DP Biology Unit 1: Life under the microscope - HL

Goldilocks zone

The range of orbital distances around a star in which liquid water may exist on a planet or natural satellite. Also known as the habitable zone

asteroids

Astronomical objects that orbit stars that are composed of rock, metal ores and, in the case of comets, ice

Hypothetical types of biochemistry

Forms of biochemistry agreed to be scientifically viable but not proven to exist at this time

atmosphere

A layer of gases that surrounds the Earth and has many vital functions, including protecting the Earth from harmful solar radiation and regulating the Earth's temperature

inorganic molecules

Molecules that do not contain carbon and hydrogen. Inorganic molecules are typically found in non-living things

organic molecules

Molecules that contain carbon and hydrogen. Most biological molecules, including proteins, carbohydrates, lipids and nucleic acids are organic molecules

reducing gases

Gases that can donate electrons to other molecules, reducing other molecules while themselves becoming oxidised

spontaneous origin of cells

Catalysis, self-replication of molecules, self-assembly and the emergence of compartmentalization were necessary requirements for the evolution of the first cells (not to be confused with 'spontaneous generation')

catalysis

The acceleration of a chemical reaction by a catalyst

catalyst

A substance that increases the rate of a reaction and is not used up. Although it speeds up a reaction, the catalyst itself is not changed by the reaction

falsification (NOS)

Scientists can use evidence to falsify a claim formulated as a hypothesis, theory or model, but they cannot prove with certainty that such a claim is true. There is therefore inherent uncertainty in all scientific knowledge. Nonetheless, many theories in science are corroborated by strong evidence and allow for prediction and explanation. Scientists must remain open-minded with respect to new evidence

hypotheses (NOS)

Scientists make provisional explanations for the patterns that they have observed in natural phenomena. These hypotheses can be tested, with further observations or experiments, to obtain support for a hypothesis or show that it is false

theories (NOS)

Scientists develop general explanations that are widely applicable, based on observed patterns or tested hypotheses. Predictions can be generated from these theories by deductive reasoning. If these predictions are tested, they may corroborate a theory or show that it is false and should be rejected. Paradigm shifts take place when a new theory replaces an old one. The term "law" is sometimes used for statements that allow predictions to be made about natural phenomena without explaining them

models (NOS)

Scientists construct models as artificial representations of natural phenomena. They are useful when direct observation or experimentation is difficult. Models are simplifications of complex systems and can be physical representations, abstract diagrams, mathematical equations or algorithms. All models have limitations that need to be considered in their application

protocells

Simple, self-organised and potentially primitive cell-like structures that are believed to have preceded the first true cells on Earth

pre-biotic

The period in time before life existed on Earth

Miller and Urey experiment

a 1952 investigation still at the core of most origins of life theories today because it showed that organic compounds can be formed from inorganic precursor molecules

coalescence

the process by which two or more droplets, bubbles, or particles merge during contact to form a single daughter droplet, bubble, or particle

bilayer

A double layer of lipid molecules

ribozymes

RNA molecules capable of acting as catalysts and increasing the rate of chemical reactions

messenger RNA (mRNA)

A type of RNA that carries the genetic information from DNA in the nucleus to ribosomes in the cytoplasm, where it is used as a template to synthesise proteins

ribosomal RNA (rRNA)

A type of RNA molecule that is a structural component of ribosomes, the cellular organelles responsible for protein synthesis

transfer RNA (tRNA)

A type of RNA molecule that acts as an adaptor during translation, bringing amino acids to the ribosome and aligning them in the correct order based on the mRNA sequence

endosymbiosis

A theory that eukaryotic cells evolved by engulfing and incorporating prokaryotic cells, which then became organelles within the eukaryotic cell

cyanobacteria

A group of photosynthetic bacteria that obtain energy through photosynthesis. They are also commonly known as blue-green algae, although they are not true algae

naked DNA

DNA that is not associated with histone proteins. Because it is not associated with protective molecules, naked DNA is more prone to damage and errors during replication

cell aggregation

The process by which cells come together to form a group or a cluster

epigenetics

The study of how your behaviors and environment can cause changes that affect the way genes are expressed

cristae

Folds of the inner membrane of mitochondria, increasing the surface area for cellular respiration

matrix

Enclosed region of the inner membrane of mitochondria containing enzymes and products for Krebs cycle

intermembrane space

Small space between the inner membrane and outer membrane of mitochondria

Krebs cycle

The series of chemical reactions that occur in the mitochondrion and produce ATP

stroma

Space between the inner membrane and thylakoid membranes in chloroplasts containing enzymes and products for the Calvin cycle

thylakoids

Flattened, membrane-bound sacs in chloroplasts that contain the photosynthetic pigments and proteins necessary for the light-dependent reactions of photosynthesis

thylakoid membranes

Membranes forming thylakoids in chloroplasts for light-dependent reactions in photosynthesis

thylakoid space

The interior region of a thylakoid in chloroplasts, where the light-dependent reactions of photosynthesis occur

granum/grana

Stack of thylakoid membranes in plant chloroplasts that contain chlorophyll

lamellae

Structures that join granum

Calvin cycle

A series of biochemical reactions that occur in the stroma of chloroplasts during the light-independent reactions of photosynthesis. The Calvin cycle involves the fixation of carbon dioxide, reduction of carbon compounds and regeneration of RuBP, leading to the production of carbohydrates

nuclear pores

A complex structure that forms a channel through the nuclear membrane (double membrane surrounding the nucleus in eukaryotic cells) to regulate the transport of materials in and out of the nucleus

chromosomes

A long molecule of DNA containing part of the genetic material of an organism

cell division

The process by which a 'parent' cell undergoes division to create 'daughter' cells by one of several pathways; mitosis, binary fission, budding or in the case of gamete formation, meiosis

mitosis

Equational cell division resulting in daughter cells that are genetically identical to the parent cell

meiosis

Cell division that produces gametes and reduces the amount of genetic information in each cell

bound ribosomes

Ribosomes attached to cytosolic side of the endoplasmic reticulum, the proteins that it produces end up inside the lumen of the RER and then exported for use outside of the cell. As most cells in organisms produce proteins for use in the body, these tend to be more numerous in the cell than free ribosomes

free ribosomes

Ribosomes located in the cytoplasm that make proteins that remain inside the cell's cytoplasm and used inside the cell

cytosolic

Cytosolic (also called cytoplasmic) refers to the part of the cell that is contained within the plasma membrane but outside of the organelles

ER signal sequence

A short sequence on a protein that directs the protein towards the endoplasmic reticulum. When joined with a ribosome, it directs the ribosome towards the ER membrane. Proteins for use inside the cell do not have this sequence in their mRNA

cis, medial, and trans compartments

Three compartments in the Golgi apparatus involved in sorting and modifying proteins

exocytosis

A type of transport in which a cell releases materials into its exterior by fusing vesicles containing these molecules with the cell membrane

endocytosis

A process by which cells take in molecules and particles from their environment by engulfing them into vesicles formed by the plasma membrane

transport vesicles

Transport materials from one part of the cell to another. An example is the transport of proteins from the rough endoplasmic reticulum to the Golgi apparatus

secretory vesicles

Store and transport molecules to be secreted outside the cell, such as hormones, neurotransmitters and digestive enzymes

lysosomes

Contain hydrolytic enzymes that can break down macromolecules such as proteins, carbohydrates and lipids. They play a key role in the degradation of cellular waste products and in removing damaged or aged organelles

peroxisomes

Similar to lysosomes but have a different set of enzymes that are involved in the detoxification of harmful compounds and lipid metabolism

clathrin

Protein involved in forming vesicles in a wide range of cellular processes, including: endocytosis, phagocytosis, the transport of cargo from the Golgi apparatus to the plasma membrane and the formation of lysosomes

invaginate

The process of folding or inward protrusion of a structure, such as the inward folding of the cell membrane to form a vesicle during endocytosis

virus

Range in size from 20 nm to 500 nm. Usually considered to be infectious, pathogenic agents, they are also powerful agents in evolutionary mechanisms (about 8% of your DNA will be viral) and aslo have the potential to be used as tools for treating diseases, such as in gene therapy, cancer treatment and the development of vaccines

virions

The basic unit of a virus outside of a host cell

capsid

The protein shell of a virus that surrounds and protects the genetic material

genome

The total of all genetic information of an organism

viral genomes

Some viruses contain as little as four genes, and others have many more - a recently discovered 'giant' virus is estimated to contain 2500 genes. They can be single or double stranded RNA or single or double stranded DNA

host cell

The cell that is infected (by the virus)

(viral) envelope

A membrane that surrounds the capsid, and is made of lipids and proteins, acquired from the host cell membrane when it is released

bacteriophage lambda

A type of phage virus that infects Escherichia coli bacteria

obligate intracellular parasites

A living organism (or virus) that lives in or on a living thing, benefiting from the pairing at the expense of the host

receptor-mediated fusion

The process by which a virus binds to a receptor on a host cell membrane to fuse with the host cell membrane and enter the cell

lytic cycle

A viral reproductive cycle involving rapid production of viral progeny which lyse and destroy the host cell

lysogenic cycle

A viral reproductive cycle involving integration of the virus genome into the host cell genome

lyse

Breaking something apart into smaller pieces

viroids

An infectious entity affecting plants, smaller than a virus and consisting only of nucleic acid without a protein coat

transposons

Sequences of nucleic acid (DNA or RNA) that are able to move position within the genome

universal (genetic code)

All living organisms contain the same four DNA bases: adenine, thymine, cytosine and guanine, and use the same cellular machinery to utilise the instructions in the genetic code to produce protein

convergent evolution

Pattern of evolution where distantly related organisms evolve similar traits in response to environmental similarities

retroviruses

A virus that has RNA rather than DNA as its genetic material

reverse transcriptase enzymes

Enzymes that allows a virus to use RNA to synthesise DNA

RNA polymerases

Enzymes that use a DNA template to synthesise RNA

mutation

A change in the sequence of genetic material

recombination

The rearrangement of genetic material

horizontal gene transfer

The exchange of genetic material between individuals that does not involve reproduction

Human Immunodeficiency Virus (HIV)

A retrovirus first identified in the early 1980s, transmitted through infected body fluids and primarily infects CD4+ cells of the immune system, leading to the disease Acquired Immunodeficiency Syndrome (AIDS)

influenza 'flu'

An RNA virus (and therfore less accurate means of replicating its genetic material than DNA viruses or living organisms) with high mutation rates in surface proteins that make it more difficult for the host immune system to identify and protect against the virus, and is also a contributing factor to why flu vaccines tend to have a relatively low effectiveness compared with other vaccinations

vaccines

A biological preparation that provides immunity to a particular disease by stimulating an immune response

SARS-CoV-2

An RNA virus responsible for causing the infectious disease COVID-19, more prone to mutations than DNA viruses. Its high replication and mutation rate resulted in variants such as Delta and Omicron and is why it continues to pose a threat to public health

proteome

Entire set of proteins within a cell or organism