B6 - Inheritance, Variation and Evolution Flashcards
DNA - definition
> DNA stands for deoxyribonucleic acid.
It’s the chemical that all of the genetic material in a cell is made up from.
DNA is a polymer.
DNA
> It contains coded information - basically all the instructions to put an organism together and make it work.
So it’s what’s in your DNA that determines what inherited characteristics you have.
DNA is found in the nucleus of plant and animal cells, in really long structures called chromosomes.
Chromosomes normally come in pairs.
DNA is a polymer. It’s made up of two strands coiled together in the shape of a double hellix.
Chromosomes - definition
> Chromosomes are really long strands/molecules of DNA.
Gene - definition
> A gene is a small section of DNA found on a chromosome.
Genes
> Each gene codes for a particular sequence of amino acids which are put together to make a specific protein.
Only 20 amino acids are used, but they make up thousands of different proteins.
Genes simply tell cells in what order to put the amino acids together.
DNA also determines what proteins the cell produces, e.g., haemoglobin, keratin.
That in turn determines what type of cell it is, e.g. red blood cell, skin cell.
Genome - definition
> The term for the entire set of genetic material in an organism.
Genome
> Scientists have worked out the complete human genome.
>Understanding the human genome is a really important tool for science and medicine for many reasons.
Why is the human genome important for science and medicine?
- It allows scientists to identify genes in the genome that are linked to different types of disease.
- Knowing which genes are linked to inherited diseases could help us to understand them and could help us to develop effective treatments for them.
- Scientists can look at genomes to trace the migration of certain populations of people around the world. All modern humans descended from a common ancestor who lived in Africa, but humans can be found all over the planet. The human genome is mostly identical in all individuals, but as different populations of people migrated away from Africa, they gradually developed tiny differences in their genomes. By investigating these differences, scientists can work out when new populations split off in a different direction and what route they took.
What is DNA made up of?
Nucleotides
The structure of DNA
> DNA strands are polymers made up of lots of repeating units called nucleotides.
Each nucleotide consists of one sugar molecule, one phosphate molecule and one ‘base’.
The sugar and phosphate molecules in the nucleotides form a ‘backbone’ to the DNA strands. The sugar and phosphate molecules alternate. One of four different bases - A, T, C or G - joins to each sugar.
Each base links to a base with the opposite strands in the helix.
A always pairs up with T and C always pairs up with G. This is called complementary base pairing.
It’s the order of bases in a gene that decides the order of amino acids in a protein.
Each amino acid is coded for by a sequence of 3 bases in the gene.
The amino acids are joined together to make various proteins, depending on the order of the gen’s bases.
There are parts of DNA that don’t code for proteins. Some of these non-coding parts switch genes on and off, so they control whether or not a gene is expressed.(used to make a protein)
What are nucleotides made up of?
> Each nucleotide consists of one sugar molecule, one phosphate molecule and one ‘base’.
The sugar and phosphate molecules in the nucleotides form a ‘backbone’ to the DNA strands. The sugar and phosphate molecules alternate. One of four different bases - A, T, C or G - joins to each sugar.
Complementary base pairing
> Each base links to a base with the opposite strands in the helix.
A always pairs up with T and C always pairs up with G. This is called complementary base pairing.
What does the order of bases in a gene decide?
> It’s the order of bases in a gene that decides the order of amino acids in a protein.
Each amino acid is coded for by a sequence of 3 bases in the gene.
The amino acids are joined together to make various proteins, depending on the order of the gen’s bases.
There are parts of DNA that don’t code for proteins. Some of these non-coding parts switch genes on and off, so they control whether or not a gene is expressed.(used to make a protein).
Proteins - where are they made?
> Proteins are made in the cell cytoplasm on tiny structures called ribosomes.
Proteins - How are they made?
> To make proteins, ribosomes use the code in DNA.
DNA is found in the cell nucleus and can’t move out of it because it’s really big. So the cell needs to get the code from the DNA to the ribosome.
This is done using a molecule called mRNA - which is made by copying the code from DNA.
The mRNA acts as a messenger between the DNA and the ribosome - it carries the code between the two.
The correct amino acids are brouht to the ribosomes in the correct order by carrier molecules.
types of proteins
> When a chain of amino acids has been assembled, it folds into a unique shape which allows the protein to perform the task it’s meant to do. Here are a few examples of types of protein:
- Enzymes.
- Hormones.
- Structural Proteins.
types of proteins - enzymes
> Act as biological catalysts to speed up chemical reactions in the body.
types of proteins - hormones
> Used to carry messages around the body.
>E.g. insulin is a hormone released into the blood by the pancreas to regulate the blood sugar level.
types of proteins - structural proteins
> Are physically strong.
>E.g. collagen is a structural protein that strengthens connective tissues (like ligaments and cartilage).
Mutations -definition
> Occasionally, a gene can mutate.
A random change in an organism’s DNA.
They can sometimes be inherited.
Mutations
> Mutations occur continuously. They can occur spontaneously, e.g. when a chromosome isn’t quite replicated properly.
However, the chance of mutation is increased by exposure to certain substances or some types of radiation.
what do mutations change?
> Mutations change the sequence of the DNA bases in a gene, which produces a genetic variant.
As the sequence of DNA bases codes for the sequence of amino acids that make up a protein, mutations to a gene sometimes lead to changes in the protein that it codes for.
Effect of mutations
> Most mutations have very little or no effect on the protein. Some will change it to such a small extent that its function or appearance is unaffected.
However, some mutations can seriously affect a protein.
Sometimes, the mutation will code for an altered protein with a change in its shape. This could affects its ability to perform its function. E.g.:
1. If the shape of an enzyme’s active site is changed, its substrate may no longer be able to bind to it.
2. Structural proteins like collagen could lose their strength if their shape is changed, making them pretty useless at providing structure and support.
If here’s a mutation in the non-coding DNA, it can alter how genes are expressed.
Types of mutation
- Insertions.
- Deletions.
- Substitutions.