B3a: Molecules of life

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Cells

This is a diagram of an animal cell. There are labelled cell structures that make animal cells unique:

This is a diagram of a plant cell. It has all the structures of an animal cells (ie. ribosome and mitochondria) and a few extra:

This is a diagram of a bacterial cell. It is much simpler and smaller than plant and animal cells.

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Mitochondria and ribosomes

What are mitochondria?

Mitochondria are tiny structures found in cells (one is called a mitochondrion).

What happens in the mitochondria?

Respiration,

the chemical reaction that releases energy from glucose, happens in

mitochondria. This provides energy for life process such as movement and

growth.

Why do liver and muscle cells have larger numbers of mitochondria?

Active cells, such as liver and muscle cells, has to have a higher respiration rate. This is so that they have more energy to function as they are constantly used.

What are ribosomes?

They are found in the cytoplasm and are the site of protein synthesis.

Why can't we see them?

Ribosomes are too small to be seen with the light microscope. They can only be seen using an electron microscope.

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Watson and Crick

Scientists struggled for decades trying to work out the structure of DNA.

Francis Crick and James Watson were the first scientists to build a model of the DNA in 1953.

They used data from other scientists to help them understand the structure. This included:

X-ray data, from Maurice Wilkins and Rosalind Franklin, showing that DNA is a double helix.

Other data showing that bases occurred in pairs.

They were awarded The Nobel Prize in Physiology or Medicine 1962. They were awarded 9 years later as new discoveries such as Watson and Crick's aren't widely accepted and other scientist had to repeat the work to make sure the results are reliable.

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DNA

What is DNA?

DNA controls the production of different proteins. These are needed for the growth and repair of cells.

Gene

Section of a DNA

Each gene is a container of a different sequence of bases coding for a particular protein - genetic code

Chromosomes

Contained in the cell's nucleus

Long, coiled molecules of DNA

Divided up into regions called genes.

DNA Helix

Double strands of nucleotides (bases) coiled to form double helix

Cross-link between the two strands, formed by pairs of bases

Base pair

A, T

C, G

These are called complimentary base pairs

Backbone

Bases are attached to this

Sugar phosphate structure

How does DNA replicate itself?

DNA copies itself every time a cell divides - so each new cell has a full amount of DNA.

To copy itself, the DNA double helix 'unzips' - to form 2 single strands.

New nucleotides (floating freely in nucleus) the join on using complimentary base-pairing - making an exact copy of the DNA on the other strand.

The results is 2 double stranded molecules of DNA that are identical to the original molecule of DNA.

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Protein Synthesis

How are proteins made?

Complementary base pairs form a code

They are 'read' in groups of 3s - this is known as base triplet

Each triplet specifies a particular amino acid

As DNA always stays in the nucleus, proteins are assembled at the ribosomes

So another molecule - mRNA - carries a copy of the coded instructions, in a gene, out of the nucleus

The sequence of amino acids in protein will govern how protein will fold

Each different type of protein has a specific shape

What is mRNA?

Messenger RNA (mRNA) is a single stranded molecule - a copy of one strand of DNA

mRNA from DNA is called transcription

Proteins from mRNA is called translation