Topic 4 🔑 definitions

What’s a gene

What’s a gene

A gene is a sequence of DNA bases that codes for either a polypeptide or a functional RNA.

What’s functional RNA

Genes that don’t code for a polypeptide code for fRNA

Functional RNA is RNA other than mRNA which perform special tasks during protein synthesis.

Like tRNA or rRNA

Genome

Complete set of genes in a cell

Proteome

Full range of proteins that the cell is able to produce

What are introns

introns are found in genes that do code for polypeptides. introns are the sections that don’t code for amino acids in these genes.

Removed during protein synthesis

Prokaryotes don’t have introns.

Exons

Sections of a gene that do code for amino acids.

Allele

Different forms of the same gene.

In a homologous pair alleles coding for the same characteristic e.g eye colour have the same locus (location).

Protein synthesis

Transcription - where DNA is copied into a molecule called mRNA

Translation- where mRNA joins with an organelle called a ribosome. The code is used to synthesise a protein.

What’s mRNA

Made during transcription and carried the genetic code from the DNA in the nucleus to the ribosomes.

It’s a single polynucleotide strand.

Groups of 3 bases are called codons

What’s tRNA

Involved in translation. It carries the aminos to the ribosomes to make a protein.

Single polynucleotide strand folded into a clover ☘ shape. Hydrogen bonds between bases hold this shape.

Every tRNA molecule has a specific 3 bases at one end called an anticodon 🐜 and an amino acid binding site at the other end.

The genetic code is

Non overlapping - each triplet is read in sequence

Degenerate- there are more possible combinations of triplets then there are amino acids, 20 amino acid 64 possible triplets. This means that an amino can be coded for by more than one specific triplet. E.g UAU and UAC both make tyrosine. Also some triplets don’t code, they’re stop signals like UAG.

Universal- the same specific base triplets code for the same animo in all living organisms. E.g UAU codes for tyrosine in all animals.

What is genetic diversity?

Genetic diversity is the number of different alleles of genes in a species or population.

What is natural selection

When an allele that codes for a characteristic that increases the chance of an organism surviving, its frequency in the population increases.

What’s directional selection?

Where individuals with alleles for extreme characteristics are more likely to survive and reproduce.

This could be in response to an environmental change.

Stabilising selection

Where individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce.

Occurs when the environment isn’t changing and reduces the range of possible characteristics.

What’s phylogeny ?

Phylogeny is the study of evolutionary history of groups of organisms.

What’s phylogenic classification?

Phylogenic classification is arranging species into groups (taxa) based on evolutionary origins. Uses a hierarchy in which smaller groups are placed in larger groups with no overlap.

What’s taxonomy ?

The science of classification. Involves naming organisms and organising them.

There are 8 levels these groups are called taxa. Each is a taxon.

What’s biodiversity ?

The variety of living organisms in an area 🪼🐠🐟🐙🪸🐚

It ranges from local biodiversity e.g in your back garden to global biodiversity 8.7 mil species

Habitat

The place where an organism lives e.g sea or a field

Community

All the populations of different species in a habitat.

Biodiversity can be measured using

Species richness - is a just the number of different species in a community. You take random samples of a community and count.

Index of diversity - describes the relationship between the number of species in a community and the number of individuals in each species (abundance). Higher number more diverse