1.4 Genetics, Biodiversity and Classification Flashcards
4.1 DNA, genes and chromosomes
Compare and contrast DNA in eukaryotic cells with DNA in prokaryotic cells (3) (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)
4.1 DNA, genes and chromosomes
Compare and contrast DNA in eukaryotic cells with DNA in prokaryotic cells (3) (Differences)
- 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
4.1 DNA, genes and chromosomes
What is a chromosome ?
- Long, linear DNA + its associated histone proteins
- In the nucleus of eukaryotic cells
4.1 DNA, genes and chromosomes
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)
4.1 DNA, genes and chromosomes
What is a locus ?
Fixed position a gene occupies on a particular DNA molecule
4.1 DNA, genes and chromosomes
Describe the nature of the genetic code
- Triplet code
- Universal
- Non-overlapping
- Degenerate
4.1 DNA, genes and chromosomes
Describe what is meant by Triplet Code :
A sequence of 3 DNA bases, called a triplet, codes for a specific amino acid
4.1 DNA, genes and chromosomes
Describe what is meant by Universal :
The same base triplets code for the same amino acids in all organisms
4.1 DNA, genes and chromosomes
Describe what is meant by Non-Overlapping :
Each base is part of only one triplet so each triplet is read as a discrete unit
4.1 DNA, genes and chromosomes
Describe what is meant by Degenerate :
An amino acid can be coded for by more than one base triplet
4.1 DNA, genes and chromosomes
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:
- Between genes - eg. non-coding multiple repeats
- Within genes - introns
In eukaryotes, much of the nuclear DNA does not code for polypeptides
4.1 DNA, genes and chromosomes
What are introns and exons ?
- Intron : Base sequence of a gene that doesn’t code for amino acids, in eukaryotic cells
- Exon : Base sequence of a gene coding for amino acid sequences (in a polypeptide)
4.2 DNA and protein synthesis
Define a Genome
The complete set of genes in a cell (including those in mitochondria and /or chloroplasts)
4.2 DNA and protein synthesis
Define a Proteome
The full range of proteins that a cell can produce (coded for by the cell’s DNA / genome)
4.2 DNA and protein synthesis
Describe 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
4.2 DNA and protein synthesis
Compare and contrast the structure of tRNA and mRNA
4.2 DNA and protein synthesis
Describe how mRNA is formed by transcription in eukaryotic cells
- 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
4.2 DNA and protein synthesis
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
4.2 DNA and protein synthesis
Describe how translation leads to the production of a polypeptide
- mRNA attaches to a ribosome and the ribosome moves 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
4.2 DNA and protein synthesis
Describe 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
4.2 DNA and protein synthesis
Describe 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
4.2 DNA and protein synthesis
Describe 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 two differences between the structure of a tRNA molecule and the structure of an mRNA molecule (2)
- tRNA is ‘clover leaf shape’, mRNA is linear
- tRNA has hydrogen bonds, mRNA does not
- tRNA has an amino acid binding site, mRNA does not
- tRNA has anticodon, mRNA has codon
In a eukaryotic cell, the structure of the mRNA used in translation is different from the structure of the pre-mRNA produced by transcription. Describe and explain a difference in the structure of these mRNA molecules (2)
- mRNA has no introns/has (only) exons / mRNA fewer nucleotides
- (Because of) splicing
Describe how one amino acid is added to a polypeptide that is being formed at a ribosome during translation (3)
- tRNA brings specific amino acid (to ribosome)
- Anticodon (on tRNA) binds to codon (on mRNA)
- Amino acids join by condensation reaction (using ATP)
Describe how mRNA is produced from an exposed template strand of DNA.
Do not include DNA helicase or splicing in your answer (3)
- (Free RNA) nucleotides form complementary base pairs (H-Bonds)
- Phosphodiester bonds form
- By (action of) RNA polymerase
Define the term exon (1)
Base/nucleotide/triplet sequence coding for polypeptide/sequence of amino acids/primary structure
Describe how mRNA is formed by transcription in eukaryotes (5)
- Hydrogen bonds (between DNA bases) break
- (Only) one DNA strand acts as a template
- (Free) RNA nucleotides align by complementary base pairing
- (In RNA) Uracil base pairs with adenine (on DNA)
- RNA polymerase joins (adjacent RNA) nucleotides
- (By) phosphodiester bonds (between adjacent nucleotides)
- Pre-mRNA is spliced (to form mRNA)
- To remove Introns
Describe how a polypeptide is formed by translation of mRNA (6)
- (mRNA attaches) to ribosomes
- (tRNA) anticodons (bind to) complementary (mRNA) codons
- tRNA brings a specific amino acid
- Amino acids join by peptide bonds
- (Amino acids join together) with the use of ATP - condensation reaction
- tRNA released (after amino acid joined to polypeptide)
- The ribosome moves along the mRNA to form the polypeptide
- Change in the base/nucleotide (sequence of chromosomes/DNA)
- Results in the formation of new allele
- Has no effect if :
- Genetic code is degenerate (so amino acid sequence may not change)
- Mutation is in an intron (so amino acid sequence may not change)
- Does change amino acid but no effect on tertiary structure
- (New allele) is recessive so does not influence phenotype;
- Has an effect if :
- Results in change in polypeptide that positively changes the properties (of the protein)
- May result in increased reproductive success
- May result in increased survival (chances)
What is the proteome of a cell? (1)
- (The proteome is the full) range of / number of different proteins that a cell is able to produce (at a given time)
- a ) Translation
- b ) tRNA
- c ) TAC, UAC
Suggest how the production of a protein with one amino acid missing may lead to a genetic disorder such as Ellis-van Creveld syndrome (2)
- Different genes
- Different (DNA) base sequences
A mutation of a tumour suppressor gene can result in the formation of a tumour. Explain how (2)
- (Tumour suppressor) gene inactivated / not able to control
- Rate of cell division too fast / out of control
Not all mutations result in a change to the amino acid sequence of the
encoded polypeptide. Explain why
- (Genetic) code degenerate
- Mutation in intron
Describe how a gene is a code for the production of a polypeptide. Do not
include information about transcription or translation in your answer (3)
- (Because) base/nucleotide sequence
- (In) triplet(s)
- (Determines) order/sequence of amino acid sequence/primary
structure (in polypeptide)
- (Associated with) histones/proteins v no histones/proteins
- Linear v circular;
- No plasmids v plasmids
- Introns v no introns
- Long(er) v short(er)
Define ‘non-coding base sequences’ and describe where the non-coding
multiple repeats are positioned in the genome (2)
- DNA that does not code for protein/polypeptides
- (Positioned) between genes
The nucleus and a chloroplast of a plant cell both contain DNA.
Give three ways in which the DNA in a chloroplast is different from DNA in the nucleus (3)
- In chloroplasts :
- DNA shorter
- Fewer genes
- DNA circular not linear
- Not associated with protein/histones, unlike nuclear DNA
- Introns absent but present in nuclear DNA
Some DNA nucleotides have the organic base thymine, but RNA
nucleotides do not have thymine. RNA nucleotides have uracil instead of
thymine.
Give one other difference between the structure of a DNA nucleotide and
the structure of an RNA nucleotide (1)
Deoxyribose in DNA and ribose in RNA
W = amino acid binding site and X = anticodon
Not all mutations in the nucleotide sequence of a gene cause a change in
the structure of a polypeptide. Give two reasons why (2)
- Triplets code for same amino acid (Triplets are degenerate)
- Occurs in introns /non-coding sequence
Compare and contrast the DNA in eukaryotic cells with the DNA in
prokaryotic cells (5)
- Comparison
- Nucleotide structure is identical
- Nucleotides joined by phosphodiester bond
- DNA in mitochondria / chloroplasts same / similar (structure) to DNA in prokaryotes
- Contrasts
- Eukaryotic DNA is longer
- Eukaryotic DNA contain introns, prokaryotic DNA does not
- Eukaryotic DNA is linear, prokaryotic DNA is circular
- Eukaryotic DNA is associated with / bound to protein / histones,
prokaryotic DNA is not
- Differences in base sequences
- Differences in histones/interaction with histones
- Differences in condensation/(super)coiling
- Different genes
In Figure 2 the chromosomes are arranged in homologous pairs.
What is a homologous pair of chromosomes? (1)
(Two chromosomes that) carry the same genes
Give the two types of molecule from which a ribosome is made (1)
(r)RNA and protiens
Describe the role of a ribosome in the production of a polypeptide. Do not
include transcription in your answer (3)
- mRNA binds to ribosome
- Idea of two codons / binding sites
- (Allows) tRNA with anticodons to bind / associate
- (Catalyses) formation of peptide bond between amino acids
- Moves along (mRNA to the next codon)
There is genetic diversity within HPV. Give two ways doctors could use base sequences to compare different types of HPV (2)
- Compare (base sequences of) DNA
- Look for mutations/named mutations
- Compare (base sequences of) (m)RNA
Describe how mRNA is produced in a plant cell (5)
- The DNA strands separate by breaking the H bonds / H bonds broken between (complementary) (DNA) bases
- (Only) one of the strands/template strand is used (to make mRNA/is transcribed)
- (Complementary) base pairing so A→U, T→A, C→G, G→C
(RNA) nucleotides joined by RNA polymerase - pre-mRNA formed
- Splicing / introns removed to form mRNA;
Starting with mRNA in the cytoplasm, describe how translation leads to the box production of a polypeptide. Do not include descriptions of transcription and splicing in your answer (5)
- . mRNA associates with a ribosome / ribosome attaches to mRNA
- Ribosome moves to / finds the start codon / AUG
- tRNA brings / carries (appropriate / specific) amino acid
- Anticodon (on tRNA complementary) to codon (on mRNA)
- Ribosome moves along to next codon
- . (Process repeated and) amino acids join by peptide bonds / condensation reaction (to form polypeptide) / (Process repeated and) amino acids joined using (energy from) ATP (to form polypeptide)
Compare and contrast the DNA in eukaryotic cells with the DNA in prokaryotic cells (5)
