StemUp: AQA A level Biology 3.4.1 DNA, genes and chromosomes

Describe the properties of the DNA molecules present in prokaryotic cells (3)

- Short

- Circular

- Not associated with proteins

Describe the properties of the DNA molecules present in eukaryotic cells (3)

- Very long

- Linear

- Associated with histones (a protein)

How are chromosomes formed? (2)

DNA + histones join together

Compare the DNA present in prokaryotic cells with the DNA present in eukaryotic cells (6)

Please use comparative terminology when comparing!!

NOTE: The DNA in mitochondria and chloroplasts possess similar properties to‏‏‎ ‎‏‏‎the DNA in‎‏‏‎ ‎‏‏‎‏‏prokaryotic cells

What is a gene? (3)

- A sequence of DNA bases

- Which code for the specific amino acid sequence of a polypeptide

- And code for functional RNA e.g. ribosomal RNA and tRNAs

What is meant by a 'locus'? (2)

- Fixed position that a gene occupies

- On a particular DNA molecule or chromosome

What is a base triplet in DNA? (2)

- A sequence of three nucleotide bases

- That code for a specific amino acid

What are codons? (1)

Base triplets in mRNA

What is the genetic code? (1)

The instructions contained in a gene that tell a cell how to make a specific protein

NOTE: this is not a definition that you need to memorise, you just have to understand it for application based questions

What are the three features of the genetic code? (3)

- Degenerate

- Non-overlapping

- Universal

Describe the 'degenerate' feature of the genetic code (1)

More than one triplet could code for the same amino acid

Describe the 'non-overlapping' feature of the genetic code (1)

Each base is only read once as part of a specific triplet

Describe the 'universal' feature of the genetic code (1)

The same triplet codes for the same amino acids in all organisms

What are introns? (2)

- Non-coding part of a gene

- Base sequences present within genes but do not code for amino acids

What are multiple repeats? (3)

- Non-coding part of a gene

- Some of the base sequences present between genes

- That consists of the same base sequence occurring again and again

What are exons? (2)

- Coding part of a gene

- Base sequences in genes that code for amino acids

Describe how exons and introns are related to each other in a DNA sequence (2)

In the DNA sequence (top sequence), exons are separated by introns