Cambridge Pre-U Biology - 1.6 Genes and Protein Synthesis PART 1 Sample

MAKING SENSE OF
Icons CC – The Pink Group
Copyright©2017HenryExham

Copyright © 2017 Henry Exham
• This is it! This is how the whole thing works!
• You now have enough biology knowledge to understand how
all the pieces of the puzzle go together to build living
organisms.
• In this topic you will learn how the genetic code works to
make polypeptides and RNA which go onto give cells their
structure and function and therefore build organisms.
• You will learn the details of exactly how this works and how
these instructions are inherited by the next generation.
• Finally you will learn about what can go wrong!
2

MAKING SENSE OFMAKING SENSE OF
Gene expression
Variation
Inheritance
3
Mutations
The genetic code and protein synthesis
PART1PART2

a) Define a gene as a unit of inheritance or as an ordered sequence of
nucleotides located at a particular locus on a particular chromosome,
which codes for a particular protein or, in certain cases, a functional or
structural RNA molecule and discuss the limitations of these definitions
with reference to introns, exons and promoters.
b) Describe the genetic code and discuss the extent to which it is true that
the code is universal to all organisms.
c) Explain protein synthesis in terms of transcription and translation,
including the roles of DNA, mRNA, tRNA and ribosomes.
d) Describe, in outline, eukaryotic introns, exons and the splicing of mRNA.
4

• By now you should know what DNA looks like and
how it divides but we still haven't covered how it
actually works!
5

• The sequence of bases in DNA is actually a code to
make proteins.
• We have already explained how important proteins
are to living organisms.
• Machinery in cells can read this code and
manufacture the proteins (protein synthesis).
• Every three bases on the DNA codes for an amino
acid.
• This is called the triplet code.
6

• There are 64 combinations of bases (43) for only 20
amino acids, so amino acids are usually coded for by
more than one triplet code.
• For example the codes TGA, TGG, TGT and TGC all code
for the amino acid threonine.
• This is known as a degenerate code, but its good because
it means that often mutations in the DNA don’t actually
change the eventual protein produced so it protects the
organism.
• Most of your DNA actually doesn't’t code for proteins but
it regulates when and where to make them.
7

• The triplet code works the
same in all living organisms
(with a couple of exceptions).
• Therefore it’s (almost)
universal.
• That means we can swap DNA
between organisms!
• This is explained later in the
course.
8

• As mentioned there are a couple of exceptions to the
genetic code being universal.
• The majority of these exceptions are found in the DNA
inside the mitochondria (mtDNA) which code for different
amino acids than the nuclear DNA.
9By Jfitz1974 - Using Adobe Photoshop Elements, CC BY-SA 3.0, https://en.wikipedia.org/w/index.php?curid=41045504
Recently some modifications have
also been discovered in the nuclear
DNA of some species.

10
So what
exactly is a
gene?

• You probably know this definition:
11
A gene is a section of DNA that
codes for a particular protein.
However, at this level we can
go into this definition further
and actually see why this is
not a good definition at all.

12
By OpenStax College - Anatomy & Physiology, Connexions Web site. http://cnx.org/content/col11496/1.6/, Jun 19, 2013., CC
BY 3.0, https://commons.wikimedia.org/w/index.php?curid=30148169
But what about proteins
with quaternary structure
like this one? Are they
coded for by one gene?

13
By OpenStax College - Anatomy & Physiology, Connexions Web site. http://cnx.org/content/col11496/1.6/, Jun 19, 2013., CC
BY 3.0, https://commons.wikimedia.org/w/index.php?curid=30148169
No they are not, they are made of
multiple polypeptides coded for by
separate genes and then modified by
the Golgi apparatus.
A gene is a section of DNA that codes
for a particular polypeptide.
Therefore . . .

• But in actual fact genes
don’t always code for
polypeptides, they can
also code in certain
cases for a functional
or structural RNA
molecule.
14
A gene is a section of DNA that codes
for a particular polypeptide.
By Yikrazuul - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=10242870
Large ribosomal subunit (50S) of Haloarcula marismortui.
The ribosomal proteins are shown in blue, the rRNA in
ochre.

• Another problem with this definition is that it is not
one discrete section of DNA that makes up the actual
gene. Its more complicated than that!
• A better definition of a gene’s structure is to say an
ordered sequence of nucleotides located at a
particular locus (plural loci) on a particular
chromosome.
15
A gene is a section of DNA that codes for a particular
polypeptide or in some cases an RNA molecule.

• But genes are not all at one locus! They are actually
interrupted by non-coding sequences called introns. And
begin with sections called promoters.
• The coding sequences in the gene are called exons.
16
A gene is a section of DNA that codes for a particular
polypeptide or in some cases an RNA molecule.

To download the whole
presentation visit
www.MrExham.com

This PowerPoint is protected under copyright.
It is designed for educational use. Either personal study or to be
presented to a class. It may be edited or duplicated for these purposes
only.
It must not be shared or distributed online in any format.
Some images used are under a separate creative commons license, these
are clearly marked.
Brought to you by MrExham.com

Cambridge Pre-U Biology - 1.6 Genes and Protein Synthesis PART 1 Sample

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Cambridge Pre-U Biology - 1.6 Genes and Protein Synthesis PART 1 Sample

Similar to Cambridge Pre-U Biology - 1.6 Genes and Protein Synthesis PART 1 Sample (20)

More from mrexham

More from mrexham (20)

Recently uploaded

Recently uploaded (20)

Cambridge Pre-U Biology - 1.6 Genes and Protein Synthesis PART 1 Sample