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Chapter 8

Biology Cell cycles chapter 8.docx

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Biology 1201A
Richard Gardiner

Biology Cell cycles chapter 8 Eukaryotic cells have the ability to divide making daughter cells with complete set of genetic material Cell cycle in prokaryotic cells Binary fission- the splitting of two cells From birth the cells grow a well before DNA replication (B period) then the chromosomes replicate and separate-to-separate sides(C) and the membrane pinches together between them and the daughter cells are formed (D) The DNA is a single circular chromosome of double stranded DNA, which is founded in the nucleoid Origin of replication- where the enzymes of DNA replication are Cytokinetic ring- cytoplasmic division is involved with an inward constriction of a cytokinetic ring of cytoskeletal proteins DNA differences between prokaryotic and eukaryotic cells PRO EUK  Single chromosome  Several chromosomes greater length in DNA  Chromosomes contained in nuclear membrane  More lethal if daughter cells don’t receive chromosomes  In higher eukaryotes the nuclear membrane disappears and reforms around two new daughter cells  Double stranded DNA molecules that are combine with proteins that stabilize and help package DNA during cell division  Have two copies of each chromosome in their nuclei  Chromosomes are diploid (46) haploid (23) humans  A set of chromosomes is a ploidy  Sister chromatids Two new identical molecules formed DNA replication  Chromatids – double stranded DNA molecules help keep track of long Chromosomes and move them to the cytoskeleton for proper time to Produce daughter cells Eukaryotic Cell Cycle Eukaryotic cells undergo mitosis by producing identical daughter cells Three stages/systems 1. Molecular checks and balances are made throughout the cell cycle 2. DNA synthesis replicates each chromosome perfectly into two 3. Motors of the cytoskeleton separate the copies into daughter cells Sister chromatids are held tighter in the centromere until mitosis separates them into daughter cells the equal distribution of daughter chromosomes to two cells is chromosome segregation  DNA synthesis creates two copies of the DNA molecules and remain attached to each other and are called sister chromatid  Since they are attached they are considered one chromosome  Before replication one chromosome has one DNA molecule and after one chromosome has two DNA molecules  Chromosome replication and serration creates a group of cells called a clone which are all identical Cell cycle  Internal regulation controls trigger each phase  Internal mechanisms regulate overall cycles and are subject to other cells or virus has well as signal molecules such as hormones growth and death factors  First phase is interphase- it is the long phase where the cell replicates its DNA for mitosis and cytokinesis.  Interphase begins when the daughter cell from a pervious cycle enters cytoplasmic growth called the G (gap) phase were the cell makes proteins and RNA but not nuclear DNA  Then when the cell is going to divide and DNA replication begins it undergoes the S phase were the cell duplicates chromosomes proteins and DNA  After the cell enters the G2 phase (no DNA synthesis) were the cell continues to grow and produce RNAs and proteins including those for mitosis  Interphase finishes and mitosis begins and all the chromosomes are loose but organized in the nucleus  Mitosis begins in five stages  Prophase- the chromosomes condense into rod like structures and the nucleus disappears and RNA synthesis shuts down. In the cytoplasm the mitotic spindle forms between the centrosomes as they start moving to opposite ends of the cell to form spindle poles the spindle develops as bundles of microtubules radiate from the spindle nodes  Prometaphase- nuclear envelop breaks down and bundles of spindle microtubules grow from centrosomes at opposing spindle poles toward the center of the cell  Metaphase- spindle microtubules move the chromosomes into alignment  Anaphase- spindle separates the two sister chromatids of each chromosome and moves them to opposite poles and are now called daughter cells and segregation is complete  Telophase- spindle disassembles chromosomes return to extend physical state nuclear membrane forms RNA transcription resumes and two new daughter cells are
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