3.4.1

• Eukaryotic DNA is ?

  1.Long

  2. linear

  3. associated with proteins called histones, and tightly coiled into chromosomes

  4.contains introns
• Prokaryotic DNA is ?

  • short, circular, and not associated with proteins/histones.
  • does not contain Introns
• Mitochondria and chloroplasts in eukaryotic cells have their own DNA, which is similar to prokaryotic DNA in terms of being short, circular, and not associated with proteins/histones.
• A gene occupies a fixed position, called a locus, on a particular DNA molecules.
• The genetic code is a sequence of DNA triplets (or mRNA codons) that codes for the sequence of amino acids.
• DNA triplet: sequence of 3 bases coding for specific amino acid.
• Universal: the same specific DNA base triplets code for the same amino acids in all living organisms.
• Non-overlapping: each base can only be used once and in only one triplet

  .Each base is part of only one triplet so each triplet is read as a discrete unit
• Degenerate: the same amino acid can be coded for by more than one base triplet.
• In eukaryotes, much of the DNA doesn’t code for polypeptides.
• Within genes, only exons code for amino acid sequences, which are separated by one or more non-coding sequences, called introns.
• Genome: the complete set of genes in a cell, including those in mitochondria and/or chloroplasts.
• Alleles: different version (sequence of bases / triplets) of the same gene.
• Homologous pair of chromosomes: same size chromosomes with same genes, but different alleles.
• Eukaryotic genes contain exons (coding regions) and introns (non-coding regions).
• Pre-mRNA contains introns + exons
• what are the similarities between prokaryotic DNA and Eukaryotic DNA?

  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
• What is a gene ?

  Genes are a sequence of DNA bases that codes for the amino acid sequence of a polypeptide, a functional RNA such as ribosomal RNA and tRNAs, or a functional protein.

  
• What is a chromosome?

  ● Long, linear DNA + its associated histone proteins

  ● In the nucleus of eukaryotic cells

  
• What are ‘non-coding base sequences’ and where are they found?

  DNA that does not code for an amino acid sequence

  1. Between genes - eg. non-coding multiple repeats
  2. Within genes - introns -----In eukaryotes, much of the nuclear DNA does not code for polypeptides.
• Exam insight: common mistakes ❌( 1/6)

  ❌-“Bacteria / prokaryotic cells have chromosomes.”

  E: Chromosomes are found in eukaryotic cells. Bacteria have small, circular DNA not associated with histones.
• Exam insight: common mistakes ❌( 2/6)

  ❌-“Prokaryotic DNA is single stranded, and contains uracil instead of thymine.

  E: -This describes RNA. Prokaryotic DNA is double stranded and made of exactly the same nucleotides as eukaryotic DNA (with A, T, C, G).
• Exam insight: common mistakes ❌( 3/6)

  ❌-“Triplets produce amino acids.”

  E: Triplets code for amino acids, but don’t directly produce them
• Exam insight: common mistakes ❌( 4/6)

  ❌-“A gene is a section of DNA that codes for proteins.”

  E: -This is too vague. A gene is a sequence of DNA (nucleotide) bases that codes for a polypeptide (or functional RNA).
• Exam insight: common mistakes ❌( 5/6)

  ❌-“An intron is a non-coding region of a gene.”

  E: -This is correct, but not enough to get a mark. You must state what it is that introns don’t code for, ie. amino acids.
• Exam insight: common mistakes ❌( 6/6)

  ❌-“An exon codes for a protein.”

  E: -This is too vague. An exon is a base sequence of a gene coding for amino acid sequences (in a polypeptide).