biology edexcel b seyi

Features and function of the Nucleus

• Present in all eukaryotic cells

• Surrounded by double membrane (nueclear envelope)

• Membrane contains nuclear pores to allow movement of mRNA and ribosomes out of nucleus, and enzymes into nucleus

• Stores genetic material as chromatin

• nucleolus (site of ribosome production)

Where is the site of ribosome production?

Nucleolus

Features and Function of Rough Endoplasmic Reticulum

• Folds of membrane with it's surface covered in ribosomes

• Folds and processes proteins made on the ribosomes

Features and Function of Smooth Endoplasmic Reticulum

• Folds of membrane (no ribosomes)

• Production, processing and storage of lipids, carbohydrates and steroids

How to distinguish between smooth or rough endoplasmic reticulum?

Observe under electron microscope

If ribosomes present, it is RER

If ribosomes not present, it is SER

Features and function of Golgi Apparatus

• Flattened Fluid filled curved sacs called cisternae

• Sorts and modifies proteins and lipids before packaging them into vesicles to be transported.

Features and function of mitochondria

• Site of aerobic respiration

• Surrounded by a double membrane (envelope)

• Inner membrane folded to form cristae

• Matrix contains enzymes needed for aerobic respiration

• Also contains ribosomes and small pieces of DNA needed for replication of mitochondria before cell division

Features and function of centrioles

• Not found in plant or fungi cells

• Made out of hollow fibres called microtubules

• Microtubules are filaments of a protein that is used to move substances inside the cell and supports shape of cell

• Two centrioles at a right angle to each other form a centrosome

• Organises spindle fibres during cell division

Features and function of 80s Ribsosomes

• Found in eukaryotic cells only

• Site of protein synthesis and translation

• Made up of large 60s subunit, and small 40s subunit

Features and function of lysosomes

• Bound by single membrane

• Form of vesicle containing hydrolytic enzymes

• Used by cells of immune system for programmed cell death

Features and function of vacuole

• Large and central in plants (animal cells may have one, but they are often small and temporary)

• Fluid filled cavity surrounded by a membrane (tonoplast)

• Helps maintain hydrostatic pressure and store cell sap

Features and function of plasmids

• Small loops of DNA sometimes found in bacterial cells

• Contain genes that can be passed between prokaryotes (antibiotic resistance)

Features and function of slime capsule

• Help keep bacteria moist and prevent them from drying out

• Help protect bacterial cells from attack of host organisms immune system cells

Features and function of Nucleoid

• Area in which circular DNA is found

• Genetic material in prokaryotic cells often found as single circular strands

Features and function of Pilus

• Thread like structures found on cell surface membrane

• Enables bacteria to attach to other cells and surfaces

• Allows plasmids to be passed from cell to cell

Features and function of 70s Ribosomes

• Large 50s subunit

• Small 30s subunit

• Site of protein synthesis

Features and function of cell wall (prokaryotic)

• Made of peptidoglycan

• Provides strength and support to the cell

Difference in structure of Gram negative and Gram positive bactera

Gram positive:

• Thick layer of peptidoglycan

• Inner plasma membrane

Gran negative:

• Thin layer of peptidoglycan

• Outer lipopolysaccharide membrane

Gram Staining Test Procedure + Results

1. Crystal violet solution for 1 minute, then wash with water

2. Iodine solution for 1 minute, wash with water

3. Alcohol added for 1 minute (lipopolysaccharide soluble in alcohols so outer membrane dissolves)

4. Red safranin for 1 minute, then dried

Gram positive: Purple

Gran negative: Pink/Red

Resolution

Minimum distance between two objects where they can still be seen as two separate objects

Features of transmission electron microscope

Beams of electrons transmitted through the object, producing a 2D image.

Resolution 2000x better than light microscope

Features of Scanning electron microscope

Beam of electrons scans back and forth over the surface of the sample producing a 3D image

What type of staining is required for electron and light microscopes?

Electron microscopes - heavy metals (reflect electrons)

Light microscopes - methylene blue

Ads of electron microscopy

Higher resolution and magnification

Disads of electron microscopy

• Sample must be placed in a vaccuum, therefore not living

• Expensive and not portable

• Produces only black and white images

What is the protective coat of Nucleic acid in viruses called?

Capsid

Describe the lytic cycle of a virus

1. Attachment - phage attaches to the surface of the host

2. Penetration - viral DNA/RNA is inserted into the cytoplasm of host call

3. Biosynthesis - Phage DNA replicated and phage proteins are made

4. Maturation - Phage particles assembled

5. Lysis - Lysis of cell releases newly made phages (independent of host cell's genome)

Describe the lysogenic cycle of a virus

1. Phage attaches to surface of host cell and inserts DNA/RNA in the form of a provirus

2. Viral DNA integrates with host cell/s DNA

3. Enables viral DNA to be replicated through cell division of host cell.

Provirus can remain dormant if virus produces repressor proteins, inhibiting the transcription of the provirus.

Ethical implications to using untested drugs

• Difficult to obtain informed consent

• Unknown side effects

• May not ending up being more effective than other existing alternatives/treatment

What are the 4 stages of mitosis?

prophase, metaphase, anaphase, telophase

Describe prophase

• Chromosomes condense (2 sister chromatids joined by a centromere

• Nuclear envelope breaks down

• Centrioles move to opposite poles forming spindle network

Describe Metaphase

• Chromosomes align along equator of the cell

• Spindle fibres attach to chromosomes by centromeres

Describe Anaphase

• Spindle fibres contract and pull chromatids to opposite poles of the cell

• Centromere divides

Describe Telophase

• Chromosomes uncoil and become chromatin

• Nuclear envelope forms around two sets of chromosomes

• Two nuclei that form are identical

Describe cytokinesis

• Cytoplasm divides

• Produces 2 daughter cells

Describe interphase

G1, S, G2 - DNA replication and preparation for cell division - chromosomes and some organelles are replicated

What is the main purpose of meiosis?

Production of haploid gametes

Maintenance of chromosome number