Section 4 : DNA, genes, chromosomes and protein synthesis Flashcards
What are some differences between eukaryotic and prokaryotic DNA?
- Eukaryotic: Long, linear, associated with proteins called histones, tightly coiled into chromosomes
- Prokaryotic: Short, circular, not associated with proteins
What is the DNA of prokaryotic cells similar to?
- Mitochondria and Chloroplast DNA
What is a gene?
- Sequence of DNA that codes for amino acid sequence in a polypeptide chain and functional RNA e.g ribosomal RNA and tRNA
What is a locus?
- When a gene occupies a fixed position on DNA molecules
What is the nature of genetic code?
- Universal: The same specific DNA base triplet codes for the same amino acids in all living organisms
- Non-overlapping: Discrete, each base can be used in 1 triplet/ read once
- Degenerate: The same amino acid can be coded for by more than 1 codon
In DNA what are the non-coding sections called?
Introns
What is the genome?
- The complete set of genes in a cell
What is the proteome?
- The full range of proteins that a cell/ genome can make
What are alleles?
- A version of a gene
What is a homologous pair?
- Same size chromosomes with same genes but different alleles
What are the 2 stages in protein synthesis?
- Transcription - produces mRNA from DNA in the nucleus
- Translation - produces polypeptides from codons carried by mRNA in the cytoplasm on ribosomes.
What is mRNA?
- Made by transcription in the nucleus
- Acts as a template for translation
- Straight chain molecule
- Chemically unstable - breaks down in few days
What is tRNA - transfer RNA?
- Carries an amino acid from amino acid binding site
- Anticodon complementary to codon
- Single polynucleotide strand - leafed clover shape
- Held together by hydrogen bonds
What is the similarity between mRNA and tRNA?
- Both single polynucleotide strand
What are the differences between mRNA and tRNA?
- mRNA - single helix, straight/ tRNA - clover shaped
- mRNA - longer, variable length/ tRNA - shorter
- mRNA - no paired bases or hydrogen bonds/ tRNA does
What is the process of transcription?
- Hydrogen bonds are broken by DNA helicase which separates the double helix
- RNA nucleotides bind by complementary base pairing
- RNA polymerase joins adjacent nucleotides together in a condensation reaction. Forming phosphodiester bonds
- When RNA polymerase reaches stop codon, pre-mRNA detaches from DNA
- Splicing removes introns - produces mRNA - leaves via nuclear pore
Does prokaryotic DNA have introns?
No
What is the process of translation?
- At the ribosome, tRNA anticodon binds to mRNA codon as it is complementary
- Brings the correct amino acid
- 2 amino acid joins in a condensation reaction forming a peptide bond - using ATP
- tRNA detaches, ribosome moves along to next codon.
- Continues until stop codon (polypeptide released)
What is the role of ATP in translation?
- Hydrolysis of ATP releases energy
- For the bond between the amino acid and its corresponding tRNA - amino acid attaches to amino acid binding site
- For peptide bond formation between amino acids
What is the role of tRNA in translation?
- tRNA attaches and transports a specific amino acid in relation to anticodon
- tRNA anticodon complementary base pairs to mRNA codon, forming hydrogen bonds
- 2 tRNAs bring amino acids for the formation of peptide bonds
- About 60 types of tRNA to carry 20 different amino acids - degenerate
What is the role of ribosomes in translation?
- Attaches to mRNA and houses tRNA, allowing codon-anticodon complementary base pairing
- Allows peptide bonds to form between amino acids
Exam Question: Ricin causes the death of cells and is very poisonous to many animals. Suggest how the action of ricin on ribosomes could cause the death of cells.(2)
- Prevents mRNA/tRNA binding
- Prevents formation of peptide bond
- Consequence of loss of identified protein
Exam Question: Ricin is found in high concentrations in the seeds of some species of plant. Suggest and explain 1 advantage of this to the plant.(2)
- Animals that can eat the plant get ill/ killed
- So seeds/plants more likely to survive
