Molecular anatomy of genes and genomes

Question 1

How do we know life has only evolved once?

Answer 1

Because the genetic code is universal

Question 2

What is the key difference between prokaryotic and eukaryotic genomes?

Answer 2

Eukaryotic genomes are larger because they are multicellular organisms

Question 3

Draw a eukaryotic gene

Answer 3

ADD

Question 4

What does a cell function depend on?

Answer 4

What genes are expressed

Question 5

What is the purpose of the control region?

Answer 5

Determines if a gene is on or off in a particular tissue and its level of expression

Question 6

What are transcription factors?

Answer 6

Proteins that bind to the promoter sequence and control the rate of transcription

Question 7

What is a promoter?

Answer 7

The DNA sequence at which transcription factors bind and recruit RNA polymerace

Question 8

What do promoters determine?

Answer 8

If and how much a gene is transcribed

Question 9

What is splicing?

Answer 9

pre-mRNA -> mRNA

Question 10

What carries out splicing?

Answer 10

A protein complex called the spliceosome

Question 11

What is alternative splicing?

Answer 11

One gene can be spliced in different ways meaning that multiple proteins can be made

Question 12

What is the role of the 5’ cap?

Answer 12

Allows ribosomes to recognise the start of the transcript

Question 13

What is the role of the PolyA tail?

Answer 13

Stabilises transcript

Question 14

Draw a mRNA strand

Answer 14

ADD

Question 15

What % of our genome codes for proteins?

Answer 15

1.2%

Question 16

What is 48% of our genome?

Answer 16

Repetitive DNA elements

Question 17

What are the two types of repetitive DNA?

Answer 17

Highly repetitive sequences and transposons

Question 18

What are highly repetitive sequences?

Answer 18

Short regions of highly repetitive DNA which arise by replication slippage

Question 19

How can highly repetitive sequences be used for DNA fingerprinting?

Answer 19

The difference in how many of the repeats is present in the region varies greatly between individuals

Question 20

Highly repetitive sequences make up ? of the genome

Answer 20

3%

Question 21

Where do we see repetitive DNA in the cell?

Answer 21

The centromere typically consists of large arrays of repetitive DNA. Repeat sequences are added by telomerase to protect the ends of chromosomes.

Question 22

What are transposons responsible for?

Answer 22

The presence of many copies of sequences derived form transposons are responsible for much of the variation in genome sizes

Question 23

Transposons make up ? of the genome

Answer 23

45%

Question 24

? of the genome is transcribed and most of this ? encode proteins. This is called ?

Answer 24

60%
doesn’t
non-coding RNA

Question 25

What is the role of non-coding RNA?

Answer 25

Still fairly unknown however it has a regulatory role as it has the ability to feedback to the DNA and turn genes on and off

Question 26

Why do we have chromosomes?

Answer 26

Cells have a lot of DNA that has to be fitted into a very small volume but the cell needs access to it and chromosomes allow this

Question 27

What are chromosomes?

Answer 27

DNA + associated proteins

Question 28

What do chromosomes do?

Answer 28

- compacts DNA - protects DNA - Ensures replicated DNA its properly segregated - Provides an organisation to DNA

Question 29

DNA + histone proteins = ?

Answer 29

Nucleosome

Question 30

How is a nucleosome formed?

Answer 30

DNA is wrapped around positively charged histone proteins forming a nucleosome.

Question 31

What happens after a nucleosome is formed?

Answer 31

Histone H1 induces tighter DNA wrapping around the nucleosome compacting the DNA. This is then further compacted into a 30nm chromatin fiber

Question 32

What happens after a chromatin finer is formed?

Answer 32

Loops of DNA are attached to a protein scaffold which forms the metaphase chromosome

Question 33

What does the scaffold contain?

Answer 33

topoisomerase || and specific proteins eg condensin

Question 34

What is the DNA paradox?

Answer 34

Two opposite functions must occur simultaneously. DNA must be in stable compact structures that protects it from damage while the cell needs access to the information in the DNA

Question 35

How are histone tails modified?

Answer 35

They are chemically modified by enzymes

Question 36

How is the DNA paradox solved?

Answer 36

Modification of the histone tails allows switching between euchromatin and heterochromatin

Question 37

Euchromatin

Answer 37

DNA coding genes that are actively transcribed are more loosely packaged and are found associated with RNA plymerases

Question 38

Heterochromatin

Answer 38

DNA coding inactive genes are found associated with structural proteins and are more tightly packaged