B8- DNA, Genes and Protein Synthesis Flashcards
What are the similarities between DNA in eukaryotic genes and prokaryotic
Nucleotide structure is identical - deoxyribose attached to phosphate and a base
Adjacent nucleotides joined by phosphodiester bonds, complementary bases joined by hydrogen bonds
DNA in mitochondria / chloroplasts have similar structure to DNA in prokaryotes
○ Short, circular, not associated with proteins
Differences between prokaryotic and eukaryotic DNA
Eukaryotic DNA is longer
Eukaryotic DNA is linear, prokaryotic DNA is circular
Eukaryotic DNA is associated with histone proteins, prokaryotic DNA is not
Eukaryotic DNA contain introns, prokaryotic DNA does not
What is a chromosome?
- Long, linearDNA + its associatedhistone proteins
- In thenucleusofeukaryoticcells
What is a gene?
A sequence ofDNA (nucleotide) basesthat codes for:
- Theamino acid sequenceof apolypeptide
- Or afunctional RNA(eg. ribosomal RNA or tRNA)
What is a locus?
Fixed positionageneoccupies on a particularDNAmolecule.
Triplet code
A sequence of3 DNA bases, called a triplet, codes for aspecific amino acid
Universal
Thesame base tripletscode for thesame amino acidsinallorganisms
Non-overlapping
Each base is part of onlyone tripletso each triplet is read as adiscreteunit
Degenerate
An amino acid can be coded for bymore than one base triplet
What are ‘non-coding base sequences’ and where are they found?
Non-coding base sequence- DNA that doesnot code for amino acid sequences / polypeptides:
- Between genes -eg. non-coding multiple repeats
- Within genesintrons
Exon
Base sequence of a genecoding for amino acid sequences(in a polypeptide)
Intron
Base sequence of a gene thatdoesn’t code for amino acids, in eukaryotic cells
Genome
The complete set ofgenesin a cell (including those in mitochondria and /or chloroplasts)
Compare and contrast the structure of tRNA and mRNA
Comparison (similarities)
- Bothsinglepolynucleotide strand
Contrast (differences)
- tRNA is folded into a‘clover leaf shape’, whereas mRNA islinear/ straight
- tRNA hashydrogen bondsbetween paired bases, mRNA doesn’t
- tRNA is ashorter, fixedlength, whereas mRNA is alonger, variablelength (more nucleotides)
- tRNA has ananticodon, mRNA hascodons
- tRNA has anamino acid binding site, mRNA doesn’t
Describe how mRNA is formed by transcription in eukaryotic cells
- Hydrogen bondsbetween DNA bases break
- OnlyoneDNA strand acts as atemplate
- FreeRNA nucleotidesalign next to theircomplementary baseson the template strand (In RNA,uracilis used in place of thymine (pairing with adenine in DNA)
- RNA polymerasejoinsadjacentRNA nucleotides
- This formsphosphodiester bondsviacondensationreactions
- Pre-mRNAis formed and this issplicedtoremove introns, forming (mature) mRNA
Describe how production of messenger RNA (mRNA) in a eukaryotic cell is different from the production of mRNA in a prokaryotic cell
- Pre-mRNAproduced ineukaryoticcells whereasmRNAis produced directly inprokaryoticcells
- Becausegenesin prokaryotic cellsdon’t contain intronssono splicingin prokaryotic cells
Describe how translation leads to the production of a polypeptide?
- mRNA attaches to aribosomeand the ribosome moves to astart codon(AUG)
- tRNA brings aspecific amino acid
- tRNA anticodonbinds tocomplementary mRNA codon
- Ribosome moves along tonext codonand another tRNA binds so2 amino acidscan be joined by acondensation reactionforming apeptide bond (Using energy fromhydrolysis of ATP)
- tRNAreleasedafter amino acid joined polypeptide
- Ribosome moves alongmRNA to form the polypeptide, until astop codonis reached
Role of ATP in translation
- Hydrolysis of ATP to ADP + Pireleases energy
- So amino acidsjoin totRNAsandpeptide bondsform between amino acids
Role of tRNA in translation
- Attaches to / transports aspecific amino acid, in relation to its anticodon
- tRNAanticodon complementary base pairs to mRNA codon, forming hydrogen bonds
- 2 tRNAs bringamino acidstogether sopeptide bond canform
Role of ribosomes in translation
- mRNAbinds to ribosome, with space for 2 codons
- Allows tRNA withanticodonsto bind
- Catalyses formation ofpeptide bondbetween amino acids (held by tRNA molecules)
- Moves along(mRNA to the next codon) / translocation
