3.4 Genetic information, variation and relationships between organisms Flashcards
3.4.1 DNA, Genes and Chromosomes
How is DNA associated in prokaryotic cells?
- DNA is short
- DNA is circular
- DNA is not associated with proteins
How is DNA associated in eukaryotic cells?
- found in the nucleus
- DNA molecules are very long
- DNA is linear
- DNA is associated with proteins, called histones.
What do DNA molecules and its associated proteins form?
- A chromosome
What other subcellular structures in a eukaryotic cell contain DNA and how is it associated in these structures?
- chloroplasts
- mitochondria
- the DNA is associated like the DNA in a prokaryotic cell; short, circular and not associated with proteins
What is a gene?
- A gene is a base sequence of DNA that codes for the amino acid sequence of a polypeptide and a functional RNA
What is a locus?
- when gene occupies a fixed position on a particular DNA molecule.
What is a triplet?
- A sequence of three DNA bases which codes for a
specific amino acid.
Give three features of the genetic code
- universal
- non-overlapping
- degenerate.
What is meant by ‘universal’?
- all species use the same four bases A,T,C and G
- each base sequence codes for the same amino acid in all species
What is meant by ‘non-overlapping’?
- each triplet is only read once
- triplets don’t share any bases.
What is meant by ‘degenerate’?
- more than one triplet codes for the same
amino acid - this reduces the number of mutations
What are exons?
- A sequence of DNA that codes for an amino acid sequence.
What are introns?
- non-coding regions of the gene
- do not contain codons needed to make the final protein
- Introns are found in between exons.
3.4.2 DNA and Protein Synthesis
Define the term ‘genome’
- the complete set of genes in a cell
Define the term ‘proteome’
- the full range of proteins that a cell is able to produce.
What is RNA made up of?
- RNA nucleotides are ribose
- a phosphate group
- and one of the four bases adenine, cytosine, guanine or uracil
Describe the structure of RNA
- Contains pentose sugar ribose
- it is single stranded
- Contains uracil instead of thymine
- is a relatively short polynucleotide chain.
What is DNA made up of?
- DNA nucleotides are deoxyribose
- a phosphate group
- one of the organic bases adenine, cytosine, guanine or thymine.
Describe the structure of DNA?
- contains pentose sugar deoxyribose
- is double stranded
- thymine paired with adenine
- long
- double helix composed of two polynucleotides joined together by a hydrogen bonds
Describe the structure of tRNA
- small molecule made up of around 80 nucleotides.
- It is single stranded
- folded into a clover leaf shape in which one end extends from the others. (here an amino acids
attaches). - At the opposite end is an anticodon which is specific to the amino acid that the tRNA attaches to.
Describe the structure of mRNA
- this is a long single strand
- created during transcription
- the base sequence is complementary to DNA.
- Each set of three bases, called the codon, match a triplet on the DNA as well as the tRNA.
Describe the process of transcription
- The DNA helix unwinds to expose the bases to acts as a template
- Only one chain of the DNA acts as a template
- This unwinding an unzipping is catalysed by DNA helicase
- DNA helicase breaks the hydrogen bonds between bases
- Free mRNA nucleotides in the nucleus align opposite exposed complementary DNA bases
- The enzyme RNA polymerase joins together the RNA nucleotides to create a new RNA polymer chain. One entire gene is copied
- Once copied, the mRNA is modified and then leaves the nucleus through the nucleur envelope pores
In prokaryotes, what does transcription result in the production of?
- transcription results directly in the production of mRNA from DNA.
In eukaryotes, what does transcription result in the production of?
- results in the production of premRNA;
- this is then spliced to form mRNA.