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OCR A-level Biology > Cellular Control > Flashcards

Flashcards in Cellular Control Deck (27)
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1

What is a mutation?

A random change in the genetic material

2

Give examples of things that are mutagenic

Tobacco smoke
Ionising radiation e.g UV-light, X-rays, Gamma rays

3

In what type of cell division would an inheritable mutation occur in?

Meiosis

Affects gametes which then determines genetic makeup of the child

4

What are the two main types of mutation?

Point mutation - 1 gene is substituted for another

Insertion or deletion mutation - 1 or more nucleotides are inserted or deleted from a length of DNA

5

What are the 3 types of point mutation?

Silent
Missense
Nonsense

6

What is a silent mutation?

Nearly all amino acids have more than one triplet that codes for them

A silent mutation occurs when there is point mutation but the new triplet sequence still codes for the same amino acid

As such the protein is the same and the mutation is unnoticeable

7

What is a missense mutation?

When the change in triplet sequence causes a change in the amino acid sequence and thus a change in the primary, secondary and tertiary structures of the protein

This changes the 3D shape of the protein and can make it less effective at carrying out its function

8

Give an example of a condition that is caused by a missense mutation

Sickle cell anemia

Caused by a change in the gene for the B-Polypeptide haemoglobin

9

What is a nonsense mutation?

Where the change in the triple sequence causes it to become a stop codon

This then means the protein structure is incomplete and it will not carry out its function

10

Give an example of a condition caused by a nonsense mutation

Muscular Dystrophy

11

What is a frameshift?

Caused in insertion or deletion mutations

When a nucleotide is inserted or deleted in the sequence it causes all the other bases to move along

Because bases are read in groups of 3 this then changes all of the triplets that are down the chain from the mutation

12

What affect does a frame shift have on the polypeptide chain?

Because a frameshift affect all of the triplets after the mutation the amino acid sequence is greatly disrupted

This has a huge impact on the primary and subsequent tertiary structures and so the protein is unable to carry out its function

13

What is an expanding nucleotide triple repeat?

Some genes contain a repeating triplet such as -CAG CAG CAG-

The number of CAG triplets will increase due to meiosis from generation to generation

Once this goes past a critical number one might develop a genetic disorder

14

What is the lac Operon?

The gene sequence which codes for genes to metabolise lactose in the absence of glucose in bacteria

15

Describe how the lac operon works

In the presence of glucose, a repressor protein (produced by regulatory gene) is bound to the operator region

When lactose is present but glucose isn't lactose binds to the repressor and releases it from the operator. Lactose is the inducer

This then allows RNA polymerase to bind to the promotor region and create the enzymes needed to metabolise Lactose

Lactose is metabolised

16

What is a transcription factor?

Proteins that act within a cells nucleus by binding to different promotor regions to express different genes in different cell types

They are needed because all cells in your body have the same genome, but different cells need to express it differently

17

What are introns and exons?

Introns are non-coding regions of DNA

Exons are the areas that code for something and are expressed

18

What is the name of the process where the introns are removed from the RNA strand?

Splicing

19

What is post-translational gene regulation?

Gene regulation that happens after transcription

Often involved the activation of proteins through phosphorylation

e.g the formation of cAMP from ATP

They often form transcription factors which then affect gene expression

20

What are homeobox gene sequences and what do the control?

Genes that control the anatomical layout of an organism and ensure that all the right body parts from in the right place

21

How did scientists realise that homeobox genes were important to development of organisms?

They compared the homeobox sequences in fruit flies and mice and they were very similar

22

What is the difference between How genes and Homeobox genes?

How genes are a type of Homeobox gene that is only found in animals

23

What do hox genes actually code for?

proteins that act in the nucleus as transcription factors

they can stimulate or inhibit: mitosis, apoptosis, cell migration and regulate the cell cycle

24

What is Hayflicks constant?

The number of times a cell can divide by mitosis before dying (about 50 times)

25

What is apoptosis?

Programmed cell death (cell suicide)

26

Describe the sequence of events in apoptosis

Enzymes break down cell cytoskeleton

Cytoplasm becomes dense with organelles

Surface membrane changes and blebs form

Chromatin condenses and nuclear envelope and DNA break down

Cell breaks into vesicles which are ingested by phagocytotic cells

27

Give an example of apoptosis in development of a human?

During limb development apoptosis causes the digits to separate from each other

Preventing tumors from forming