Cell structure and function

Question 1

prokaryotes cell size

Answer 1

1μm³

Question 2

eukaryote cell size

Answer 2

1000μm³

Question 3

plasma membrane

Answer 3

• surrounds the contents of the cell and defines its outer boundary
• acts as a barrier to the external environment but also has many other roles
• composed of lipids and proteins

Question 4

plasma membrane function

Answer 4

• control transport in and out of cell
• passes signals from the environment in the cell
• connects to other cells
• concentrates enzyme activity

Question 5

mitochondria

Answer 5

• large organelles
• responsible for producing energy for the cell
• can be thousands in energy demanding cells or just two or three in low energy cells
• can change shape and move around the cell
• can fuse with one another and then move apart again
• two membranes
• contain their own DNA
• centre matrix - site of biochemical reactions

Question 6

mitochondria inner membrane

Answer 6

• highly folded to increase surface area
• contains electron transport chain and ATP synthase molecules that make ATP during respiration

Question 7

Nucleus

Answer 7

• home to DNA - control centre of the cell

Question 8

DNA

Answer 8

organised into chromosomes and can adopt to chromatin

Question 9

chromatin

Answer 9

DNA bound to proteins that make RNA, repair DNA and copy DNA etc

Question 10

Nuclear pores

Answer 10

allow signals to enter the nucleus and mRNA to leave the nucleus

Question 11

chromosomes

Answer 11

• only visible during cell division
• mostly, DNA is unwound, allowing it to be read and transcribed
• some DNA cant read, some are silenced by epigenetic modifications

Question 12

Nucleolus

Answer 12

• region within the nucleus that is the site of ribosome biogenesis
• some cells have a single, large nucleolus while other cells can have several smaller nucleoli
• highly dynamic and can change overtime

Question 13

Ribosomes steps

Answer 13

• make proteins
  1) find the gene that codes for the protein in the nucleus
  2) copy the gene into mRNA (transcription)
  3) send the mRNA out of the nucleus
  4) the ribosomes read the sequence of mRNA and link together the appropriate individual amino acids to make the protein (translation)

Question 14

rough ER

Answer 14

• contain ribosomes, site of protein synthesis

Question 15

smooth ER

Answer 15

site of metabolic process such as steroid metabolism

Question 16

Golgi apparatus

Answer 16

• made up of membranes
• packages proteins into membrane bound parcels (vesicles) which are then transported to other parts of the cell for secretion

Question 17

What is phagocytosis?

Answer 17

• “Cell eating” – the cell engulfs large particles like bacteria or debris using pseudopodia.
• Forms a phagosome, which fuses with a lysosome for digestion.
• Done by immune cells like macrophages and neutrophils.

Question 18

What is pinocytosis?

Answer 18

• “Cell drinking” – the cell takes in extracellular fluid and dissolved solutes via small vesicles.
• It’s a continuous and non-specific process.

Question 19

What is receptor-mediated endocytosis?

Answer 19

• A selective process where specific molecules bind to cell surface receptors.
• The cell then engulfs the receptor-ligand complex in a vesicle.
• Example: cholesterol uptake via LDL receptors.

Question 20

Endosomes

Answer 20

• membrane enclosed vesicles that are created when the plasma membrane pulls large particles into the cell
• transported into the cell where they fuse with lysosomes

Question 21

lysosomes

Answer 21

• contain powerful degrative enzymes that breakdown proteins and other biological molecules into their constituent parts
• can be re used
• part of the cells recycling system

Question 22

cytoskeleton

Answer 22

• series of fibres that runs throughout the cell
• provides mechanical strength and support for the cells
• allows cells to change shape and move
• provides the cells transport system to move organelles and vesicles around
• separates chromosomes and splits cells in half during cell division

Question 23

vacuole

Answer 23

• take up a large fraction of the cell
• storage for water and nutrients
• helps maintain pressure on the cell wall

Question 24

cell wall

Answer 24

• provides support and strength (stronger than plasma membrane)
• prevents cell from bursting when water enters the cell

Question 25

chloroplasts

Answer 25

- convert carbohydrate into ATP - plants make their carbohydrate in chloroplasts from photosynthesis - have a double membrane and their own DNA - number of chloroplasts per cell can vary from just one to several hundred

Question 26

What are microtubules and what do they do?

Answer 26

- act as tracks for motor proteins - Hollow tubes made of tubulin that maintain cell shape

Question 27

What are actin filaments (microfilaments) and what is their function?

Answer 27

- enable movement (like pseudopodia) - Thin filaments made of actin that support cell shape

Question 28

What are intermediate filaments and what is their role?

Answer 28

- structural stability - Rope-like fibres made of proteins like keratin or lamins that provide mechanical strength