cell structure

Difference between eukaryotic cells and prokaryotic cells 3?

Eukaryotic cells are more complex, contain membrane bound organelles and have their DNA in the form of chromosomes within a nucleus

Structure of a nucleus?

Contains genetic information in the form of chromosomes, contains a structure known as a nucleolus, surrounded by a nuclear envelope (double membrane) containing pores

Function of a nucleus?

Controls the cell’s activities as it contains DNA with instructions to produce proteins, synthesis or ribosomes as the nucleolus makes ribosomal RNA, Exchange between nucleus and cytoplasm as substances can enter or leave via the pores

Structure of cell surface membrane?

Found on the surface of animal cells and mainly made up of lipids and proteins

Functions of cell surface membrane?

Controls movement of substances into and out of the cell as it is partially permeable, cell signalling receptors can detect signals from other cells

Structure of mitochondria?

Contain and enzyme rich liquid known as the matrix, surrounded by a double membrane in which the inner membrane is folded to form structures known as cristae, contain their own DNA and ribosomes

Function of mitochondria?

Site of aerobic respiration and produce ATP

Structure of ribosomes?

Made up of proteins and rRNA, consist of a large and a small subunit, not surrounded by a membrane

Function of ribosomes?

Site of protein synthesis and involved in translation

Structure of the golgi apparatus?

Contain fluid filled membrane bound sacs known as cisternae,contain smaller vesicles

Functions of golgi apparatus?

Process and package lipids and proteins , store and transport lipids and proteins, synthesise lysosomes

Rough endoplasmic recticulum structure?

Contains a network of membranes enclosing a fluid filled space known as cisternae, the surface of the cisternae is covered with ribosomes

Function of RER?

Synthesis and transport of proteins

Smooth endoplasmic recticulum structure?

Same as the rough endoplasmic recticulum

Function of SER

Synthesis store and transport lipids and carbohydrates

Structure of lysosomes?

Contain hydrolytic enzymes,surrounded by a membrane to keep enzymes seperate from the cytoplasm of the cell

Function of lysosomes?

Digest pathogens using enzymes, break down waste material such as old organelles and cells

What is the structure of cell walls?

Made up of cellulose, contains channels known as plasmodesmata

Function of cell walls?

Supports the cell as the contents of the cell press against the cell wall to make it rigid, prevents the cell from bursting as it can withstand high osmotic pressure, allows exchange of substances between cells as plasmodesmata connects neighbouring cells

Structure of chloroplasts?

Contain fluid filled sacs known as thylakoids which are stacked up to form grana, surrounded by a double membrane enclosing a fluid known as stroma, contain their own DNA and ribosomes

Function of chloroplasts?

Site of photosynthesis which take place in grana and stroma

What is the structure of a vacuole?

Contains cell sap, surrounded by a selectively permeable membrane known as a tonoplast

What is the function of a vacuole?

Helps to maintain pressure within the cell which keeps the cell rigid and stops the plant from wilting

Algal cells structure?

Contain the same organelles as plant cells, contain chloroplasts with different shapes to those found in plant cells

Fungal cell structure?

Contain most of the organelles found in plant cells,do not contain chloroplasts, contain cell walls made of chitin not cellulose

What are specialised cells?

Cells with certain features that allow them to carry out a particular function

What is squamous epithelium

A tissue that provides a thin lining for many organs such as the lungs. The tissue is made up of a single layer of squamous epithelial cells and allows for gases to diffuse quickly

What is ciliated epithelium?

Tissue that lines organs such as the trachea where it can sweep mucus away from the lungs. It is made of ciliated epithelial cells and goblet cells and the goblet cells release mucus to trap pathogens whilst the ciliated epithelial cells use cilia to sweep the mucus away

What is cartilage?

A type of connective tissue that acts as a cushion between bones and also provides support to organs such as the ears and nose. This tissue is made up of chondrocyte cells fixed within an extracellular matrix

What is muscle tissue and the three types?

It is made up of muscle fibres which contract and relax to move different parts of the body. The three types are smooth which are found in the walls of organs, cardiac found in the heart and skeletal found attached to bones

What is xylem tissue function and structure?

It is responsible for the transport of water and minerals within plants. It is made up of dead xylem vessel cells which have no end walls and no organelles. This forms a continuous column through which water can flow. The walls of these cells are strengthened by a waterproof material known as lignin

What is the function and structure of the phloem?

It is responsible for the transport of sugars and amino acids within plants. It is made up of columns of sieve tube elements and companion cells. The sieve tube element cells are separated by sieve plates with holes so that sugars can pass through. Sieve tube elements contain very few organelles allowing sugars to flow easily. Companion cells contain many mitochondria to release energy’

Name three more differences between eukaryotic cells and prokaryotic cells?

The cell wall in prokaryotic cells is made of murein not cellulose, ribosomes are 70S in prokaryotes and 80S in eukaryotes, the prokaryotes may have smaller loops called plasmids and large circular strands of DNA not a nucleus

Explain the extra features of a prokaryote?

Capsules- an extra layer around the cell wall made of polysaccharides and protects the cells from attack by antibiotics or white blood cells

A flagellum which is a long hair like structure attached to the cell membrane and rotates to push the cell through its environment

Pili are short hair like structures on the cell surface and are used for attaching prokaryotic cells to other cells or surfaces

Describe a virus?

A microscopic infectious acellular agent that can only replicate inside the cells of living organisms

What two parts are always present in a virus?

Genetic material- viral genome with either DNA or RNA

Capsid- a layer of protein molecules that surrounds and protects the genetic material

What three parts of a virus are sometimes present?

Envelope- an outer layer made up of phospholipids

Attachment proteins- help viruses to bind to host cells

Enzymes- some viruses carry enzymes like reverse transcriptase which allows them to convert RNA into DNA

Describe how viruses replicate?

The virus uses its attachment proteins to bind to complementary receptors on host cell. The virus injects its viral DNA or RNA into the host cell. The virus uses the host cell’s resources such as enzymes to replicate viral particles. New viral particles are assembled and released from the host cell

What is magnification?

How many times larger an image is than the object

What is resolution?

The ability to distinguish between two separate points

Equation for magnification?

Magnification= image/ actual

What is the resolution and magnification of a light microscope?

Resolution= 0.2 micrometres

Magnification= 1500x

How do you prepare a wet mount?

Use a pipette to place a small drop of water onto the centre of the glass slide. Use a pair of forceps to place a thin section of the specimen that is thin enough to allow light to pass through onto the drop of water. Add a few drops of stain such as iodine to the specimen to increase the contrast and allow cell components to become visible. Slowly add a cover slip onto the specimen with a mounting needle

List three other ways for sample preparation

Dry mount, squash slides, smear slides

Steps for using a microscope slide?

Clip the prepared microscope slide onto the stage, select the objective lens with the lowest power, use the coarse focus to bring the stage just below the objective lens, look down the eyepiece and use the coarse focus to move the stage downwards until the image is roughly in focus, use the fine focus to make the image clearer, if a higher magnification is needed swap to a more powerful objective lens and refocus

Why do electron microscopes have a better resolution?

Because they have a shorter wavelength than light

What are artefacts?

Visible details that aren’t part of the specimen being observed such as air bubbles or fingerprints

How do TEMs work? And their resolution and magnification

They use electromagnets to transmit a beam of electrons through a specimen. The denser parts absorb more electrons so appear darker in the image formed. Specimen must be viewed in a vacuum so only dead organisms can be observed and it must be really thin to allow electrons to pass through. They have a higher resolution of 0.5nm and magnification of 1500000x

How do SEMs work and their magnification and resolution?

They scan a beam of electrons across the surface of a specimen and reflected electrons are then used to form an image. They produce 3D images of the surface of the specimen and can view thicker specimen. Resolution 5nm magnification 1500000x

What is cell fractionation used for?

To isolate different components of the cell so they can be studied

Steps of cell fractionation?

1. Sample preparation- place the sample in a cold (to slow down enzyme activity that may breakdown the organelles), isotonic ( makes sure the water potential inside and outside the organelles is the same preventing damage caused by water movement), buffered (keeps the pH constant to prevent denaturation of enzymes)

2. Homogenisation- involves breaking the cell open by blending it which disrupts the plasma membrane and allows the organelles to be released into the solution

3. Filtration- the mixture is then filtered using gauze to remove larger pieces of cell debris and any remaining tissue fragments

4. Ultracentrifugation- seperates the organelles based on their densities by spinning the filtered solution at various speeds so they are separated into the pellet ( the sediment at the bottom of the tube containing heavier organelles) and the supernatant ( the liquid remaining above the pellet containing the lighter organelles)

Order of organelles from heaviest to lightest?

Nuclei, chloroplasts, mitochondria, lysosomes,ER, ribosomes

What are the three main phases of the cell cycle?

Interphase- which involves cell growth, synthesis of proteins and replication of DNA, mitosis, cytokinesis

What are the first 22 pairs of chromosomes in a human called

Autosomes as they are identical in both male and female

Describe the structure of a chromosome?

Two sister chromatids held together by a centromere

What are diploid cells?

Cells that contain two copies of each chromosome one from each parent

What are haploid cells?

They only contain one copy of each chromosome

5 ways mitosis is used?

Growth, replacement of damaged or dead tissue, asexual reproduction, development of body plans, production of stem cells

Stages of mitosis?

Prophase- chromosomes condense and become visible, centrioles move to opposite poles of the cell and start to form spindle fibres, the nucleolus disappears and the nuclear envelope dissolves leaving chromosomes free in the cytoplasm

Metaphase- the chromosomes line up at the equator of the cell, each chromosome attaches to the spindle by their centromere

Anaphase- the centromeres divide to separate each pair of sister chromatids, the spindle fibres contract and shorten to pull the chromatids to opposite poles of the cell, each chromatid is pulled by its centromere causing them to take on a V shape

Telophase- the chromatids reach the opposite poles of the cell where they uncoil to become long and thin chromosomes again, a nuclear envelope forms around each set of chromosomes to form two nuclei and the nucleolus starts to reform

What happens in cytokinesis?

The cytoplasm divides producing two identical daughter cells

What stages to cancer preventing drugs target of the cell cycle?

S phase where some drugs can prevent DNA from replicating, metaphase- some drugs interfere with the formation of spindle fibres

What are the five steps of binary fission?

1. Cell growth

2. DNA replication- the circular chromosome is replicated once and the plasmids may be replicated multiple times

3. Movement of DNA- each replicated circular chromosome moves to opposite poles of the cell and plasmids are distributed randomly between the poles

4. Cell wall growth- the cell surface membrane starts to divide and new cell walls form between the two DNA molecules

5. Cytoplasm division- the cytoplasm of the original cell is divided into two identical daughter cells

How do you calculate the bacterial population growth?

Time period/mean division time to get divisions then do starting cells times by 2 to the power of divisions

What are the optimal conditions for bacterial growth?

Warm, moist and lots of nutrients