eukaryotic, prokaryotic cells, viruses + nucleus structure

Question 1

examples of eukaryotic organisms

Answer 1

plant
animal
fungi

Question 2

order of organisation

Answer 2

Specialised cells are organised
into tissues, tissues into organs and organs into systems.

In complex multicellular organisms, eukaryotic cells become
specialised for specific functions

Question 3

example of prokaryotic organisms

Answer 3

bacteria
archaea

Question 4

all living organisms can be divided into _____

Answer 4

eukaryotes/prokaryotes -> living organisms

Question 5

Describe the general structure of eukaryotic cells

Answer 5

In all eukaryotic cells,

the DNA is contained in a membrane-bound (surrounded by a membrane) nucleus

The nucleus has a double membrane

the DNA is tightly wrapped/coiled around proteins called histones

Together, the DNA and histone proteins form chromosomes

By tightly coiling their DNA into chromosomes, eukaryotic cells can pack a lot of DNA into their nucleus

Their DNA is a linear molecule (the ends of the DNA molecule in a chromosome are not joined together to form a loop)

Eukaryotic cells contain other membrane-bound organelles - mitochondria, Golgi apparatus, endoplasmic reticulum
The same organelles are in plant cells, but in plant cells, there are also chloroplasts and a vacuole (also membrane-bound organelles)

The presence of membrane bound organelles

Contain other organelles that are not membrane-bound. For example, ribosomes which are involved in protein synthesis

Eukaryotic cells - surrounded by a cell-surface membrane (helps to control the molecules that can pass in and out of the cell)

In plants and fungi - cell membrane - surrounded by cell wall (the cell wall helps to maintain the structure of these cells)
plant cells - made from polysaccharide - cellulose
fungal cells - polysaccharide chitin

https://www.genome.gov/sites/default/files/media/images/tg/Chromosome.jpg

Question 6

what does DNA and histone proteins form

Answer 6

Together DNA and histone proteins form chromosomes

Question 7

The DNA in eukaryotic cells is a linear molecule
What does this mean

Answer 7

Their DNA is a linear molecule (the ends of the DNA molecule in a chromosome are not joined together to form a loop)

Question 8

where are ribosomes found

Answer 8

eukaryotic and prokaryotic organisms/cells

Question 9

what is the difference between the ribosomes in eukaryotic cells and prokaryotic cells

Answer 9

The ribosomes in eukaryotic cells are larger than those in prokaryotic cells

eukaryotic cells contain 80S ribosomes

prokaryotic cells contain 70S ribosomes

S - a unit showing how quickly organelles move in a centrifuge

Question 10

describe how eukaryotic cells may lose their nucleus as they develop

what happens to most eurkaryotic cells

Answer 10

E.g. red blood cells in humans

most eukaryotic cells have a nucleus throughout their lifespan

Question 11

draw an animal cell

Answer 11

https://s3.eu-west-2.amazonaws.com/elements.cognitoedu.org/a873ae44-8320-4da5-95d5-5cfa390ff0b5/animal-cell-organelles-diagram.png

Question 12

draw a plant cell

Answer 12

https://s3.eu-west-2.amazonaws.com/elements.cognitoedu.org/2d24fe71-a463-47bf-8adb-09b05c963529/plant-cell-organelles-diagram.png

Question 13

draw a fungal cell

Answer 13

plant cell without chloroplasts

https://s3.eu-west-2.amazonaws.com/elements.cognitoedu.org/2d24fe71-a463-47bf-8adb-09b05c963529/plant-cell-organelles-diagram.png

Question 14

describe the structure of prokaryotic cells

Answer 14

Prokaryotic cells - much smaller than eukaryotic cells

Prokaryotic cells have no membrane-bound organelles

This means that in prokaryotic cells, the DNA is found in the cytoplasm rather than in a nucleus

Unlike in Eukaryotic cells, the DNA is arranged into a circular chromosome with no free ends and is not associated with
proteins

The DNA in prokaryotes is not bound to histone proteins

Sometimes bacterial cells contain small loops of DNA called plasmids

Plasmids usually contain a relatively small number of genes (these can include genes which make the bacterium resistant to antibiotics)

SO Plasmids are very important for bacteria (eukaryotic cells do not contain plasmids)

Prokaryotic cells contain ribosomes (70 S) -

prokaryotic cells - surrounded by a cell wall (in bacteria, this is made from peptidoglycan/murein - glycoprotein)
peptidoglycan - polymer formed between peptides and polysaccharide molecules

Cell wall helps to maintain the structure of the cells

Some bacteria produce a slime capsule on the outside of the cell wall - the slime capsule can help to protect the bacteria from phagocytosis by white blood cells

Some prokaryotic cells have a flagellum - helps them to move (flagellum - sperm -eukaryotic) - have different structures

pili - fine protein strands on their surface
these help bacteria to attach to surfaces/other bacteria
when two bacteria are attached, DNA can be transferred from one bacterium to another

bacteria also contain lipid droplets and glycogen granules - these act as nutrient stores for the bacterial cell

sometimes using the electron microscope - we can see infoldings in the cell membrane of prokaryotic cells - these are called mesosomes

initially scientists suggested that mesosomes played a role in respiration /// however scientists now believe that mesosomes are actually artefacts that are created when bacterial cells are prepared for electron microscopy

Question 15

Importance of plasmids in prokaryotic cells

Answer 15

Plasmids usually contain a relatively small number of genes (these can include genes which make the bacterium resistant to antibiotics)

Question 16

describe the importance of cell walls in prokaryotic/eukaryotic cells organisms

Answer 16

Cell wall helps to maintain the structure of the cells

E.g. if water moves into the bacteria cell by osmosis, the cell wall prevents the cell from bursting

Question 17

draw a bacteria cell

Answer 17

https://s3.eu-west-2.amazonaws.com/elements.cognitoedu.org/f4d1b75a-2e5d-4038-aebc-607efbbf4ace/prokaryotic-organelles-illustration.png

Question 18

describe the structure and life cycle of viruses

Answer 18

different types of viruses can have different shapes, but many viruses are broadly spherical

All viruses contain genetic material - this can be either DNA or RNA

The genetic material is contained inside a protein structure called a capsid

On the surface of the virus, are attachment proteins

These attachment proteins allow the virus particle to attach to and enter the host cell

In some viruses, the capsid is surrounded by a lipid envelope - lipid envelope formed from the host cell membrane

Question 19

DRAW A VIRUS

Answer 19

https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcTDvd7uBLPDxhB6jeqNm1HnC32aHW7thJTnsCdIPsqlY2PsOB-i

+ LIPID ENVELOPE - CIRCLE AROUND VIRAL PARTICLE

https://s3.eu-west-2.amazonaws.com/elements.cognitoedu.org/732822c4-1fa5-44f3-b4e9-e3c2966fb03e/virus-structure-diagram.png

Question 20

what can viruses not do independently

Answer 20

Viruses cannot reproduce independently
Viruses can only reproduce inside a host cell

Question 21

describe how viruses reproduce inside a host cell

Answer 21

A virus particle attaches to the surface of a host cell
Next the virus enters the host cell

Now, the virus uses the host cell’s enzymes to produce copies of itself

These virus particles now leave the host cell and can go on to infect new host cells and continue reproducing

Question 22

compare the difference in size of a bacterial cell and a virus particle

Answer 22

A virus particle is much smaller than a bacterial cell

Question 23

Viruses are not _____

Answer 23

Viruses are not cells
Viruses are acellular - which means not based on cells

Question 24

explain how viruses are not living

Answer 24

Viruses cannot reproduce independently - in order to reproduce, a virus must invade a host cell and use the host cell’s enzymes to make copies of itself

So because viruses cannot reproduce on their own, viruses are not counted as living organisms

Question 25

Draw the nucleus

Answer 25

https://studymind.co.uk/wp-content/uploads/2022/03/Screen-Shot-2022-03-29-at-3.54.23-PM.png

Rough Endoplasmic Reticulum
outer membrane
Inner membrane

Question 26

describe the structure of the nucleus in cells

Answer 26

The nucleus contains a jelly-like `material called nucleoplasm
Nucleoplasm contains molecules such as nucleotides and enzymes - which are needed for DNA and RNA synthesis

Surrounding the nucleus, is a double membrane. This is called the nuclear envelope
Consists of two phospholipid bilayers

Within the nuclear envelope, there are nuclear pores - Function of nuclear pores - to allow molecules to enter and leave the nucleus
e.g. RNA nucleotides enter the nucleus through nuclear pores from the cytoplasm/ These nucleotides are used in the nucleus to synthesise messenger RNA The MRNA then leaves the nucleus via a nuclear pore and undergoes translation on a ribosome

The outer membrane of the nuclear envelope is continuous with the rough endoplasmic reticulum (RER plays a role in protein synthesis)

Nucleus contains a dark material - called chromatin
Chromatin - consists of DNA coiled around proteins called histones.
Together, the DNA and histone proteins form chromosomes (DNA in chromosome is a linear molecule)

Chromosomes are not visible inside the nucleus unless the cell is undergoing mitosis or meiosis.

In the nucleus, there is a region darker than the rest. This is called the nucleolus. The nucleolus is where are special type of RNA is produced called Ribosomal RNA ( or rRNA)
Ribosomal RNA forms part of the structure of ribosomes.
As well as forming rRNA the nucleolus is also where ribosome subunits are assembled

nucleus can contain one or more nucleoli

Question 27

Chromosomes are not normally ______ inside the nucleus.
In what instant are they normally _______

Answer 27

Chromosomes are not visible inside the nucleus unless the cell is undergoing mitosis or meiosis.

Question 28

explain the importance of proteins to living organisms

Answer 28

enzymes are proteins
enzymes (biological catalysts) are required for chemical reactions taking place in cells

other proteins play a structural role in cells e.g. moving organelles to where they are needed

some proteins act as transport molecules - e.g. haemoglobin - transports oxygen in mammals

so protein synthesis is one of the most important functions taking place in cells

Question 29

describe protein synthesis

role of nucleus in protein synthesis

Answer 29

protein synthesis involves several different organelles

the instructions for encoding the amino acid sequence of a protein are contained within the gene for that protein

these genes are part of the chromosomes - which are found in the nucleus

to synthesise a protein, the genetic information encoded by that gene is converted to messenger RNA or mRNA - This process is called transcription

in nucleus (with pores)
gene –> mRNA (–> = transcription)

This mRNA then leaves the nucleus

now a ribosome reads the information contained in the mRNA and synthesises the protein molecule - called translation

mRNA –> protein (—> = translation by ribosome)

if the protein remains in the cytoplasm e.g. a cellular enzyme, then translation will take place on a free ribosome in the cytoplasm

However some proteins are secreted from cells e.g. digestive enzymes and antibodies
secreted proteins are translated on a ribosome attached to the rough endoplasmic reticulum

These proteins then make their way through the rough ER and the Golgi apparatus before leaving the cell

shows role of nucleus in protein synthesis