1 of 7© Boardworks Ltd 2009. 2 of 7© Boardworks Ltd 2009 Warm Up: What are the four classes of macromolecules? Which class of macromolecules did we just

1 of 7 © Boardworks Ltd 2009


Warm Up:

• What are the four classes of macromolecules?

• Which class of macromolecules did we just finish studying?

• How are these formed? Where do our cells get the information to make these macromolecules?


In all living things, genetic information stored in DNA determines the traits of the organism and controls the activities of cells.

Passing on characteristics

What makes this baby human? What determines its gender? What directs its growth and development?

DNA can be copied and passed on to offspring, thereby passing on traits from parents to children.


Chromosomes and their genes are made of a molecule called DNA.

DNA molecules carry the code that controls what cells are made of and what they do.

DNA stands for deoxyribonucleic

acid.

Each chromosome is a very long molecule

of tightly coiled DNA.

Which part of a DNA molecule holds this information?

What is DNA?


The structure of DNA


How do you think the four bases are paired?

DNA and base pairs

There are four types of bases, and they are usually identified by their initials.

A

T

C

G

adenine

cytosine

guanine

thymine

The double helix ‘ladder’ of a DNA molecule is held together by ‘rungs’ made from pairs of chemicals called bases.


Base pairs hold the two strands of the DNA helix together.The rules for base pairing are…

There are millions of base pairs in a DNA molecule, and they always follow these rules.

‘A’ always pairs with ‘T’ ‘C’ always pairs with ‘G’

It is the sequence of these bases along a DNA molecule that forms the genetic code – it’s that simple!

How do bases pair together?

A T C G


Base pairing rules


Nucleotides: the “building blocks” of DNA

Nucleotides are nitrogen-containing organic substances that form the basis of the nucleic acids DNA and RNA.

All nucleotides contain the following three groups:

In DNA the sugar is deoxyribose, whereas in RNA the sugar is ribose.

a phosphate group

a pentose sugar

a nitrogen-containing base


Nucleotides and your DNA models

Nitrogen base + deoxyribose + 3 phosphates

Phosphate groups

Sugar (deoxyribose)

Nitrogen base (adenine, guanine, cytosine, or thymine)

Note: the previous image showed only 1 phosphate per nucleotide. Your pieces have only 1 phosphate group. But in a true DNA nucleotide, it would start with 3.


Formation of polynucleotides


Building a nucleotide chain: Two phosphates are removed to supply energy for the next step (a sugar-phosphate bond).


Forming a covalent bond between the sugar of one nucleotide and the phosphate of the other

Scotch tape(covalent bonds are strong bonds)

G

A


Completing the Model

•The 2 strands of DNA are “anti-parallel”. They run in opposite directions.

•Place complementary bases paired next to the 1st chain you made. Do NOT tape the chains (base pairs) together. Hydrogen bonds are weak.

•Tape the sugar-to-phosphate along the 2nd chain just like the first.


Structure of DNA


How is DNA packaged?

In eukaryotic cells, DNA is packaged as chromosomes in the nucleus.

In prokaryotic cells, DNA is loose in the cytoplasm – there are no histones or chromosomes.

There is around 2 m of DNA in a cell, so to fit it needs to be tightly coiled and folded.

Eukaryotic DNA is associated with proteins called histones. Together, these form chromatin – the substance from which chromosomes are made.


Structure of eukaryotic chromosomes

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1 of 7© Boardworks Ltd 2009. 2 of 7© Boardworks Ltd 2009 Warm Up: What are the four classes of macromolecules? Which class of macromolecules did we just