SBI 3U
The Structure and Replication of the Genetic Material
In sexually reproducing species, offspring obtain a unique combination of genetic information
from their parents. How is this different from organisms that reproduce asexually?
______________________________________________________________________________
______________________________________________________________
The Genetic Material
DNA or __________________________________________________
Where is it found? _________________________________________
DNA is organized into ________________________
Genes are units of inherited information that carry a code for __________________________
____________________________________________________
Many genes code for _____________________
The information contained in genes is responsible for_______________________.
Packaging of DNA
For much of a cell's life, its DNA exists as a mass of very long, thin fibres called ___________ ,a
combination of _______________________________.
As a cell is preparing to divide, its chromatin fibres condense, becoming visible compact
structures called chromosomes.
A ___________________________ consists of one long, condensed DNA molecule containing
hundreds or thousands of __________________. The number of chromosomes inside a body
cell varies among different species. We call this the
__________________________ (or 2n).
(Humans 2n = 46, fruit flies 2n =8 etc.)
DNA consists of a long chain of subunits called
_______________________. A nucleotide has three parts:
1) A ring-shaped sugar called deoxyribose
2) A phosphate group
3) A nitrogenous base (or base): a single or double ring of carbon
& nitrogen atoms.
There are four types of nucleotides in DNA, which differ only in their
nitrogenous bases (thymine (T), adenine (A), cytosine (C) & guanine (G).
Scientists discovered that there are bonds between specific base pairs that
provide enough force to hold the two strands in the helix together. It is the
placement of these bonds that twists DNA into a spiral shape. A pairs with T; C
pairs with G.
DNA Sequences
We use the 26 letters of the alphabet to spell an almost countless number of words. Like letters
of the alphabet, nucleotides can combine in various sequences. Since nucleotide chains also
vary in length, from a few hundred to millions of nucleotides, the number of possible
nucleotide sequences is essentially unlimited.
The arrangement of nucleotides in DNA stores information.
The genes in this information code for specific cell proteins and functions.
The Cell Cycle: Two main stages:
1) Interphase
- the growing stage, cell carries out its metabolic processes, performs regular cellular activities
- DNA is duplicated, centrioles replicate
- the cell spends most of its time (90%)
Chromatid - a “chromosome” attached to another “chromosome” by a centromere.
2) Mitotic phase
- mitosis (cell division); the nucleus and the duplicated chromosomes divide and are evenly
distributed between two "daughter" nuclei
- cytokinesis - division of the cytoplasm (usually begins before mitosis is complete)
Three Reasons why we need mitosis:
1) ______________________________________________________________
2) ______________________________________________________________
3) ______________________________________________________________
The Four Phases of Mitosis:
1) Prophase
- the start of mitosis
- double chromosomes attached at the centromere become visible under a microscope and can
each be called a _______________________
- chromosomes ______________________ (get shorter and thicker)
- spindle fibers start to ________________
- spindle fibers: protein structures that __________________ chromosomes during cell division.
2) Metaphase
- The double chromosomes are lined up on the _________________ and separate so that one
chromatid from each pair goes towards a ___________________________________.
- when the chromatids separate they are called __________________________.
3) Anaphase
- the chromosomes, assisted by the spindle fibres move towards the _____________. Each pole
will get an identical set of chromosomes.
4) Telophase
- last stage of mitosis, begins when chromosomes reach the poles.
- chromosomes elongate, uncoil and assume the threadlike appearance of ________________.
- the spindle _______________________.
- nuclear __________________________ form
- nucleolus (nucleoli) _______________________
Cytokinesis in Animal Cells:
- aka - division of the cytoplasm
- the cell membrane pinches together
(forms cleavage furrow) starting in late anaphase and ending in telophase
Cytokinesis in Plant Cells:
- a cell plate forms in the middle of the dividing cell and extends out to connect with the
existing cell wall.
- cell wall is secreted out from each newly formed cell
…the cycle begins again.
Work: p.90 #1-4, 6-8 + 10, 11