The Cell Cycle Part 1

DNA

Science 9

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Recap: Cell Structure

What is the function of the Nucleus?

• The nucleus is the control centre of the cell

• It directs and controls all of the cell’s activities which includes growing, developing, and replicating

Grow Up!

Where is the nucleus?

What do you notice about it’s structure?

What is DNA?• The instructions for the cell’s activities are located

in the nucleus and carried in molecules of DNA

• DNA is a long, two-stranded molecule with a shape like a ladder that has been twisted into a spiral

• DNA stands for Deoxyribonucleic Acid

• Side of DNA Ladder = Phosphates and Sugar

• Middle = Nitrogen Bases 1) Adenine (A)2) Thymine (T)3) Cytosine ( C )4) Guanine (G)

Rules: Remember where they’re “AT”A always pairs with TC always pairs with G• This is called complimentary base pairing

What is the Structure of DNA?

a.k.a.Nucleotides

If you know a sequence of nitrogen bases on one half of the ladder, you can fill in the other half of the ladder using the idea of complimentary base pairing

Example) Let’s say one side of a DNA ladder has this sequence of bases:

A T C G G A C G T

Complimentary Base Pairing

Other Side: T A G C C T G C A

DNA makes Chromatin & Chromosomes• DNA stores genetic material• information that is passed on from one generation to

another during reproduction

• DNA is usually stored in the nucleus in the form of chromatin à messy silly string• DNA molecule and proteins together

• Before a cell needs to divide, the chromatin gets more organized into compact structures called chromosomes• Humans have a total of 46 chromosomes in each body

cell (= 23 pairs)

Most of the time

For Cell Division

What are Genes?

• Genes are found at specific places on a chromosome

• Genes are small segments of DNA that have the instructions for making proteins

• Proteins are made in the cell by ribosomes (organelles)

• Ribosomes are made in the nucleolus and come out of the nuclear pores à go into the cytoplasm or on the E.R.

One HALF of an “X” is a chromosome. The other half is a copy of that same chromosome.

Gene Vs. Chromosome

A centromereholds the two identical chromosomes together.

Recap of Cell Structure & DNA

Biology Cell Structure Video:

• https://youtu.be/8IlzKri08kk?t=191

Check your understanding

1. Why are Proteins so Important? What do they do in our bodies?

BC Science 9 p. 129 - 130

2. 4.1 CYU questions

BC Science 9 p. 135 #1-16