As Biology Dna And Genetic Diversity

Front 1

Describe DNA in Prokaryotic Cells

Back 1

Short, Circular and not associated with any proteins, do not form chromosomes.

Front 2

Describe DNA in Eukaryotes

Back 2

DNA is found in the nuclei and is very long, linear and associated with proteins called Histones

Front 3

Where else might DNA be found in a cell?

Back 3

The Mitochondria and Chloroplasts have their own DNA which codes for their enzymes.

It is similar to Prokaryotic DNA. (Short, Circular, not associated with proteins)

Front 4

What are genes and what do they code for?

Back 4

They are sequences of bases and they code for The Amino Acid Sequence of Polypeptides or Functional RNA e.g tRNA and Ribosomal RNA

Front 5

What are alleles?

Back 5

Alleles are different forms of the same gene which occupy the same relative position (Locus) and code for different types of the same characteristic

Front 6

What is meant by the genetic code being Universal, Degenerate and Non-Overlapping?

Back 6

The code is universal because the same base triplets code for the same amino acids in all organisms with very few exceptions.

It is degenerate because the same amino acids are coded for by multiple different triplets or codons.

None-Overlapping because triplets are read separately in groups of three, no overlap.

Front 7

What is a Genome and a Proteome?

Back 7

Genome is the complete set of genes in a cell

Proteome is the full range of proteins that a cell is able to produce

Front 8

How do different alleles arise?

Back 8

Mutations occur in a gene and change the base sequence, making a new allele.

This changes the Amino Acid sequence in the Polypeptide produced.

This will change the tertiary structure of the protein by changing position of Hydrogen and Ionic bonds.

Usually this will make it non-functional as the new shape is not right (eg for enzymes) but sometimes the new allele can be beneficial or just as functional and so be passed on,

Front 9

What are the Non-Coding sections of DNA?

What are the Coding sections called?

Back 9

Multiple Repeats: Non-coding base sequences between genes

Introns: Base sequences within genes which do not code for any amino acid sequences. They are removed in RNA translation and separate the Exons which do code for Amino Acid Sequences

Front 10

What is the structure of Messenger RNA (mRNA)

Back 10

It has a single stranded linear structure, arranged in a single helix. It is long, thousands of mononucleotides.

Base sequence determined by the DNA base sequence it is transcribed from.

It has Codons (mRNA base triplets) which correspond to Amino Acids and determine the sequence in the polypeptide formed

Front 11

What is the structure of Transfer RNA (tRNA)

Back 11

Relatively small molecule, up to around 80 nucleotides. Single stranded but folded.

Has a clover leaf shape due to hydrogen bonds between complimentary bases.

Has an Anticodon at one end which lines up next to codons on mRNA during Translation.

At the other end has Amino Acid Binding Site.

there are enough different types of tRNA to cover all the possible codons and amino acids.

Front 12

What is Transcription?

Back 12

The process which produces mRNA from DNA

Front 13

Outline the Process of Transcription

Back 13

1. The relevant section of DNA molecule uncoils and the two strands are separated by DNA Helicase which breaks the hydrogen bonds (enzyme acts on specific region which is needed to separate is)

2. The exposed bases on one of the DNA strands act as template and RNA nucleotides line up due to complimentary base pairing, so have same sequence

3. Individual RNA nucleotides are then joined together with phosphodiester bonds by the enzyme RNA polymerase. The DNA strands rejoin behind the newly forming mRNA so only about 12 bases exposed at a time

4.When RNA Polymerase reaches a stop code triplet, it detaches and so does the pre-mRNA.

5. This pre-mRNA then leaves the nucleus through nuclear pores.

6. It then undergoes splicing

Front 14

What is splicing of pre-mRNA ?

Back 14

In Eukaryotic cells, DNA in a gene has Exons which code for proteins and Introns which are non-coding.

Before mRNA forms, the pre-mRNA has to have the introns removed and then the Exons joined together. This is splicing.

Once splicing is done, the mRNA is small enough to pass through nuclear pores.

Most Prokaryotes do not have introns so do not require splicing. Transcription results directly in mRNA production in prokaryotes.

Front 15

What happens during Translation?

Back 15

The sequence of Codons on an mRNA strand is used to determine the sequence of Amino Acids in a polypeptide. This is carried out using ribosomes in the cytoplasm and tRNA which bring amino acids.

Front 16

Outline the process of Translation

Back 16

mRNA attaches to a ribosome by its Start codon. Multiple ribosomes can attach at the same time to form polypeptides.

A tRNA with a complimentary anticodon to the first Codon moves in to the ribosome and brings its specific amino acid.

Two tRNA molecules do this at the same time.

The amino acids the amino acid of the second tRNA joins to the amino acid of the first tRNA in a condensation reaction which requires energy from hydrolysis of ATP.

The first tRNA moves away and collects another amino acid from the cytoplasm.

More tRNA molecules join in the order determined by the codons on the mRNA, repeating the same process of joining and then leaving their amino acid behind.

Once the ribosome reaches the Stop Codon the polypeptide detaches and folds into a secondary and tertiary structure.

Front 17

What can cause genetic diversity within a species?

Back 17

• Gene Mutations
• Meiosis
• Random fusion of Gametes during Fertilization
• Chromosome Mutations

Front 18

What things cause mutations in DNA base sequence?

Back 18

Mutagenic Agents e.g Benzene, Ionising radiation, Radon.

Also mutations occur spontaneously during DNA replication.

Front 19

What is a deletion mutation?

Back 19

The removal of one or more bases which happens when nucleotides are left out of DNA replication for some reason.

This results in a frame shift which alters all the triplets from the point of deletion.

This changes every amino acid in the sequence after the point of deletion and usually forms a non-functional protein.

Front 20

What is Substitution Mutation?

Back 20

The replacement of one or more bases with another. A new triplet may code for a different acid.

May result in a non functional protein or may be a functional protein and a new allele of that gene.

Can remain the same due to degeneracy.

Front 21

What is Meiosis and what does it produce?

Back 21

It is a type of cell division which produces gametes, genetically different cells with half the number of chromosomes of the original cell (Haploid Number)

Front 22

Outline the Process of Meiosis

Back 22

During late interphase the DNA is replicated and all cell organelles are replicated with an increase in Protein and ATP synthesis.

During the first meiotic division, the members of each Homologous Pair form a bivalent, lining up side by side. Sometimes crossing over can occur. The Homologous chromosomes then separate into two different cells, one chromosome from each pair going in to each of the cells.

In the Second Meiotic Division, the chromatids of each chromosome move apart to produce 4 cells

Front 23

What is Independent Segregation of Homologous Chromosomes and how does it result in diversity?

Back 23

Meiosis 1, each chomosome lines up alongside it's homologous partner.

When they line up on the cell equator they do so at random and independent from all of the other pairs.

Either chromosome in the homologous pair can go to either pole to form new cells.

This means that the combination of chromosomes received is unique to every gamete and so each receives it's own combination of alleles from the mother and father.

Front 24

What is Genetic Recombination by Crossing Over and how does it result in diversity?

Back 24

When the Homologous Chromosomes line up to form a bivalent in Meiosis 1, the chromatids of each pair become twisted around each other and can break in places.

The broken portions can be replaced by the same portion from the homologous partner, resulting in the exchange of alleles between the two chromatids.

In this way new combinations of alleles are formed which exist on the Chromatids in the final 4 gametes.

Front 25

How can Chromosome Mutations occur and what do they cause to happen?

Back 25

If a homologous pair does not separate in Meiosis 1 due to Non-Disjunction it means that during Meiosis 2 one of the cells will have an additional chromosome and so 2 gametes will have an additional chromosome while 2 will have one less than usual

Front 26

What is the definition of Genetic Diversity?

Back 26

The number of different alleles of genes in a population

Front 27

What are the main principles of Natural Selection?

Back 27

• In a population there will be variations within a gene due to random mutations which result in new alleles of a gene.
• A new allele of a gene may benefit an organism, leading to increased reproductive success.
• A change in the environment leads to organisms with the advantageous allele being selected for by having increased reproductive success as they are better adapted.
• Organisms with advantageous alleles survive and reproduce while those without do not, leading to differential reproductive success.
• Over many generations the frequency of the Advantageous Allele increases as it is inherited by members of the next generation

Front 28

What is Directional Selection?

Back 28

Selection that occurs when there is a change in the environment.

Extreme phenotypes are selected for and the mean changes, though the frequency of the mean does not change.

Front 29

What is Stabilising Selection?

Back 29

Selection that occurs when there is No Change in the Environment

Extreme Phenotypes are Selected Against and the Frequency of the Mean increases while the position of the Mean does not change.