A2.1 - A2.2 Biology

HL IB Biology section A2.1 and A2.2

Eukaryotes

• Belonging to multicellular organisms

• Protista, Fungi, Plants, Animals

• Believed to have evolved from prokaryotic cells

Golgi body

Stores, modifies and packages proteins

Free Ribosomes (E)

Synthesis of proteins for use IN the cell

80S

rER (rough Endoplasmic Reticulum)

Synthesis of proteins for use OUTSIDE of the cell

Lysosomes

Contain digestive enzymes, and can fuse with vesicles containing damaged organelles

Nucleus

Surrounded by a double membrane with pores, contains the cell’s DNA

Mitochondria

The site of Aerobic respiration- the production of ATP energy

Plasma membrane (E)

• Controls the movement of materials into and out of the cell

• Allows cell to maintain concentrations of substances that are very different from those in the surrounding environment

• Semi-permeability replies on the lipid bilayer

Cytoplasm (E)

• Fluid within the plasma membrane where organelles occur

• Mainly composed of water with many substances dissolved or suspended in it

• Enzymes catalyze different chem reactions

Prokaryotes

Belong to single celled organisms

Ex. Bacteria

Cell Wall (peptidoglycan)

A rigid non-cellulose structure that surrounds cells of bacteria or plant cells

Plasma membrane (P)

A phospholipid bilayer that surrounds the cell

Cytoplasm (P)

The gel-like fluid inside the cell membrane where the reactions of metabolism occur

Pili

Hair-like protein structure that allows bacteria to attach to things

Flagella

Long, thin, whip-like structures, made from the protein ‘flagellin’ that enables movement

Ribosomes (P)

Organelles made of protein and RNA that direct protein synthesis

70S

Nucleoid

A dense region of DNA in a prokaryotic cell

Conditions of early earth

• Pre-biotic period (no life)

• Lack of O2 = lack of ozone

  (due to O reacting with other elements)

• Higher concentration of methane

  (Due to intense volcanic activity & meteorite strikes)

• Higher concentration of CO2

  (Probably due to emission from volcanoes)

• Higher temps

• High levels of ultraviolet light penetration

The pre-biotic formation of Carbon Compounds

Formed spontaneously by chemical processes that do not occur today

Why conditions on Earth today make spontaneous formation of organic carbon compounds less likely than they were

• higher O2 levels (0% to 20%) causing the ozone layer to form

• Drop in CO2

• Reduction in greenhouse effect

Evidence that cells are living

• Cells use ATP energy to maintain highly ordered state

• Cells can divide or reproduce on their own to make new cells

• Cells can evolve

• Cells are separate from their environment but can still communicate with other cells

• Cells can receive and respond to stimuli

Why are viruses are considered non-living

• Non-cellular and lack organelles to carry out metabolism and protein synthesis independently

• Can only replicate in living cells using their components

3 common features of cells

1. A stable, semi-permeable membrane

2. Genetic material able to be passed on

3. Metabolic processes that allow ATP energy generation (enables growth, reproduction and self-maintenance)

Origin of carbon compounds

Molecules were mainly made up of C H O, some N P S

Living things make these by action of enzymes in their cells

Synthesis of simple organic molecules needed to occur for non-living materials to = life

Miller-Urey Experiment

Passed steam through a mixture of H2 and CH4 and NH3

Used electrical discharge to simulate lightning

Amino acids, fatty acids and sugars were produced

Spontaneous formation of vesicles

By coalescence (merging) of fatty acids into spherical bilayers

Importance of phospholipids in the formation of cells & their components

If phospholipids were part of the carbon compounds on pre-biotic earth, they would have self-assembled into bilayers and vesicles would likely have formed

Why was RNA was presumed as the first genetic material in living organisms and not DNA

• Can form as an enzyme

• Can act as a catalyst

• Can replicate

• Earliest life forms may have used it to store genetic material (RNA world hypothesis)

LUCA

• All life forms share a common ancestor

• Likely that other forms of life evolved at the same time, but became extinct

What is evidence for LUCA

Characteristics:

• Anaerobic (survived without oxygen)

• Carbon fixing (convertesd CO2 into glucose)

• Hydrogen dependent

• Nitrogen fixing (converted N2 into NH3)

• Thermophilic (survived high temps)

Outline the cell theory

• Cells are the smallest unit of life

• All organisms are made of cells

• All cells come pre-existing cells

Outline cells as the base of all living things

The cell is the basic structural, functional, and biological unit of all living organisms

Can be multicellular or unicellular

Calculating the magnification, size or actual size of an image

Magnification = size of image / actual size of specimen

1mm = 1000um

Light microscopes

Simple (1 lens), compound (2 lenses: ocular lens and objective lenses)

Can magnify up to ~1500x

4× 10× 40x

Max resolution: 0.2um (200nm)

Reveals only the structure of the cell

Electron microscopes

Scanning, transmission

Can magnify up to ~1,000,000x (1mill)

Uses beams of electrons to cause shorter wavelengths (more energy = more resolution)

Resolution: 0.001um (1nm)

Reveals the ultra structure of cells

Developments in microscopy

• 17th century, lenses were used

• 1665, the cell was named

• 1670: first living cell was seen

• 1931: Germans invented light microscopes

3 structures common to cells in all living organisms

• Cell membrane

• Cytoplasm

• DNA

Atypical Cell

Organisms that do not follow the typical structure and patterns in a eukaryotic cell

Describe the origin of eukaryotic cells by endosymbiosis

Began as prokaryotic cells, but were swallowed up by other prokaryotes until they became eukaryotes (gained mitochondria and or chloroplasts)

3 features that distinguish Eukaryotic cells from Prokaryotic cells

1. Nucleus

2. Ribosomes (different sizes)

3. Mitochondria

Advantages to Multicellularity

Multicellular organisms:

• Tend to have a longer lifespan

• Are generally larger than unicellular

• Are more complex

Processes required for the survival of organisms

• Homeostasis (constant internal environment)

• Metabolism (sun of biochem rxns)

• Nutrition

• Excretion

• Growth

• Response to stimuli

• Reproduction

What kind of environment did LUCA live in?

• High concentration of H2 CO2 and Fe

• Conditions found in and around hydrothermal vents

• Most suited to life were the alkaline hydrothermal vents (white smokers)

Slime Capsule (Glycocalyx)

Thick polysaccharide layer used for protection against desiccation (drying out) and phagocytosis

Phagocytosis

When a cell eats / consumes another cell

Naked DNA (P)

Usually only 1 DNA strand that is circular or forms a loop

Not associated with histone proteins

Plasmid (P)

Independent circular DNA molecule that may be transferred between bacteria (horizontal gene transfer)

DORA

• DNA:

  • P- DNA is naked, it is circular, usually has no introns

  • E- DNA is bound to protein, linear, usually has introns

• Organelles:

  • Not membrane bound vs membrane bound, 70S vs 80S, no nucleus vs nucleus

• Reproduction:

  • P- Binary fission, single chromosome

  • E- Mitosis and meiosis, chromosomes paired

• Average Size:

  • P- (~1-5um) E- (~10-100um)

4 types of Atypical cells

• Red blood cells

  • Do not have a nucleus

• Phloem Sieve Tube Elements

  • No nucleus and lack many other organelles

  • Have sieve tubes, each of which is connected to a companion cell which helps the element survive

• Skeletal Muscle

  • Cells fuse together to make a multinucleated cell

• Aseptate Fungal Hyphae

  • Fungi have thread-like structures called hyphae that are separated into cells by septa

  • These have NO septa = multinucleated

Endosymbiotic Theory

Mitochondria and Chloroplasts were once prokaryotic but were engulfed by larger prokaryotes via phagocytosis

Animal Cells = Mitochondria

Plant Cells = Mitochondria and Chloroplasts

Cell Differentiation

• Stem cells can become anything (turn into specialized cells)

• Only express genes that code for the required proteins

Housekeeper Genes

• genes that are always needed in a cell

• Regulate processes required (ex. metabolism, growth, DNA replication, transcription)

Protocell

It is a compartment enclosed in a phospholipid membrane.

It is likely that self-replicating molecules were encapsulated by this membrane