Cell Replication : Cell Replication Dawn Drooger, RN
Organization of DNA : Organization of DNA Chromatin:
loosely coiled DNA (cells not dividing)
Chromosomes:
tightly coiled DNA (cells dividing)
Genetic Code : Genetic Code The chemical language of DNA instructions:
sequence of bases (A, T, C, G)
triplet code:
3 bases = 1 amino acid
KEY CONCEPT : KEY CONCEPT The nucleus contains chromotic material
DNA stores genetic instructions for proteins
Proteins determine cell structure and function
Protein Synthesis : Protein Synthesis Transcription:
copies instructions from DNA to mRNA (in nucleus)
Translation:
ribosome reads code from mRNA (in cytoplasm)
assembles amino acids into polypeptide chain
Protein Synthesis : Protein Synthesis Processing:
by RER and Golgi apparatus produces protein
mRNA Transcription : mRNA Transcription A gene is transcribed to mRNA in 3 steps:
gene activation
DNA to mRNA
RNA processing
Step 1: Gene Activation : Step 1: Gene Activation Uncoils DNA, removes histones
Start (promoter) and stop codes on DNA mark location of gene:
coding strand is code for protein
template strand used by RNA polymerase molecule
Step 2: DNA to mRNA : Step 2: DNA to mRNA Enzyme RNA polymerase transcribes DNA:
binds to promoter (start) sequence
reads DNA code for gene
binds nucleotides to form messenger RNA (mRNA)
mRNA duplicates DNA coding strand, uracil replaces thymine
Step 3: RNA Processing : Step 3: RNA Processing At stop signal, mRNA detaches from DNA molecule:
code is edited (RNA processing)
unnecessary codes (introns) removed
good codes (exons) spliced together
triplet of 3 nucleotides (codon) represents one amino acid
Translation (1 of 6) : Translation (1 of 6) mRNA moves:
from the nucleus
through a nuclear pore Figure 3–13
Translation (2 of 6) : Translation (2 of 6) mRNA moves:
to a ribosome in cytoplasm
surrounded by amino acids Figure 3–13 (Step 1)
Translation (3 of 6) : Translation (3 of 6) mRNA binds to ribosomal subunits
tRNA delivers amino acids to mRNA Figure 3–13 (Step 2)
Translation (4 of 6) : Translation (4 of 6) tRNA anticodon binds to mRNA codon
1 mRNA codon translates to 1 amino acid Figure 3–13 (Step 3)
Translation (5 of 6) : Figure 3–13 (Step 4) Translation (5 of 6) Enzymes join amino acids with peptide bonds
Polypeptide chain has specific sequence of amino acids
Translation (6 of 6) : Protein Synthesis: Sequence of Amino Acids in the Newly Synthesized Polypeptide PLAY Figure 3–13 (Step 5) Translation (6 of 6) At stop codon, components separate
KEY CONCEPT : KEY CONCEPT Genes:
are functional units of DNA
contain instructions for 1 or more proteins
KEY CONCEPT : KEY CONCEPT Mutation is a change in the nucleotide sequence of a gene:
can change gene function
Causes:
exposure to chemicals
exposure to radiation
mistakes during DNA replication
3 Stages of Cell Division : 3 Stages of Cell Division Body (somatic) cells divide in 3 stages:
DNA replication duplicates genetic material exactly
Mitosis divides genetic material equally
Cytokinesis divides cytoplasm and organelles into 2 daughter cells
Interphase : Interphase The nondividing period:
G-zero phase—specialized cell functions only
G1 phase—cell growth, organelle duplication, protein synthesis
S phase—DNA replication and histone synthesis
G2 phase—finishes protein synthesis and centriole replication
DNA Replication : DNA Replication Figure 3–24 DNA strands unwind
DNA polymerase attaches complementary nucleotides
Mitosis : Mitosis Mitosis divides duplicated DNA into 2 sets of chromosomes:
DNA coils tightly into chromatids
chromatids connect at a centromere
protein complex around centromere is kinetochore
Features of Prophase : Features of Prophase Nucleoli disappear
Centriole pairs move to cell poles
Microtubules extend between centriole pairs
Nuclear envelope disappears
Spindle fibers attach to kinetochore
Features of Metaphase : Features of Metaphase Chromosomes align in a central plane (metaphase plate)
Features of Anaphase : Features of Anaphase Microtubules pull chromosomes apart
Daughter chromosomes groups near centrioles
Features of Telophase : Features of Telophase Nuclear membranes reform
Chromosomes uncoil
Nucleoli reappear
Cell has 2 complete nuclei
Long Life, Short Life : Long Life, Short Life Muscle cells, neurons rarely divide
Exposed cells (skin and digestive tract) live only days or hours
Normally, cell division balances cell loss
Factors Changing Cell Division : Factors Changing Cell Division Increases cell division:
internal factors (MPF)
extracellular chemical factors (growth factors)
Decreases cell division:
repressor genes (faulty repressors cause cancers)
worn out telomeres (terminal DNA segments)
KEY CONCEPT : KEY CONCEPT All body cells, except sex cells, contain the same 46 chromosomes
Differentiation depends on which genes are active and which are inactive