More about the Nucleus

Nucleus Nuclear envelope - a double membrane that separates the nucleus from the cytoplasm Nuclear pores - numerous openings in the nuclear envelope, control movement of substances between nucleus and cytoplasm Nucleolus - spherical body that produces ribosomes

DNA DNA is found in chromosomes (in cells prepared for division) or in chromatin (in nondividing cells) In addition to DNA, chromosomes contain proteins histones Gene = segment of DNA coding for a protein; info is stored in the sequence of nitrogenous bases Fig. 3.20

A T T A G C C G G C TATA T A G C C G G C T A A T Packaging DNA Histone proteins Histone octomer DNA Helix 2 nm

A T T A G C C G G C TATA T A G C C G G C T A A T Packaging DNA Histone proteins DNA Helix Histone octomer 2 nm

A T T A G C C G G C TATA T A G C C G G C T A A T Packaging DNA Histone proteins Histone octomer Nucleosome 11 nm DNA Helix 2 nm

Packaging DNA A T T A G C C G G C T A A T

Packaging DNA A T T A G C C G G C T A A T

Packaging DNA A T T A G C C G G C T A A T 11 nm “Beads on a string” 30 nm Tight helical fiber Looped Domains 200 nm

Packaging DNA G C A T Chromosome 700 nm 11 nm 30 nm 200 nm 2 nm Looped Domains Nucleosomes DNA Helix Tight helical fiber

Karyotype = collection of all organism’s chromosomes

Body & Sex Chromosomes

So why is DNA the boss? Carries info for synthesis of proteins Study fig. 3.21, 3.22, 3.23 Protein synthesis movie

So how does the info from DNA get into the cytoplasm? With the help of RNA (ribonucleic acid) The big picture: DNA → RNA→ protein PROTEIN SYNTHESIS (Gene Expression): Part I: Transcription: DNA → RNA (in the nucleus) Part II: Translation: RNA → amino acids (in the cytoplasm on ribosomes)

Part I: How do cells make RNA? Transcription = DNA → RNA (using the DNA sequence to make RNA) Takes place in the nucleus

Steps of Transcription 1.Enzymes “unzip” the DNA molecule 2.Free RNA nucleotides pair with complementary DNA nucleotides 3.RNA breaks away and leaves the nucleus, DNA strands rejoin

Part II: How do cells make proteins? Translation = RNA → amino acids 3 types of RNA function in translation: 1.mRNA (messenger RNA) – carries info from DNA to ribosomes in a three letter genetic code = codon 2.tRNA (transfer RNA) – brings specific amino acids to ribosomes by matching mRNA; 3 nitrogenous bases that are complementary to codon = anticodon 3.rRNA (ribosomal RNA) – makes up ribosomes

ala met arg ile Steps of Translation 1.The start codon of mRNA attaches to the ribosome 2.tRNA brings aa to the ribosome; matching its anticodon to codon of mRNA 3.Ribosome moves along to the next mRNA codon and new tRNA brings in a second aa 4.Peptide bond forms between the 1 st aa and 2 nd aa 5.As the process continues, a chain of aa is formed until the ribosome reaches a stop codon Peptide bond

A TYPICAL PROTEIN Remember: proteins are made of amino acids The 20 amino acids make up all proteins There is redundancy in the genetic code: more than one codon can code for the same aa

A U G CGAUUCCCA A A A A U U U U U G GGG G G G G G G C C ile met pro stop pro his Anticodon codon Codon Chart

transcription translation mRNA