Cell Structure

Question 1

Cell Membrane

Answer 1

→ Semi-Permeable Membrane of the cell (Separates inside from outside)
↑ Cells are small because this cell wall has to have enough surface area for diffusion and osmosis (Remember the volume to surface area ratio decreases as things get bigger)
→ Made of a phospholipid Bilayer. Have a phosphate head and a fatty acid tail.
↑ The head is hydrophilic and the tail is hydrophobic.
↑ That is why they are so good at separating the inside of the cell from the outside.

Question 2

Cell Membrane: Integral Protein

Answer 2

Protein that goes through the cell wall. These proteins are essential for cell transport and give the cell membrane that semi-permeable property.

Question 3

Cell Membrane: Peirphiral Protein

Answer 3

Protein that is on the cell membrane, either inside the cell or outside. There functions can range from providing cell structure to speeding up reactions.

Question 4

Cell Membrane: Cholesterol

Answer 4

Used to maintain spacing between the lipids in the lipid bilayer, when temperature increases or decreases. Remember that the cell membrane is usually moving according to the fluid mosaic model.

Carbohydrates are biomolecules that consist of Oxygen, Carbon and Hydrogen

Question 5

Cell Membrane: Glyco Proteins or Glyco Lipids

Answer 5

Sometimes Carbohydrates attach to peripheral proteins or lipids on the membrane and they are called Glyco Proteins/Lipids.
→ Helps Identify the cell
→ Important for cell signalling

Question 6

Cell Membrane Functions Summary:

Answer 6

→ Provide Structure
→ Cell Transport
→ Ways to interact with other cells
→ Let certain things in and out

Question 7

Nucleus

Answer 7

The nucleus can be thought of as the control center of the cell.
→ It houses the chromosomes
→ DNA is transcribed(Copied in a process) to make RNA

Most cells have one nucleus however some are so big that they have two nuclei (Muscle and Skeletal).

Question 8

Nucleus: Nuclear Envelope

Answer 8

The Nuclear envelope is made of an outer and inner membrane
↑ They are both lipid bilayers. However, the inner layer has a fibrous protein called the lamina, and that helps with the structure of the chromatin.
→ Helps separate the inside of the nucleus from the rest of the cell.
↑ This helps protect the nucleus from all the harmful enzymes and the cytoplasm.

Question 9

Nucleus: Nuclear Pore

Answer 9

These pores span the inner and outer membrane. They regulate what comes in and what goes out based on special sequences (semi-permeable).

Question 10

Nucleus: Nucleolus

Answer 10

The nucleolus is the center of the nucleus
→ More compact and dense than the rest of the nucleus (Contains RNA and proteins)
→ The Nucleolus produces new ribosomes
↑ The densely packed DNA produces Ribosomal RNA(This RNA makes up most of the ribosome)
↑ Proteins made in the cytoplasm that comes via nuclear pores are added to make a fully-formed ribosome.

Question 11

Endoplasmic Reticulum

Answer 11

Called the highway of the cell. Found in plants and animals, not in bacteria

There are two parts: Rough E.R and Smooth E.R

Question 12

Endoplasmic Reticulum: Rough E.R

Answer 12

The Rough E.R is lined with Ribosomes. These Ribosomes further synthesize proteins that have started to form from free-floating ribosomes.
↑ The proteins are specialized (post-translation) in the Rough E.R from a signal sequence that gets attached to them from the free ribosomes.
→ From there, they follow the secretory pathway via Vesicles, Lysosomes, Golgi Apparatus.
→ Attached to the nucleus so that it can get the necessary mRNA.

Question 13

Endoplasmic Reticulum: Smooth E.R

Answer 13

Synthesizes lipids using enzymes
→ These lipids might be used for the cell membrane or might be secreted
→ Metabolizes Carbohydrates
→ Detoxifies drugs with oxidation reactions
→ Transport protein from Rough E.R to the Golgi Apparatus. The actual transport from Smooth E.R to Golgi Apparatus is done by vesicles.
→ Has an enzyme responsible for making glucose

Question 14

Ribosomes

Answer 14

Site for protein synthesis
→ It is made of RNA(called ribosomal RNA) and proteins
→ It reads RNA and synthesizes protein by bringing the right amount of amino acids together to make polypeptides(structure of proteins).

It is divided into 2 subunits: Small and Large Subunits
→ Both subunits contain protein and RNA

Question 15

Two types of Ribosomes

Answer 15

Free-floating and Apart of the Rough E.R are the two types of Ribosomes

Free-floating
→ Synthesize protein for inside the cell

Apart of Rough E.R
→ Synthesizes proteins to be secreted.

Question 16

Golgi Apparatus

Answer 16

Stores, modifies, packages proteins and lipids that need to leave the cell.
↑ The Golgi get these proteins from the E.R via a transport called Cop 2 protein
↑ They are transported out of the cell via vesicles
→ The Golgi also adds sugar to the proteins and adds carbohydrates to some
↑ It will also add a signal sequence to tell the protein where it should be.

It also has two faces: Cis Face and Trans Face

Cis face - receiving face (gets proteins) [facing the E.R]
Trans face - shipping face (secreting proteins) [facing cell wall]

Question 17

Lysosomes

Answer 17

These have digestive enzymes that help digest waste molecules or substances.
This digestion will usually break the molecule down into its most basic components (So proteins break down into amino acids)
→ The inside of a lysosome is acidic with a pH of 5
→ The enzymes in the lysosomes responsible for the digestion are called “acid hydrolases”
↑ They have acid in the name as they need an acidic environment to function.
↑ This is important so that if these lysosomes burst, the enzymes will stop working as the cytoplasm has a neutral ph of 7.4. That way these enzymes don’t digest the entire cell.
↑ However, if enough lysosomes burst and the cytoplasm becomes acidic, then the cell will self-destruct.

Question 18

Lysosomes: “Autophagy”

Answer 18

Meaning “self-eating”
→ Digests molecules that are a part of the cell or other cells
↑ Organelles that no longer function will be digested through Autophagy.

Question 19

Lysosomes: “Crinophaghy”

Answer 19

A process where the lysosomes digest excess secretory products.

Question 20

Mitochondria

Answer 20

A powerhouse of the cell, Cellular respiration occurs in the mitochondria (ATP factory).

→ Has two layers (both phospholipid bilayers).
Inner Membrane:
→ Not permeable
→ Has many folds called crista or cristae for plural.
↑ This increases surface area for cellular respiration

Outer Membrane:
→ Has proteins that make is semi-permeable to very small molecules

The space on the inside of the inner membrane is called the matrix

Question 21

Cellular Respiration (Aerobic)

Answer 21

How ATP(Energy currency) is made.

Can produce 30-38 molecules of ATP from the process.

Question 22

Cellular Respiration: Glycolysis [Step 1]

Answer 22

→ Takes place in the cytoplasm
→ Anaerobic (does not need oxygen)
→ Glucose is converted into a more usable form, pyruvate
↑ Also produces ATP and some NADH

NADH are enzymes that can transfer electrons

Pyruvates are transported to the mitochondrial matrix where it is converted to Acetyl CoA by oxidation.
↑ Carbon Dioxide is released
↑ 2 NADH are formed

Question 23

Cellular Respiration: Krebs Cycle [Step 2]

Answer 23

→ The aerobic process takes place in the mitochondrial matrix

Acetyl CoA becomes
↑ CO2 (which is released)
↑ 2 ATP
↑ 6 NADH
↑ 2 FADH (also electron transfer enzymes)

Question 24

Cellular Respiration: Electron Transfer Chain or Chemiosmosis [Step 3]

Answer 24

→ Aerobic
→ Uses an enzyme called ATP synthase which uses H+ ions to make ATP and water.
↑ H+ ions pass through the enzyme due to an electrical and chemical imbalance.

This all happens in the inner mitochondrial membrane.

Question 25

ATP

Answer 25

The full-form is Adenosine Triphosphate.
→ Energy currency for the cell

The phosphate bonds are very unstable (low activation energy)
→ So when the third phosphate bond breaks, energy is released chemically.
→ This happens in a hydrolysis reaction (a reaction that requires water).
ATP → ADP + Energy
ADP is Adenosine Diphosphate

Question 26

Chloroplast

Answer 26

An organelle is only found in a plant cell. Responsible for photosynthesis.

Has stacks of thylakoid called grana
→ A Thylakoid stores chlorophyll
→ Lumen inside
→ Stroma surrounds.

Question 27

Chloroplast: Photosynthesis

Answer 27

1) Photon from the sun crashes into the chlorophyll and excites the electrons through photoexcitation. (Apart of Photosystem 2 protein complex)
2) Electron transport chain: The electrons are so excited that they get picked up by a protein electron carrier.
3) Since the chlorophyll is losing electrons, it gains them back by splitting H2O and forming 2 H+ and O. The H+ ion gets pumped into the thylakoid by the cytochrome complex
4) Since there is an imbalance in H+ concentration, it wants to balance. But to balance the H+ ion has to pass through an enzyme called ATP Synthase. ATP synthase harnesses the energy to make ATP

Chloroplasts can move around to adjust how much light they get.

Question 28

Cell Wall

Answer 28

Found only in plant cells and bacteria

→ It is a protective and rigid barrier that is located outside of the cell membrane.
↑ It is made of fibres like cellulose, hemicellulose and pectin.

Question 29

Vacuole

Answer 29

These are usually in less quantity and bigger size in a plant cell; smaller size and higher quantity in animal cells.

→ Have a membrane that is a phospholipid bilayer

In plants, vacuoles function to store
→ harmful materials
→ waste products
→ water used in photosynthesis
→ maintain hydrostatic pressure (This helps the cell to resist external forces)
→ Protein on the vacuole wall is pumping H+ inside to create a little acidic environment.

In animal cells, vacuoles function to
→ store water and waste products
→ Mainly helps with endocytosis and exocytosis

Question 30

Cilia

Answer 30

Cilia are hair-like projections that are attached to the cell and help the cell direct the flow of substances around the cell.

→ Can also act as sensory organs, sensing environmental cues.

Question 31

Flagella

Answer 31

A tail-like structure that helps the cell move around.