Cell Cycle and Cell Differentiation: Phases and Functions

1. KEY CONCEPT Cells have distinct phases of growth, reproduction, and normal functions.

2. The cell cycle has four main stages. • The cell cycle is a regular pattern of growth, DNA replication, and cell division.

3. The main stages of the cell cycle are gap 1, synthesis, gap 2, and mitosis. • Gap 1 (G1): cell growth and normal functions • DNA synthesis (S): copies DNA • Gap 2 (G2): additional growth • Mitosis (M): includes division of the cell nucleus (mitosis) and division of the cell cytoplasm (cytokinesis) • Mitosis occurs only if the cell is large enough and the DNA undamaged.

4. Cells divide at different rates. • The rate of cell division varies with the need for those types of cells. • Some cells are unlikely to divide (G0).

5. Cell size is limited. • Volume increases faster than surface area.

6. Surface area must allow for adequate exchange of materials. • Cell growth is coordinated with division. • Cells that must be large have unique shapes.

7. KEY CONCEPT Cells work together to carry out complex functions.

8. SYSTEMS leaf shoot system stem vascular tissue CELL TISSUE ORGAN root system lateral roots primary root Multicellular organisms depend on interactions among different cell types. • Tissues are groups of cells that perform a similar function. • Organs are groups of tissues that perform a specific or related function. • Organ systems are groups of organs that carry out similar functions.

9. Inner: intestines Outer: skin cells Middle: bone cells Specialized cells perform specific functions. • Cells develop into their mature forms through the process of cell differentiation. • Cells differ because different combinations of genes are expressed. • A cell’s location in an embryo helps determine how it will differentiate.

10. Stem cells are unique body cells. • Stem cells have the ability to • divide and renew themselves • remain undifferentiated in form • develop into a variety of specialized cell types

11. totipotent, or growing into any other cell type • pluripotent, or growing into any cell type but a totipotent cell • multipotent, or growing into cells of a closely related cell family • Stem cells are classified into three types.

12. First, an egg is fertilized by a sperm cell in a petri dish. The egg divides, forming an inner cell mass. These cells are then removed and grown with nutrients. Scientists try to control how the cells specialize by adding or removing certain molecules. • Adult stem cells can be hard to isolate and grow. • The use of adult stem cells may prevent transplant rejection. • The use of embryonicstem cells raisesethical issues • Embryonic stem cellsare pluripotent andcan be grown indefinitelyin culture. • Stem cells come from adults and embryos.

13. The use of stem cells offers many currently realized and potential benefits. • Stem cells are used to treat leukemia and lymphoma. • Stem cells may cure disease or replace damaged organs. • Stem cells may revolutionize the drug development process.

14. KEY CONCEPT DNA was identified as the genetic material through a series of experiments.

15. Griffith finds a ‘transforming principle.’ • Griffith experimented with the bacteria that cause pneumonia. • He used two forms: the S form (deadly) and the R form (not deadly). • A transforming material passed from dead S bacteria to live R bacteria, making them deadly.

16. Avery identified DNA as the transforming principle. • Avery isolated and purified Griffith’s transforming principle. • Avery performed three tests on the transforming principle. • Qualitative tests showed DNA was present. • Chemical tests showedthe chemical makeupmatched that of DNA. • Enzyme tests showedonly DNA-degradingenzymes stoppedtransformation.

17. Hershey and Chase confirm that DNA is the genetic material. • Hershey and Chase studied viruses that infect bacteria, or bacteriophages. • They tagged viral DNA with radioactive phosphorus. • They tagged viral proteins with radioactive sulfur. • Tagged DNA was found inside the bacteria; tagged proteins were not.

18. KEY CONCEPT Transcription converts a gene into a single-stranded RNA molecule.

19. RNA carries DNA’s instructions. • The central dogma states that information flows in one direction from DNA to RNA to proteins.

20. replication transcription translation • The central dogma includes three processes. • Replication • Transcription • Translation • RNA is a link between DNA and proteins.

21. RNA differs from DNA in three major ways. • RNA has a ribose sugar. • RNA has uracil instead of thymine. • RNA is a single-stranded structure.

22. Transcription makes three types of RNA. • Transcription copies DNA to make a strand of RNA.

23. transcription complex start site nucleotides • Transcription is catalyzed by RNA polymerase. • RNA polymerase and other proteins form a transcription complex. • The transcription complex recognizes the start of a gene and unwinds a segment of it.

24. DNA RNA polymerase moves along the DNA • Nucleotides pair with one strand of the DNA. • RNA polymerase bonds the nucleotides together. • The DNA helix winds again as the gene is transcribed.

25. RNA • The RNA strand detaches from the DNA once the gene is transcribed.

26. Transcription makes three types of RNA. • Messenger RNA (mRNA) carries the message that will be translated to form a protein. • Ribosomal RNA (rRNA) forms part of ribosomes where proteins are made. • Transfer RNA (tRNA) brings amino acids from the cytoplasm to a ribosome.

27. one gene growing RNA strands DNA The transcription process is similar to replication. • Transcription and replication both involve complex enzymes and complementary base pairing. • The two processes have different end results. • Replication copiesall the DNA;transcription copiesa gene. • Replication makesone copy;transcription canmake many copies.

28. KEY CONCEPT Translation converts an mRNA message into a polypeptide, or protein.

29. codon for methionine (Met) codon for leucine (Leu) Amino acids are coded by mRNA base sequences. • Translation converts mRNA messages into polypeptides. • A codon is a sequence of three nucleotides that codes for an amino acid.

30. The genetic code matches each RNA codon with its amino acid or function. • The genetic code matches each codon to its amino acid or function. • three stop codons • one start codon, codes for methionine

31. A change in the order in which codons are read changes the resulting protein. • Regardless of the organism, codons code for the same amino acid.

32. Amino acids are linked to become a protein. • An anticodon is a set of three nucleotides that is complementary to an mRNA codon. • An anticodon is carried by a tRNA.

33. Ribosomes consist of two subunits. • The large subunit has three binding sites for tRNA. • The small subunit binds to mRNA.

34. For translation to begin, tRNA binds to a start codon and signals the ribosome to assemble. • A complementary tRNA molecule binds to the exposed codon, bringing its amino acid close to the first amino acid.

35. The ribosome helps form a polypeptide bond between the amino acids. • The ribosome pulls the mRNA strand the length of one codon.

36. The now empty tRNA molecule exits the ribosome. • A complementary tRNA molecule binds to the next exposed codon. • Once the stop codon is reached, the ribosome releases the protein and disassembles.