Unit 1: Cells

What is a cell?

A separate living compartment where chemical processes occur

What is the function of the nucleus?

• Contains genetic material

• Controls cell growth and reproduction

What is the nuclear envelope?

A double membrane that separates the the nucleus from the cytoplasm.

What is the function of the nuclear envelope?

* Helps maintain the shape of the nucleus
* Regulates the flow of molecules into and in and out of the nucleus through nuclear pores

What is the nuclear envelope attached to?

Endoplasmic reticulum (ER)

What is the function of the smooth ER?

Synthesise lipids which are transported to the golgi apparatus by vesicles.

What is the function of the rough ER?

Protein synthesis

What is the function of the mitochondria?

Aerobic respiration to produce ATP

What is the function of chloroplasts?

Light dependent photosynthesis

What is the function of the golgi apparatus?

* Processes and modifies lipids and proteins from the rough ER
* Makes lysosomes

What is the function of the nucleolus?

To produce ribosomes

What are plasmids?

Small rings of DNA

What is the function of plasmids, linear chromosomes, looped DNA?

To carry genes

What is the function of the cell surface membrane?

* Hold the cell together
* Control the movement of substances in and out of the cell

What is the function of golgi vesicles?

To store lipids and proteins and transport them out of the cell

What is the function of the cell wall?

To protect and support the cell

What is the function of lysosomes?

Contain lytic enzymes to break down cell waste

What is the function of ribsomes?

Protein synthesis

What is the function of vacuole?

* In plant cells they maintain water balance
* In animal cells they store nutrients and waste materials until the cell gets rid of them

What is the function of the cytoplasm?

Site of metabolic reactions

What is the function of the trans face of the golgi appartatus?

To release the proteins or lipids after package

What is the function of the cis face of the golgi appartatus?

Receives vesicles from the RER

What is the function of the slime capsule?

To protect the cell

What is the function of the flagellum?

Movement

What is exocytosis?

Materials are exported out of the cell

What is the cristae?

Folds in the inner membrane of the mitochondria

What is the function of the cristae?

To increase SA

What is a matrix?

Gel-like material in the mitochondria

What is the function of the matrix?

Contains enzymes involved in respiration

What does specialised mean?

Adapted to perform a specific function

Name an example of a specialised cell

Epithelial cell in the small intestine

How are epithelial cells in the small intestine specialised for their function?

* Microvilli- increases SA
* Lots of golgi vesicles- to take transport proteins to the cell surface membrane
* Lots of mitochondria- to provide energy (ATP) for active transport

What are eukaryotic cells?

Cells with a nucleus

* Multi cellular organisms e.g plants, animals, fungi, protists.

What are prokaryotic cells?

Cells without a nucleus

* Single-celled organisms e.g fungi.

What are some differences between prokaryotic and eukaryotic cells?

* Eukaryotic cells have membrane bound organelles whereas prokaryotic cells do not
* Eukaryotic cells have bigger ribsomes than prokaryotic cells
* Eukaryotic cells have linear DNA bound in a nucleus but in prokaryotic cells it is free floating as circular plasmid DNA or chromosomal DNA
* Prokaryotic cells are much smaller than eukaryotic cells
* Prokaryotic cells are single-celled while eukaryotic cells can be multi cellular
* Prokaryotic cell wall is made of murein whereas the eukaryotic cell wall is made of cellulose
* Prokaryotic cells have a flagella but eukaryotic cells only have it sometimes
* Prokaryotic cells have pili but eukaryotic cells do not

What is magnification?

The process of enlarging the physical appearance/image of something

What is the maximum magnification of a light microscope?

x1500

What are the two lenses on a microscope?

Objective lens and eyepiece lens

How do you find the total magnification?

Magnification of the objective lens x magnification of the eyepiece lens

What is resolution?

The ability to distinguish between two points as separate structures

Magnification equation

Magnification = image size ÷ actual size

What are the two types of microscope?

Optical (light) and electron

What are the two types of electron microscope?

Transmission and scanning

Compare optical and electron microscopes

* Optical microscopes have a low resolution/magnification whereas electron microscopes have high resolution/magnification
* Optical microscopes produce coloured images while electron microscopes produce black and white images
* Optical microscopes can use living specimens (to view life processes like mitosis) whereas electron microscope specimens must be dead since they need to be in a vacuum
* Electron microscopes produce artefacts but optical microscopes do not

What are artefacts?

False objects mistaken for real features

Why does an electron microscope have a high resolution?

Because electrons have a short wavelength compared to light waves

Compare SEMs and TEMs

* SEMs produce a 3D surface image whereas TEMs produce a 2D internal image
* TEMs require a thin specimen but SEMs do not
* SEMs have a low magnification and resolution whereas TEMs have a very high magnification and resolution

What is differentiation?

Making cells adapted to carry out a particular function/job

What is a tissue?

Group of cells

What is an organ?

Group of tissues

What is an organ system?

Group of organs

What is an organism?

Group of organ systems

How does cell fractionation separate organelles?

Density

What are the 3 stages of cell fractionation?

1. Homogenisation
2. Filtration
3. Differential centrifugation

What is homogenisation?

The breaking up of cells

What happens during homogenisation?

The sample is homogenised using a homogeniser (blender) to break up the cell

What 3 conditions must be sample be?

1. Ice cold
2. Isotonic
3. pH buffered

Why must the sample be ice cold?

To reduce enzyme activity

Why must the sample be isotonic?

To prevent osmosis from happening, so osmotic lysis doesn’t occur

Why must the sample be pH buffered?

To avoid damaging protein structures

What happens during filtration?

The homogenate is filtered into tubes through a gauze to remove debris

What happens during differential centrifugation?

* Sample is spun at a low speed to separate it into fractions
* The organelles form a pellet at the bottom of the tube, leaving the supernatant (liquid)
* The supernatant is centrifuged at gradually increasing speeds to separate the least organelles

What density are the organelles separated at a low speed?

Very dense

What density are the organelles separated at a high speed?

Not very dense

Order the organelles from most to least dense

Nucleus

Chloroplasts

Mitochondria

Lysosomes

Endoplasmic reticulum

Ribosomes

How do prokaryotes reproduce?

Binary fission

Describe the process of binary fission

1. Circular DNA and plasmids replicate
2. Cell gets bigger and the circular DNA strands move to opposite poles of the cell
3. Cytoplasm begins to divide and new cell walls begin to form
4. Cytoplasm divides and two new identical daughter cells are produced

What are the 3 stages of the cell cycle?

1. Interphase (G0, G1, S, G2)
2. Mitosis (PMAT)
3. Cytokinesis

What is the centromere?

Links a pair of sister chromatids

What is a chromatid?

One half of a replicated chromosome

What does the centriole do?

It produces spindle fibres

What happens in the G0 stage of the cell cycle?

Resting state for non-dividing cells

What happens in the G1 stage of the cell cycle?

Growth of the cytoplasm and organelles

What happens in the S stage of the cell cycle?

DNA synthesis

What happens in the G2 stage of the cell cycle?

* Mitochondria and ATP synthesis
* Cell ‘double checks’ the duplicated chromosomes for errors and makes any necessary repairs

What are the 4 stages of mitosis?

**P**rophase

**M**etaphase

**A**naphase

**T**elophase

What happens during prophase?

* Chromosomes condense and become visible
* Centriole divides and moves to opposite poles of the cell
* Nucleolus becomes less prominent
* Nuclear envelope disintegrates

What happens during metaphase?

* Each centriole is at a pole
* Centrioles produce spindle fibres
* Spindle fibres attach to the centromere of the chromosomes
* Chromosomes line up at the equator

What happens during anaphase?

* Spindle fibres contract (requiring ATP)
* Chromatids are pulled to opposite poles of the cell

What happens during telophase?

* Chromatids reach the poles of the spindle
* Chromatids begin to uncoil and become less distinct
* Nuclear envelope starts to reform

What happens during cytokinesis?

The cell divides

Why do cells need to divide?

To produce new cells

* For growth
* For replacement of old/damaged cells

To reproduce

* Asexual reproduction (cloning)
* Sexual reproduction (gametes)

What are the steps to finding how much time a cell spends in mitosis?

1. Find total number of cells
2. Work out number of cells in specific stage as a percentage of the total
3. Work out time spent in that stage by calculating same percentage of 24 hours
4. Convert answer to minutes and hours if necessary

What is the equation to calculate mitotic index?

Cells undergoing mitosis ÷ total number of cells

What form will a mitotic index be in?

Percentage or decimal

What is a virus?

Non-living structures which consist of one or more strands of genetic material (DNA or RNA) surrounded by a protein coat (capsid).

What structures is a HIV virus made up of?

* Attachment protein
* Lipid envelope
* Matrix
* Capsid
* DNA/RNA
* Reverse transcriptase (enzyme)

How does HIV replicate after entering a human cell?

1. HIV attaches to the complementary proteins on the surface of the helper T-cell and the virus enters the cell.


1. Reverse transcriptase converts the viral DNA to RNA.
2. This DNA is then joined into the DNA of the host cell.
3. When the host cell divides the DNA is used to make copies of HIV RNA.
4. The HIV capsid (protein) and enzymes and made by host cell ribosomes.
5. Everything is assembled by the host cells RER and golgi apparatus into new virus particles.
6. These are packaged into vesicles and ‘budding off’ occurs (viruses are wrapped in a membrane).

Why are antibiotics ineffective against viruses?

They prevent chains/bonds being made in the cell walls but since viruses do not have cell walls they do not work.