T4: Genetic Information & Variation Flashcards
What are the components of nucleotides?
- pentose sugar
- phosphate group
- an organic nitrogenous base
Describe how a phosphodiester bond is formed between two nucleotides within a DNA
molecule. (2)
- Condensation (reaction)/loss of water;
- (Between) phosphate and deoxyribose;
- (Catalysed by) DNA polymerase;
In the process of semi-conservative DNA replication, the two strands within a DNA molecule are separated. Each then acts as a template for the formation of a new complementary strand.
Describe how the separation of strands occurs. (2)
- DNA helicase;
- Breaks hydrogen bonds between base pairs/ AT and GC/complementary bases
OR
Breaks hydrogen bonds between polynucleotide strands;
Reject hydrolysis of hydrogen bonds
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:
1. DNA shorter;
Accept smaller
2. Fewer genes;
3. DNA circular not linear;
4. Not associated with protein/histones, unlike nuclear DNA;
5. Introns absent but present in nuclear DNA;
Must be comparative statements.
DNA is a polymer of nucleotides. Each nucleotide contains an organic base.
Explain how the organic bases help to stabilise the structure of DNA. (2)
- Hydrogen bonds between the base pairs holds two strands together
- Many hydrogen bonds provides strength
Describe FOUR differences between the structure of a tRNA molecule and the structure of an
mRNA molecule. (4)
- 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;
Accept ‘CCA end’ for amino acid binding site - tRNA has anticodon, mRNA has codon;
Must be a comparison
what is a codon?
- triplets of bases that code for a particular amino acid
What is the genetic code?
- the order of bases on DNA
- ## consitsts of codons ( triplets of bases that code for a particular amino acid)
Why is the genetic code described as being universal? (1)
- (In all organisms / DNA,) the same triplet codes for the same amino acid;
Define a gene
- a base sequence of DNA that codes for the amino acid sequence of a polypeptide or a functional RNA molecule
give the functions of the three types of RNA.
mRNA - the bases are used by ribosomes to form polypeptide chains
tRNA - carries amino acids to the ribosome
rRNA - ribosomal RNA molecules form part of the structure of ribosomes
Identify and define features of the genetic code.
- non-overlapping : each triplet is only read once / each base is part of only one triplet
- degenerate: more than one triplet codes for the same amino acid.
- Universal = the same triplet codes for the same amino acid in all species
1, E.g. ACA ATA not CAA TA or AAT
What is a locus?
- fixed position on a DNA molecule occupied by a gene
What is an allele?
- different versions of the same gene found at the same locus on a chromosome.
Define exons and introns
exons: Base/ triplet sequence coding for polypeptide/sequence of amino acids
Introns: regions of DNA that do not code for anything. ( non-coding DNA)
exons: regions of DNA that code for amino acid sequences
Where are introns found?
- between exons
- within genes
Describe how a gene is a code for the production of a polypeptide. Do not
include information about transcription or translation in your answer
- Because base/nucleotide sequence;
- In triplets;
- (Determines) order/sequence of amino acid /primary structure (in polypeptide);
Compare and contrast the DNA in eukaryotic cells with the DNA in prokaryotic cells (5)
give similarities also!!
- 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;
Not all mutations in the nucleotide sequence of a gene cause a change in the structure of a polypeptide. (2) Give two reasons why.
- Triplets code for same amino acid
Accept: DNA/code/triplets are degenerate
Reject: codons (as question states within genes) - Occurs in introns /non-coding sequence;
Define the terms:
genome
proteome
genome: the complete set of genetic information contained in the cells of an organism
proteome: full) range of / number of different proteins that a cell is able to produce/ DNA is able
to code for (at a given time)
Describe the structure of mRNA.
- long , linear , single strand.
- It is made up of a sugar-phosphate backbone and exposed unpaired bases
- Uracil bases are present instead of thymine bases
Suggest the advantages of using mRNA rather than DNA for translation
- shorter & contains uracil so no excess polypeptide forms
- single-stranded & linear = ribosome moves along strand & tRNA binds to exposed bases
- contains no introns
Describe the structure of tRNA
- tRNA is a single-stranded molecule
- It has a sugar-phosphate backbone
- It has a folded , CLOVER LEAF shape
- has anticodon complemenrary to codon on MRNA
- has amino acid binding site
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.
- mRNA has fewer nucleotides
Pre-mRNA more nucleotides
OR
mRNA has no introns/has (only) exons
OR
Pre-mRNA has (exons and) introns; - (Because of) splicing
Accept mRNA is shorter OR pre-mRNA is longer