell is able to produce
Usually larger than the genome of an organism
What is the structure of mRNA?
Made up of one polynucleotide strand
Much shorter compared to DNA
It is made up of a sugar-phosphate backbone and exposed unpaired bases
Uracil bases are present instead of thymine bases
What is the structure of tRNA?
A single-stranded molecule
Has a sugar-phosphate backbone
It has a folded shape
Hydrogen bonds between some of the complementary bases
Amino acids bind to specific regions of the molecule
The specific anticodon found on the tRNA molecule is complementary to a specific codon on an mRNA molecule
What are the 2 stages of protein synethesis?
Transcription
Translation
What occurs in the transcription stage of protein synthesis?
Helicase breaks hydrogen bonds between complementary base pairs, causes the DNA molecule to unwind, gene to be transcribed is now exposed
Free, activated RNA nucleotides pair up (via hydrogen bonding) with their complementary, exposed bases on the unzipped template strand
Sugar-phosphate backbone of mRNA molecule forms by RNA polymerase
Hydrogen bonds between template strand and newly-synthesised mRNA break → the original double helix re-forms
mRNA leaves the nucleus via the nuclear envelope, original DNA stays
What’s the difference between the transcription of prokaryotic and eukaryotic cells?
Prokaryotic transcription of DNA results in the production of mRNA
Eukaryotic transcription of DNA results in the production of pre-mRNA
