Topic 4 Genetic Info Variation And Relationships Between Organsisms - DNA Genes And Chromosomees Flashcards
Differences of dna in prokaryotic and eukaryotic cells
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
Compare and contrast DNA in eukaryotic cells with DNA in prokaryotic cells- similarities
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
What is a chromosome?
● Long, linear DNA + its associated histone proteins
● In the nucleus of eukaryotic cells
What is a gene?
A sequence of DNA (nucleotide) bases that codes for:
● The amino acid sequence of a polypeptide
● Or a functional RNA (eg. ribosomal RNA or tRNA)
Define locus
What is a locus?
Fixed position a gene occupies on a particular DNA molecule.
Describe the nature of the genetic code
Triplet code A sequence of 3 DNA bases, called a triplet, codes for a specific amino acid
Universal The same base triplets code for the same amino acids in all organisms
Non-overlapping Each base is part of only one triplet so each triplet is read as a discrete unit
Degenerate An amino acid can be coded for by more than one base triplet
What are ‘non-coding base sequences’ and where are they found?
Non-coding base sequence- DNA that does not code for amino acid sequences / polypeptides:
1. Between genes - eg. non-coding multiple repeats
2. Within genes- introns
What does much of the nuclear dna in eukaryotes not do?
In eukaryotes, much of the nuclear DNA does not code for polypeptides.
What is an exon?
Base sequence of a gene coding for amino acid sequences (in a polypeptide)
What is an intron ?
Base sequence of a gene that doesn’t code for amino acids, in eukaryotic cells
Define genome
The complete set of genes in a cell (including those in mitochondria and /or chloroplasts)
Define proteome
The full range of proteins that a cell can produce (coded for by the cell’s DNA / genome)
What are the two stages of protein synthesis?
Transcription Production of messenger RNA (mRNA) from DNA, in the nucleus
Translation Production of polypeptides from the sequence of codons carried by mRNA, at ribosomes
Similarities of tRNA and mRNA
Both single polynucleotide strand
Differences of tRNA and mRNA
● tRNA is folded into a ‘clover leaf shape’
, whereas
mRNA is linear / straight
● tRNA has hydrogen bonds between paired bases,
mRNA doesn’t
● tRNA is a shorter, fixed length, whereas mRNA is a
longer, variable length (more nucleotides)
● tRNA has an anticodon, mRNA has codons
● tRNA has an amino acid binding site, mRNA doesn’t
Describe the steps of transcription
Hydrogen bonds between DNA bases break
Only one DNA strand acts as a template
Free RNA nucleotides align next to their complementary bases on the template strand
● In RNA, uracil is used in place of thymine (pairing with adenine in DNA)
RNA polymerase joins adjacent RNA nucleotides
This forms phosphodiester bonds via condensation reactions
Pre-mRNA is formed and this is spliced to remove 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-mRNA produced in eukaryotic cells whereas mRNA is produced directly in prokaryotic cells
● Because genes in prokaryotic cells don’t contain introns so no splicing in prokaryotic cells
Describe the steps of translation
mRNA attaches to a ribosome and the ribosomemoves to a start codon (AUG)
tRNA brings a specific amino acid
tRNA anticodon binds to complementary mRNA
codon
Ribosome moves along to next codon and another
tRNA binds so 2 amino acids can be joined by a
condensation reaction forming a peptide bond
● Using energy from hydrolysis of ATP
tRNA released after amino acid joined polypeptide
Ribosome moves along mRNA to form the
polypeptide, until a stop codon is reached
What is the role of ATP in translation?
Hydrolysis of ATP to ADP + Pi releases energy So amino acids join to tRNAs and peptide bonds form between amino acids
What is the role of tRNA in translation?
Attaches to / transports a specific amino acid, in relation to its anticodon
tRNA anticodon complementary base pairs to mRNA codon, forming hydrogen bonds
2 tRNAs bring amino acids together so peptide bond can form
What is the role of ribosomes in translation?
mRNA binds to ribosome, with space for 2 codons
Allows tRNA with anticodons to bind
Catalyses formation of peptide bond between amino acids (held by tRNA molecules)
Moves along (mRNA to the next codon) / translocation
Describe how the base sequence of nucleic acids can be related to the
amino acid sequence of polypeptides when provided with suitable data
● You may be provided with a genetic code to identify which
triplets / codons produce which amino acids (example shown)
● tRNA anticodons are complementary to mRNA codons
○ Eg. mRNA codon = ACG → tRNA anticodon = UGC
● Sequence of codons on mRNA are complementary to sequence
of triplets on DNA template strand
○ Eg. mRNA base sequence = ACG UAG AAC
→ DNA base sequence = TGC ATC TTG
● In RNA, uracil replaces thymine
