Molecules of Life

Part 1

Learning Objectives

• Explain that the mitochondria is the site of respiration.

• Describe how Watson & Crick built a model of DNA.

• Explain how genes and ribosomes are involved in making proteins.

Success Criteria

• You can label a diagram of an animal cell with its main components.

• You can create a leaflet on the discovery of DNA.

• You can answer some questions on protein synthesis.

StarterUse a whiteboard and marker to write down ideas you already have about:• DNA• Genes• Chromosomes• Inheritance

You have 5 minutes until you feedback to the rest of the class.

What’s in a Cell?

• An animal cell contains the following parts:

• Copy this diagram into your book.

Cell membrane – controls the

movement of substances in and

out of the cell.

Nucleus – carries genetic information.

Cytoplasm – where many chemical

reactions happen.

Chromosomes – genetic information is carried on these structures (DNA).

Mitochondria

• Along with everything present on the previous slide, there are also structures called mitochondria.

• Add a couple to your diagram.

• Remember back to year 10: You were taught that aerobic respiration released energy from glucose.

• The mitochondria are the site of this reaction.

Mitochondria – the site of aerobic respiration.

Task

1. Match up each part of the cell with the job it does. Copy the completed table into your book.

2. Suggest a reason why sperm cells have many mitochondria.

3. Why might a cell need to make proteins?

Part of Cell JobNucleus Makes up most of the cell and is where

dissolved chemicals can react.Cytoplasm Structures in which respiration takes place.

More active cells will have a larger amount.Cell membrane Large structure which contains the

chromosomes and therefore, the genetic material of the cell.

Mitochondria The barrier around the cell that controls the entry and exit of substances.

From DNA to Chromosomes

• It’s easy to forget DNA, genes and chromosomes mixed up.

• DNA is a molecule that is twisted into a double helix shape – like this.

• The molecule is very long and is split into genes which are codes for making proteins.

• A chromosome is simply a very long DNA molecule that has been folded into a shape like this:

hair

colo

ur g

ene

There’s a lot more DNA packed into

the chromosomes than shown here!

Task

1. Complete Worksheet 1 and then stick it in your book.

Answers:A. Top to bottom: membrane, nucleus, cytoplasm, chromosome, DNA, gene.B. Because liver cells need more energy from respiration.

Watson & Crick

• Watson & Crick contributed a lot to discovering the structure of DNA.

• However, there were others involved in the discovery too – namely Rosalind Franklin.

• She was instrumental, as it was her X-ray crystallography technique that indicated DNA had a double helix shape.

• Another scientist, Erwin Chargaff was responsible for discovering that DNA contained 4 bases (next lesson).

HIGHER

Higher

• The code stored within a DNA molecule is essential for making proteins.

• Proteins are made of chains of amino acids and the DNA controls the order of amino acids in a protein.

• Eg:

• This protein synthesis is carried out by ribosomes.

Gene 1:Code = ATC GCT TGA CGT ACT

AminoAcids:

Gene 2:Code = GCT GCT ATC CGT TAC

AminoAcids:

Task

ALL:Create a leaflet on the discovery of DNA using information from this lesson and the student textbook.Include ideas about:• the structure of DNA• the names of the two scientists who first built a model of DNA• the X-ray data they used to help them and the scientists that produced

the X-rays• the name of the scientist who found that there were pairs of bases• the scientists that gained the Nobel prize for their work

HIGHER:Your leaflet should also include• reasons why some people may not have believed the scientists who

made the discovery• reasons why we are now more certain about the structure of DNA• how DNA is linked to the role of ribosomes in the cell

HIGHER EXTENSION TASK

Higher Extension Task

Read page 11 of the new student textbook and answer the following questions:

1. Which evidence was used to show DNA was a double helix?

2. Suggest why ribosomes can’t be seen using a light microscope.

3. Why was Rosalind Franklin’s work so important in the discovery of DNA?

4. Why is it important that scientists repeat the work of other scientists.

5. As DNA is made of two strands, can you think of a possible copying mechanism it may have?

Answers

1. The X-ray crystallography evidence obtained by Rosalind Franklin and Maurice Wilkins.

2. Light microscopes aren’t powerful enough.3. It showed that DNA wasn’t a triple-stranded molecule,

but a double-stranded molecule.4. To validate the results of others.5. The strands separate and form a template for new

strands to form.

PLENARY

Answer the questions 1-10 in the student textbook.

Answers

Q1 Nucleus • Q2 Gene • Q3 Watson and Crick • Q4 Muscle cells need a lot of energy and mitochondria release energy during respiration Q5 Bases • Q6 X-ray crystallography • Q7 Erwin Chargaff • Q8 Too small • Q9 Confirmed DNA was a double helix not a triple helix • Q10 To make the results more valid

Learning Objectives

• Explain that the mitochondria is the site of respiration.

• Describe how Watson & Crick built a model of DNA.

• Explain how genes and ribosomes are involved in making proteins.

Success Criteria