1

The cell cycle, DNA,and protein synthesis

• We will becovering bitsand pieces ofCh. 19 (the cellcycle) and Ch.21 (DNA andproteinsynthesis)

Cell division• = the reproduction of cells• 1. Mitosis produces somatic cells (= all body cells except sex cells• 2. Meiosis produces sex cells (= ♂ sperm and ♀ eggs)

– We’ll cover meiosis with the reproductive system chapter

The cell cycle2 main parts:• 1. Interphase –

normal cellfunctions; prepfor cell division(e.g. DNAreplication)– Most somatic

cells spendmajority of livesin interphase(durationvaries bycell type)

• 2. Cell division/mitosis

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Overview of mitosis

Stages of cell division(mitosis) – continued on next slide

Stages of cell division (mitosis), continued

Cytokinesis• = division of cytoplasm after mitosis; last stage of cell division

3

Review ofDNA

structure…

• …so that we can betterunderstand DNA replicationand protein synthesis

• Remember, for DNA:– A is complementary to T– C is complementary to G

DNA replication

• Occurs during the “S”(middle) part ofinterphase of the cellcycle

• DNA polymerases =enzymes that link theadjacent nucleotidesof each new(complementary)strand

Gene expression is protein synthesis

• Gene = a segment of DNA that contains a sequence ofnucleotide bases that codes for a specific polypeptide orprotein

• Transcription: information stays in the same language(nucleotide base sequence)– Takes place in nucleus

• Translation: information is translated from nucleotide basesequence to amino acid sequence– This is the actual “protein synthesis” part this whole process– Takes place in cytoplasm

transcription translationDNA mRNA protein(gene)

Needs for protein synthesis• 1. Instructions:

– Genes on DNA in nucleus

• 2. An assembly site:– Ribosomes (which are made up of rRNA + proteins) in cytoplasm

• 3. A courier:– mRNA (messenger RNA) takes instructions from nucleus to assembly

site in cytoplasm

• 4. Raw materials:– Amino acids in cytoplasm

• 5. Transport of raw materials to assembly site:– tRNA (transfer RNA) carries amino acids to ribosome

4

The genetic code• Codon = three (3) nucleotide bases in a specific sequence that code for

one amino acid• So a gene contains all the codons needed to code for a specific

polypeptide– May be hundreds or thousands of bases long

(mRNA codons)

Transcription• = making an mRNA copy of a DNA gene in the nucleus• RNA polymerase = the enzyme that makes it happen• The finished mRNA transcript will leave the nucleus and

travel to a ribosome in the cytoplasm

Translation• = assembling amino acids into

a polypeptide at the ribosomeaccording to the mRNAsequence

• Anticodon = 3 base sequenceof tRNA that is complementaryto a mRNA codon– Determines which amino acid

the tRNA can carry

• Remember, for RNA:– A is complementary to U– C is complementary to G

Ribosomes: the workbenches onwhich proteins are built (translation)

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Translation

Translation

Translation

Review: DNA vs. RNA

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Review: the 3 types of RNA