Cell Growth and Division Ms. Hughes

Why Cells Reproduce Multicellular organisms grow larger by producing more cells. New cells are needed to keep organisms healthy and replace old worn out cells. 3 main reasons for cells to reproduce

#1:Cell Size Larger cells require more nutrients Smaller cells are easier to maintain

#2:Cell maintenance More proteins (signals) are required to keep a larger cell up and running (protein synthesis). Smaller cells require less proteins.

#2:Cell maintenance If a cell gets larger DNA cannot be copied quickly enough for that cell to continue dividing. DNA limits a cell’s size.

#3:Making New Cells “Daughter” cells have a higher surface area-to-volume ratio than it’s parent does. Because larger cells are more difficult to maintain, cells divide when they grow to a certain size.

Prokaryotic Chromosomes Single circular loop/molecule of DNA Thousands of genes on this molecule Condensed like a rubber band coiling back onto itself.

Eukaryotic Chromosomes Linear chromosomes Much more genes than prokaryotes. Eukaryotic DNA is packaged into highly condensed chromosome structures with the help of many proteins DNA and chromosomes make up chromatin.

Forms of chromatin Histones ( a protein) allow DNA to wrap around them like a spool of thread. Once DNA has wrapped around the histone this is now called a nucleosome. Nucleosomes line up together to form a chord.

Packaging During Cell Division For most of its life the cell’s DNA remains in this chord of nucleosomes. During cellular division the chord condenses even farther to ensure that the DNA is not damaged and is copied properly during cellular replication and division.

Preparing for cell division All cells come from pre-existing cells DNA is copied before the cell is replicated and divides All newly-formed cells require DNA, so before a cell divides a copy of DNA is made for each daughter cell

Prokaryotes The cell grows larger The DNA strand is doubled like a rubber band. The cell is pinched in the middle like a balloon animal.

Eukaryotes Eukaryotic cellular reproduction is much more complicated because they contain more DNA, organelles and are more complex themselves.

Mitosis Mitosis is the division of a cell’s nucleus. There are several steps that must be complete before this can happen however

Eukaryotic Cell Cycle Cell cycle: is a sequence of cellular growth and division during the life of a cell. The life of a eukaryotic cell cycles through phases of: Growth DNA replication preparation for cell division division of the nucleus and cytoplasm.

Interphase Composed of three separate phases: G1, S, and G2 During interphase the cell is not dividing. The cell is growing and preparing to divide. Some cells divide often and others do not.

Cell Division Mitosis Cytokinesis

Cytokinesis During cytokinesis, the cell membrane grows into the center of the cell and divides it into two daughter cells of equal size. Each daughter cell has about half of the parent’s cytoplasm and organelles.

Controls Cell growth and division depend on protein signals and other environmental signals. Available nutrients Size of cells Etc.

Checkpoints Doodle defs for the 3 checkpoints G1 check point – checks to make sure cell and organelles have grown to proper size. G2 check point – Cell checks to make sure DNA is copied correctly Mitosis – cell checks to make sure sister chromatids lined up correctly so that when they are pulled apart in anaphase each cell gets one chromosome.